Pilot Study November 2020

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Final Pilot Study Report

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Final Pilot Study Report

Contents List of Figures ...... v List of Tables ...... xi List of Abbreviations ...... xiv Acknowledgements ...... Error! Bookmark not defined. Executive Summary ...... xix 1.0 Introduction ...... 1-1 1.1 Background ...... 1-1 1.2 Pilot Plant Study Objectives ...... 1-2 1.3 Test Conditions Summary ...... 1-2 1.4 Water Treatment Goals ...... 1-5 2.0 Pilot Plant Configuration ...... 2-1 2.1 Flocculation and Sedimentation ...... 2-3 2.2 Ozonation Pilot Module ...... 2-4 2.3 Filtration Pilot Module ...... 2-5 2.3.1 Filter Media Configurations ...... 2-6 2.3.2 Filter Media Backwash Setpoints ...... 2-10 2.4 Solids Handling ...... 2-12 2.5 Varying Operational Parameters ...... 2-13 2.6 Water Quality Data Collection ...... 2-14 2.6.1 Comprehensive Water Quality Testing (or Measurement) ...... 2-14 2.6.2 Sampling Locations ...... 2-16 2.6.3 Online Instrumentation and Zeta Potential ...... 2-16 2.7 Discharge Compliance and Mitigation of Risk to Aquatic Life ...... 2-18 3.0 Raw Water Quality Characteristics ...... 3-1 3.1 Monthly and Seasonal Overview ...... 3-1 3.2 Temperature, Alkalinity, and pH ...... 3-4 3.3 Raw Water Turbidity ...... 3-6 3.4 Particle Counts ...... 3-7 3.5 Algae ...... 3-11 3.6 Organics ...... 3-13 3.7 Metals and Inorganics ...... 3-14 3.8 Summary ...... 3-15 4.0 Approach to Data Analysis and Quality Control ...... 4-1 4.1 Data Quality Control ...... 4-1 4.1.1 Training ...... 4-1 4.1.2 Documentation ...... 4-1 4.1.3 Online Instrumentation ...... 4-1

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4.1.4 Water Quality Bench Instruments ...... 4-2 4.1.5 Portland Water Bureau Lab Analysis ...... 4-3 4.1.6 Eurofins Contract Lab Analysis ...... 4-3 4.2 Data Analytics ...... 4-4 4.2.1 Filter Run Time and UFRVs ...... 4-4 4.2.2 Turbidity ...... 4-7 4.2.3 Head loss ...... 4-8 4.2.4 Particle Counts ...... 4-8 4.2.5 Organics Removal ...... 4-10 4.3 Data Presentation ...... 4-10 5.0 Coagulation, Flocculation, and Sedimentation ...... 5-1 5.1 Coagulation Testing and Selection ...... 5-1 5.1.1 Bench-scale Jar Testing ...... 5-1 5.1.2 Pilot Coagulation Selection–Summer/Fall ...... 5-3 5.2 Coagulation ...... 5-27 5.2.1 Summary of Pilot Coagulant Comparison ...... 5-27 5.2.2 Evaluating Effectiveness–Zeta Potential and SCM ...... 5-28 5.3 Flocculation ...... 5-30 5.4 Coagulant Aid ...... 5-31 5.5 Sedimentation ...... 5-35 5.6 Direct Filtration Testing ...... 5-37 5.7 Turbidity Spiking Study ...... 5-44 5.7.1 Influent Water Quality ...... 5-44 5.7.2 Coagulation, Flocculation, and Sedimentation ...... 5-48 5.7.3 Settled Water Quality ...... 5-49 5.8 Solids Handling Considerations ...... 5-52 5.9 Coagulation, Flocculation, and Sedimentation Summary ...... 5-55 6.0 Oxidation ...... 6-1 6.1 Ozone Kinetics ...... 6-1 6.1.1 Bench-scale Testing ...... 6-1 6.1.2 Pilot-scale Ozone Demand and Decay ...... 6-2 6.2 Chlorine Kinetics ...... 6-9 6.2.1 Pilot-scale Chlorine Demand and Decay ...... 6-9 6.3 Pre-ozonation and No Pre-oxidation ...... 6-10 6.3.1 Settled Water Quality ...... 6-10 6.3.2 Filtration Performance ...... 6-12 6.3.3 Chlorine Demand and Decay and Disinfection By-Products ...... 6-19 6.3.4 Summary ...... 6-21 6.4 Pre-chlorination and No Pre-oxidation ...... 6-22 6.4.1 Settled Water Quality ...... 6-23 6.4.2 Filtration Performance ...... 6-24 6.4.3 Summary ...... 6-26

Portland Water Bureau ii Brown and Caldwell Final Pilot Study Report

6.5 Pre-chlorination and Pre-ozonation ...... 6-26 6.5.1 Settled Water Quality ...... 6-27 6.5.2 Filtration Performance ...... 6-28 6.5.3 Chlorine Demand and Decay and Disinfection By-Products ...... 6-33 6.5.4 Summary ...... 6-35 6.6 Pre-Ozonation and Intermediate Ozonation ...... 6-35 6.6.1 Settled Water Quality ...... 6-37 6.6.2 Clean Bed Head Loss ...... 6-38 6.6.3 Impact of Ozone Contact Time Variation ...... 6-39 6.6.4 Turbidity Spiking Study ...... 6-40 6.6.5 Filtration Performance ...... 6-44 6.6.6 Chlorine Demand and Decay and Disinfection By-Products ...... 6-49 6.6.7 Summary ...... 6-52 6.7 Oxidation Testing Summary ...... 6-54 7.0 Filtration...... 7-1 7.1 Filter Aid ...... 7-1 7.2 Filter Media Type Comparison ...... 7-3 7.2.1 Clean Bed Head Loss ...... 7-4 7.2.2 Turbidity ...... 7-7 7.2.3 Particle Counts ...... 7-8 7.2.4 UFRVs ...... 7-10 7.2.5 Filter Efficiency ...... 7-11 7.2.6 Organics Removal ...... 7-12 7.2.7 Metals and Inorganics ...... 7-13 7.2.8 Biological Monitoring ...... 7-16 7.2.9 Chlorine Demand and Decay and Disinfection By-Products, and Flavor Profile Analysis ...... 7-26 7.2.10 Summary ...... 7-28 7.3 Filtration Rate Comparison ...... 7-29 7.3.1 Clean Bed Head Loss ...... 7-29 7.3.2 Turbidity ...... 7-30 7.3.3 Particle Counts ...... 7-31 7.3.4 Filter Run Times and UFRVs ...... 7-34 7.3.5 Head Loss Threshold Comparison ...... 7-35 7.3.6 Filter Efficiency ...... 7-37 7.3.7 Organics Removal ...... 7-38 7.3.8 Metals and Inorganics ...... 7-39 7.3.9 Filtration Rate Comparison Trial ...... 7-41 7.3.10 Turbidity Spiking Filtration Performance ...... 7-52 7.3.11 Biological Monitoring ...... 7-56 7.3.12 Chlorine Demand and Decay and Disinfection By-Products ...... 7-64

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7.4 Filtration Summary ...... 7-65 8.0 Summary of Pilot Plant Study Results and Findings ...... 8-1 8.1 Coagulation, Flocculation, and Sedimentation ...... 8-2 8.2 Oxidation ...... 8-3 8.3 Filtration ...... 8-4 8.4 Chlorine Demand and Decay, Disinfection By-Products, and Flavor Profile Analysis ...... 8-5 8.5 Design Considerations ...... 8-6 8.6 Regulatory Considerations for OHA ...... 8-7 9.0 References ...... 9-1 Conversion Factors for Coagulant Dosages ...... A-1 Simulated Distribution System and Disinfection Evaluation ...... B-1 Streaming Current Monitor and Zeta Potential Technical Memorandum ...... C-1 Jar Testing Reports ...... D-1 Bench-Scale Ozone Demand-Decay Testing Report ...... E-1 Filtration Rate Comparison for Additional Filter Media Designs ...... F-1 Clean Bed Head Loss Technical Memorandum ...... G-1 Turbidity Spiking Technical Memorandum ...... H-1

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List of Figures Figure ES-1. Summary of treatment trains evaluated from June 2019-June 2020 ...... xxii

Figure 1-1. Summary of pilot testing from July 2019 through June 2020 ...... 1-3

Figure 2-1. PWB pilot plant dual train process flow diagram...... 2-2 Figure 2-2. Intuitech flocculation-sedimentation module 1000 (model S300) at the pilot plant ...... 2-3 Figure 2-3. Intuitech ozonation module (model Z300) at the pilot plant ...... 2-4 Figure 2-4. Intuitech 6-column filtration module, model F300 at the pilot plant ...... 2-5 Figure 2-5. Schematic of filter media configuration, July 2019-February 2020 ...... 2-7 Figure 2-6. Schematic of filter media configuration, February-June 2020 ...... 2-9 Figure 2-7. Rain For Rent settling basin tank at the pilot plant ...... 2-12

Figure 3-1. Raw water temperature ...... 3-5 Figure 3-2. Raw water alkalinity ...... 3-5 Figure 3-3. Raw water pH ...... 3-5 Figure 3-4. Raw water turbidity on Train 2, July 2019–June 2020 ...... 3-6 Figure 3-5. Particle counts on Floc/Sed 1000 inlet ...... 3-8 Figure 3-6. Influent particle count distribution for raw water (left axis) and algal density at the intake (right axis)...... 3-10 Figure 3-7. Total algal density in the raw water intake ...... 3-11 Figure 3-8. Algal density for the five genera with the maximum densities sampled ...... 3-12 Figure 3-9. Raw water TOC levels ...... 3-13 Figure 3-10. Raw water DOC levels ...... 3-13

Figure 3-11. Raw water filtered UV254 levels ...... 3-14 Figure 3-12. Raw water iron concentrations ...... 3-15 Figure 3-13. Raw water manganese concentrations ...... 3-15 Figure 3-14. Raw water aluminum concentrations ...... 3-15

Figure 4-1. Example of data used to calculate filter run time ...... 4-6

Figure 5-1. Comparison of Filter 6 turbidity and head loss data (top) to Filter 6 turbidity and head loss data corresponding to calculated filter run times (bottom) during initial alum screening ...... 5-5 Figure 5-2. Calculated UFRVs during the initial screening of alum on Train 1, July 1–8, 2019 ...... 5-5 Figure 5-3. Filter effluent turbidities recorded during accepted filter runs during the initial screening of alum on Train 1, July 1–8, 2019 ...... 5-6 Figure 5-4. Turbidity from Filter 3 during the initial ferric coagulant screening ...... 5-8 Figure 5-5. Turbidity and head loss data from Filter 6 during the initial PACl coagulant screening ...... 5-9 Figure 5-6. Calculated UFRVs during the initial screening of PACl on Train 1, July 9–July 15, 2019 ...... 5-10

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Figure 5-7. Filter effluent turbidities recorded during accepted filter runs during the initial screening of PACl on Train 1, July 9 -July 15, 2019 ...... 5-10 Figure 5-8. Turbidity and head loss data from Filter 3 during the initial ACH coagulant screening, July 1–8, 2019 ...... 5-12 Figure 5-9. Calculated UFRVs during the initial screening of ACH on Train 2, July 1–8, 2019 ...... 5-12 Figure 5-10. Filter effluent turbidities recorded during accepted filter runs during the initial screening of ACH on Train 2, July 1–8, 2019 ...... 5-13 Figure 5-11. Calculated UFRVs during the side-by-side testing of alum and PACl at 6 and 8 gpm/sf, July 15–26, 2019 ...... 5-16 Figure 5-12. Filter effluent turbidities recorded during accepted filter runs during the side-by-side testing of alum and PACl at 6 and 8 gpm/sf, July 15–26, 2019 ...... 5-16 Figure 5-13. Calculated UFRVs during the side-by-side testing of alum and PACl at filtration rates of 8 and 12 gpm/sf, July 26-30, 2019 ...... 5-17 Figure 5-14. Filter effluent turbidities recorded during accepted filter runs during the side-by-side testing of alum and PACl at filtration rates of 8 and 12 gpm/sf, from July 26 to 30, 2019 ...... 5-18 Figure 5-15. Calculated UFRVs during side-by-side testing of alum and PACl with no filter aid, July 30- August 5, 2019 ...... 5-19 Figure 5-16. Filter effluent turbidities recorded during accepted filter runs during the side-by-side testing of alum and PACl with no filter aid, July 30-August 5, 2019 ...... 5-19 Figure 5-17. Filter run examples for coagulant testing without filter aid addition ...... 5-20 Figure 5-18. Calculated UFRVs during side-by-side testing of alum and PACl with filter aid, August 5-12, 2019 ...... 5-22 Figure 5-19. Filter effluent turbidities recorded during accepted filter runs during the side-by-side testing of alum and PACl with filter aid, August 5-12, 2019 ...... 5-22 Figure 5-20. Calculated UFRVs during side-by-side testing of alum and PACl following ozone pre-oxidation, August 20-30, 2019 ...... 5-24 Figure 5-21. Filter effluent turbidities recorded during accepted filter runs during side-by-side testing of alum and PACl following ozone pre-oxidation, August 20-30, 2019 ...... 5-24 Figure 5-22. Comparison of zeta potential and SCM observations relative to coagulation chemical dosage .... 5-28 Figure 5-23. Correlation of zeta potential and SCM readings during April 2020 ...... 5-29 Figure 5-24. Filter run hours by filter during pre-oxidant testing (January 1–21) and after the addition of coagulant aid (January 21–February 3) ...... 5-32 Figure 5-25. Calculated UFRVs by filter during pre-oxidant testing (January 1–21) and after the addition of coagulant aid (January 21–February 3) ...... 5-33 Figure 5-26. Filter effluent turbidities recorded during accepted filter runs during pre-oxidant testing (January 1–21) and after the addition of coagulant aid (January 21–February 3) ...... 5-33 Figure 5-27. Comparison of Train 1 HMI and grab samples settled water turbidity to raw water grab samples turbidity, November 18, 2019-January 6, 2020 ...... 5-36 Figure 5-28. Comparison of Train 1 HMI and grab samples settled water turbidity, July 1, 2019-May 31, 2020 ...... 5-36 Figure 5-29. Treatment train for direct filtration treatment testing, June 16-June 30, 2020 ...... 5-37 Figure 5-30. Filter effluent turbidity for direct filtration testing with pre-ozonation and intermediate- ozonation, June 18-30, 2020 ...... 5-38

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Figure 5-31. Filter run examples for direct filtration ...... 5-39 Figure 5-32. Filter run times for direct filtration testing with pre-ozonation and intermediate-ozonation, June 11–30, 2020 ...... 5-41 Figure 5-33. UFRVs for direct filtration testing, June 11–30, 2020 ...... 5-41 Figure 5-34. UFRVs for conventional filtration (April 30 to May 12, 2020) and direct filtration (June 18–June 30, 2020) with intermediate-ozonation ...... 5-42 Figure 5-35. UFRVs for conventional filtration (April 30 to May 12, 2020) and direct filtration (June 18-June 30, 2020) with pre-ozonation ...... 5-42 Figure 5-36. Process configuration and flow rates for the spiking study ...... 5-44 Figure 5-37. Influent turbidity during Turbidity Spiking Study, PACl Testing ...... 5-46 Figure 5-38. Influent turbidity during Turbidity Spiking Study, Alum Testing ...... 5-46 Figure 5-39. Influent particle counts during Turbidity Spiking Study, PACl Testing ...... 5-47 Figure 5-40. Influent particle counts during Spike Water, Alum Testing ...... 5-47 Figure 5-41. Influent and settled water turbidities for Train 1 (intermediate ozone) during the Turbidity Spiking Study, PACl Testing ...... 5-49 Figure 5-42. Influent and settled water turbidities for Train 2 (pre-ozone) during the Turbidity Spiking Study, PACl Testing...... 5-50 Figure 5-43. Influent and settled water turbidities for Train 1 (intermediate ozone) during the Turbidity Spiking Study, Alum Testing ...... 5-50 Figure 5-44. Influent and settled water turbidities for Train 2 (pre-ozone) during the Turbidity Spiking Study, Alum Testing ...... 5-51 Figure 5-45. Relationship between measured TSS in Flocculator 3 and paired Settled Water TSS ...... 5-54

Figure 6-1. Bench-scale ozone decay curves, March 2019 ...... 6-2 Figure 6-2. Pilot-scale ozone decay curve for Trains 1 and 2 for an applied pre-ozone dose of 1 mg/L from October 2019 ...... 6-3 Figure 6-3. Boxplot of Train 2 ozone residual curve for pre-ozonation with an applied ozone dose of 1 mg/L from October 2019...... 6-4 Figure 6-4. Ozone decay curves for intermediate ozonation (T1) and pre-ozonation (T2) with longer contact times, from April 2020 ...... 6-6 Figure 6-5. Ozone decay curves for intermediate ozonation (T1) and pre-ozonation (T2) with shorter contact times, from May 2020 ...... 6-7 Figure 6-6. Ozone demand throughout pilot testing, August 2, 2019-June 30, 2020 ...... 6-8 Figure 6-7. Chlorine decay curve for Train 1 when dosing at 1 mg/L and 0.3 mg/L and operating with pre- chlorination ...... 6-9 Figure 6-8. Treatment train for pre-ozonation treatment evaluation, August 30-September 30, 2019 ...... 6-10 Figure 6-9. Comparison of raw and settled water turbidity and settled water particle counts in Train 1 (No Oxidant) and raw and settled water turbidity in Train 2 (Pre-ozonation), August 30- September 29, 2019 ...... 6-11 Figure 6-10. Filter effluent turbidities recorded during accepted filter runs during side-by-side testing of pre-oxidation and no pre-oxidation, August 30-September 29 ...... 6-12 Figure 6-11. Comparison of particle counts with (Filter 1) and without (Filter 6) pre-ozonation, August 30- September 29, 2020 ...... 6-14

Portland Water Bureau vii Brown and Caldwell Final Pilot Study Report

Figure 6-12. Particle count data for pre-ozonation and intermediate ozonation when ozone was turned off, from April 29-30, 2020 ...... 6-16 Figure 6-13. Calculated UFRVs during side-by-side testing of pre-oxidation and no pre-oxidation, August 30- September 29, 2019 ...... 6-17 Figure 6-14. Filter run time from pre-oxidation and no pre-oxidation, from August 30 to September 29, 2019 ...... 6-18 Figure 6-15. SDS test results for chlorine demand and decay with pre-ozonation and no oxidant ...... 6-20 Figure 6-16. SDS Test Results for 14-day TTHMs and HAA5s with pre-ozonation and no oxidant ...... 6-20 Figure 6-17. Treatment train for pre-chlorination and no pre-oxidation, November 18-December 4, 2019 .... 6-22 Figure 6-18. Comparison of raw and settled water and settled water particle counts in Train 1 (Pre- chlorination) and raw and settled water turbidity in Train 2 (No oxidant), from November 18 to December 4, 2019 ...... 6-23 Figure 6-19. Total Particle Counts Summary for Pre-Chlorination and No Pre-Oxidation, November 18-24 and November 29-December 4, 2019 ...... 6-25 Figure 6-20. Treatment train for pre-chlorination and pre-ozonation ...... 6-27 Figure 6-21. Comparison of raw and settled water turbidity and settled water particle counts in Train 1 (Pre-chlorination) and raw and settled water turbidity in Train 2 (Pre-ozone), December 19, 2019-January 21, 2020 ...... 6-28 Figure 6-22. Filter effluent turbidities for pre-chlorination and pre-ozonation, December 19, 2019-January 21, 2020 ...... 6-29 Figure 6-23. Filter run hours for pre-chlorination and pre-ozonation, December 19, 2019-January 21, 2020 ...... 6-31 Figure 6-24. UFRVs for pre-chlorination and pre-ozonation, December 19, 2019-January 21, 2020 ...... 6-31 Figure 6-25. SDS test results for chlorine demand and decay with pre-chlorination and pre-ozonation ...... 6-34 Figure 6-26. SDS test results for 14-day TTHMs and HAA5s with pre-chlorination and pre-ozonation ...... 6-34 Figure 6-27. Pilot treatment train for intermediate ozonation and pre-ozonation evaluation, from April 3 to May 12, 2020 ...... 6-37 Figure 6-28. Comparison of raw and settled water turbidity and settled water particle counts in Train 1 (intermediate ozonation) and raw and settled water turbidity in Train 2 (pre-ozonation), April 3-May 12, 2020 ...... 6-38 Figure 6-29. Clean bed head loss over time for filters runs, April 3-May 12, 2020 ...... 6-39 Figure 6-30. Ozone applied dose and ozone residual concentration during the spiking study when dosing PACl and coagulant aid with T1 (intermediate) and T2 (pre-ozone) ...... 6-41 Figure 6-31. Applied ozone doses and ozone residual concentrations during spiking study when dosing alum with T1 (intermediate) and T2 (pre-ozone) ...... 6-42 Figure 6-32. Ozone decay curves for intermediate oxidation (Train 1) and pre-oxidation (Train 2) from un-spiked period in June 2020 ...... 6-43 Figure 6-33. Ozone decay curves for intermediate ozonation (Train 1) and pre-oxidation (Train 2) from turbidity spiking with alum on June 11, 2020 ...... 6-44 Figure 6-34. Filter turbidity, April 3-May 12, 2020 ...... 6-44 Figure 6-35. Total particle counts from all filters during the intermediate and pre-ozonation trial, April 3- May 12, 2020...... 6-45 Figure 6-36. Filter run examples for pre-ozonation and intermediate ozonation ...... 6-46

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Figure 6-37. Filter UFRV, April-May 12, 2020 ...... 6-47 Figure 6-38. Filter Run time, April 3-May 12, 2020 ...... 6-47 Figure 6-39. SDS test results for chlorine demand and decay ...... 6-50 Figure 6-40. HAA5 results at the beginning and end of the 14-day SDS period...... 6-51 Figure 6-41. TTHM results at beginning and end of the 14-day SDS period ...... 6-51

Figure 7-1. Turbidity and particle counts for Filter 6 example run when filter aid was removed ...... 7-1 Figure 7-2. Clean bed head loss throughout the testing period for acceptable filter runs for Filters 1, 2, 4, and 6, July 26, 2019-February 3, 2020 ...... 7-5 Figure 7-3. Filter effluent turbidities recorded during three operating periods: Pre-Ozone, Pre-Chlorine, and No oxidant, August 20-December 17 ...... 7-8 Figure 7-4. Filter run example for anthracite and GAC media with pre-ozonation ...... 7-10 Figure 7-5. Comparison of calculated UFRVs by media type during three operating periods: Pre-Ozone, Pre-Chlorine, and No Oxidant, August 20-December 17 ...... 7-11 Figure 7-6. Comparison of filter efficiency by filter media type ...... 7-12 Figure 7-7. Total aluminum in anthracite filter effluent, August 20-December 17, 2019 ...... 7-14 Figure 7-8. Total aluminum in GAC filter effluent, August 20-December 17, 2019 ...... 7-14 Figure 7-9. Total iron in anthracite filter effluent, August 20–December 17, 2019 ...... 7-15 Figure 7-10. Total iron in GAC filter effluent, August 20–December 17, 2019 ...... 7-15 Figure 7-11. Total manganese in anthracite filter effluent, August 20–December 17, 2019 ...... 7-15 Figure 7-12. Total manganese in GAC filter effluent, August 20–December 17, 2019 ...... 7-16 Figure 7-13. Dry (adjusted) filter media ATP, December 2019–February 2020 prior to filter media change ..... 7-17 Figure 7-14. Forms of natural organic matter ...... 7-18 Figure 7-15. AOC concentration by sample location, August–October 2019 ...... 7-19 Figure 7-16. AOC concentration by sample location, November 2019-January 2020 ...... 7-20 Figure 7-17. Statistical summary of AOC data, July 2019-January 2020 ...... 7-21 Figure 7-18. Summary of carboxylic acid data collected on January 15, 2020 ...... 7-22 Figure 7-19. EPS measured as polysaccharides and proteins in sample FM 104 (Filter 1, anthracite) compared to sample FM 304 (Filter 3, GAC) from February 3, 2020 ...... 7-23 Figure 7-20. SEM images of samples taken from sample FM 104 (Filter 1, anthracite) ...... 7-24 Figure 7-21. SEM images of samples taken from sample FM 304 (Filter 3, GAC) ...... 7-25 Figure 7-22. PHO: GLY ratio in each filter sample ...... 7-26 Figure 7-23. Clean bed head loss over time for all filters, February 24-May 12, 2020 ...... 7-29 Figure 7-24. Filter effluent turbidities recorded, February 24-May 12, 2020 ...... 7-30 Figure 7-25. Filter run examples for loading rate testing ...... 7-31 Figure 7-26. Total particle counts from all filters, February 24-May 12, 2020 ...... 7-32 Figure 7-27. Filter run hours for accepted filter runs, February 24-May 12, 2020 ...... 7-34 Figure 7-28. Filter UFRVs for accepted filter runs, February 24-May 12, 2020 ...... 7-34 Figure 7-29. Filter run time when terminated on 10 ft of head loss compared to 12 ft of head loss for accepted filter runs, February 24-May 12, 2020 ...... 7-35

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Figure 7-30. Filter UFRVs when terminated on 10 ft of head loss compared to 12 ft of head loss for accepted filter runs, February 24–May 12, 2020 ...... 7-36 Figure 7-31. Comparison of filter efficiency by filtration rate ...... 7-37 Figure 7-32. Total aluminum in Train 1 filter effluent, February 24–May 12, 2020 ...... 7-39 Figure 7-33. Total aluminum in Train 2 filter effluent, February 24–May 12, 2020 ...... 7-39 Figure 7-34. Total iron in Train 1 filter effluent, February 24–May 12, 2020 ...... 7-40 Figure 7-35. Total iron in Train 2 filter effluent, February 24–May 12, 2020 ...... 7-40 Figure 7-36. Total manganese in Train 1 filter effluent, February 24-May 12, 2020 ...... 7-40 Figure 7-37. Total manganese in Train 2 filter effluent, February 24-May 12, 2020 ...... 7-41 Figure 7-38. Average run time with pre-ozonation, over all filtration rates testing, May 12-May 26, 2020 ..... 7-44 Figure 7-39. Average UFRVs with pre-ozonation, over all filtration rates testing, May 12-May 26, 2020 ...... 7-44 Figure 7-40. Head loss accumulation by filtration rate (6, 8, 10, and 12 gpm/sf) for each acceptable filter run, May 12-May 26, 2020 ...... 7-47 Figure 7-41. Head loss accumulation for the 60-inch media filters at all filtration rates (6, 8, 10, and 12 gpm/sf) for each acceptable filter run, May 12-May 26, 2020 ...... 7-48 Figure 7-42. Head loss accumulation for the 66-inch media filters at all filtration rates (6, 8, 10, and 12 gpm/sf) for each acceptable filter run, May 12-May 26, 2020 ...... 7-48 Figure 7-43. Head loss accumulation curves for the 72-inch media filters at all filtration rates (6, 8, 10, and 12 gpm/sf) for each acceptable filter run, May 12-May 26, 2020 ...... 7-49 Figure 7-44. Average UFRV for Train 1 (12 gpm/sf) and Train 2 (10 gpm/sf) both with pre-ozonation evaluated with the 10-ft head loss threshold compared to 12-ft threshold, May 12–18, 2020 .... 7-50 Figure 7-45. Average UFRV for Train 1 (6 gpm/sf) and Train 2 (8 gpm/sf) both with pre-ozonation evaluated with the 10-ft head loss threshold compared to 12-ft threshold from May 18–26, 2020...... 7-50 Figure 7-46. Raw, settled, and filter effluent turbidity during turbidity spiking study, alum testing ...... 7-53 Figure 7-47. Filter head loss during turbidity spiking study, alum testing ...... 7-55 Figure 7-48. Comparison of dry (adjusted) filter media ATP on the top of the filter column, March 10- May 12, 2020...... 7-57 Figure 7-49. AOC concentration by sample location from February, March, and April 2020 ...... 7-58 Figure 7-50. Summary of AOC collected on June 2, 2020 ...... 7-59 Figure 7-51. Statistical summary of AOC data, February-June 2020 ...... 7-60 Figure 7-52. Carboxylic acid concentrations measured in samples collected on March 18, 2020 ...... 7-61 Figure 7-53. Summary of carboxylic acid data collected on April 7, 2020 ...... 7-61 Figure 7-54. Summary of carboxylic acid data collected on May 5, 2020 ...... 7-62 Figure 7-55. Summary of carboxylic acid data collected on May 26, 2020, with Train 1 operating at 6 gpm/sf and Train 2 operating at 8 gpm/sf ...... 7-63 Figure 7-56. Summary of carboxylic acids collected on June 2, 2020 ...... 7-63

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List of Tables Table ES-1. Pilot Study Water Quality Goals and Performance Benchmarks ...... xxi Table ES-2. Filter Media Designs Operated from July 2019–February 2020 ...... xxvi Table ES-3. Filter Media Comparison Summary ...... xxvii Table ES-4. Filter Media Designs Operated from February 2020–June 2020 ...... xxviii Table ES-5. Filter Media Designs for OHA Approval ...... xxxi

Table 1-1. Pilot Study Water Quality Goals and Performance Benchmarks ...... 1-7

Table 2-1. Six-Filter Configuration ...... 2-6 Table 2-2. Filter Media Profile Sieve Results (Specification), July 2019–February 2020 ...... 2-8 Table 2-3. Sieve Results (Specifications) for Filter Media Profiles Operated from February–July 2020 ...... 2-10 Table 2-4. Backwash Initiation Criteria and Operation for GAC and Anthracite Media Configuration, July 1, 2019–February 3, 2020 ...... 2-11 Table 2-5. Adjusted High-Rate Backwash Rate for Anthracite-Only Media Configuration, February 18– June 30, 2020 ...... 2-11 Table 2-6. Unit Process Variables, July 2019-June 2020, Excluding Turbidity Spiking Study ...... 2-13 Table 2-7. Conversion Factors for Aluminum–Based Coagulant Dosages ...... 2-14 Table 2-8. Comprehensive Water Quality Parameters and Frequency ...... 2-15

Table 3-1. Average (Minimum–Maximum) Monthly Pilot Raw Water Quality, July 2019–June 2020 ...... 3-2 Table 3-2. Average Seasonal Pilot Raw Water Quality, July 2019–June 2020 ...... 3-3

Table 5-1. Raw Water Quality Summary for Bench-scale Jar Testing ...... 5-2 Table 5-2. Average Organics Reduction During the Initial Screening of Alum on Train 1, July 1-8, 2019 ...... 5-7 Table 5-3. TOC Removal During the Initial Ferric Coagulant Screening, July 9–15, 2019 ...... 5-8 Table 5-4. Average Organics Reduction During the Initial Screening of PACl on Train 1, July 9–15, 2019 ...... 5-11 Table 5-5. Average Organics Reduction During the Initial ACH coagulant Screening, July 1–8, 2019 ...... 5-14 Table 5-6. Summary of Chemical Dosing Scenarios for Alum and PACl Comparison ...... 5-15 Table 5-7. Particle Counts Summary for Alum and PACl with no Filter Aid, July 31-August 5, 2019 ...... 5-21 Table 5-8. Particle Counts Summary from Side-by-Side Testing of Alum and PACl, August 5-12, 2019 ...... 5-23 Table 5-9. Pre-ozonated Water and Filter Effluent Particle Counts Summary from Side-by-Side Testing of Alum and PACl, August 20–30, 2019 ...... 5-25 Table 5-10. Average TOC Removal During Alum and PACl Side-by-Side Comparison, July 16– August 30, 2019 ...... 5-26

Table 5-11. Average Reduction of UV254 During Alum and PACl Side-by-Side Comparison, July 15– August 30, 2019 ...... 5-26 Table 5-12. Flocculation Detention Times Dependent on Operational Configuration ...... 5-31 Table 5-13. Flocculation Mixing Velocity Changes, June 2019-June 2020 ...... 5-31

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Table 5-14. Raw and Ozonated Water and Filter Effluent Particle Counts During Pre-Oxidant Testing Before (January 1 to 21) and After the Addition of Coagulant aid (January 21 to February 3) ...... 5-34 Table 5-15. Particle Counts Summary from Direct Filtration Testing, June 18–30, 2020 ...... 5-40 Table 5-16. Average TOC Removal During Direct Filtration Operation, June 18-30, 2020 ...... 5-43 Table 5-17. Average UV254 Reduction During Direct Filtration Operation, June 18-30, 2020 ...... 5-43 Table 5-18. Average Grab Sample Results of Pilot Influent Water Quality Parameters During Turbidity Spiking Study ...... 5-45 Table 5-19. Average Online Monitoring Results of Pilot Influent During Turbidity Spiking Study ...... 5-45 Table 5-20. Train 1 (intermediate ozonation) TSS results ...... 5-51 Table 5-21. Train 2 (pre-ozonation) TSS results ...... 5-51

Table 6-1. Minimum Ozone Concentrations Detectable by Ozone Residual Analyzers ...... 6-3 Table 6-2. Pilot-scale Ozone Decay Kinetics for Treatment of Raw Watera ...... 6-5 Table 6-3. Particle Counts Summary of Pre-ozonation and No Pre-oxidation, August 30-September 29 ..... 6-13 Table 6-4. Average TOC Removal During Pre-Ozonation and No Pre-Oxidation Testing, August 30-September 29, 2020 ...... 6-18 Table 6-5. Average Filtered UV254 Reduction During Pre-Ozonation and No Pre-Oxidation Testing, August 30-September 29, 2020 ...... 6-19 Table 6-6. Summary of Filter Performance for Pre-Chlorination and No Pre-Oxidation ...... 6-24 Table 6-7. Average Organics Removal During Pre-Chlorination and No Pre-Oxidation Testing, November 18-24, and November 29-December 4, 2019 ...... 6-26 Table 6-8. Particle Counts Summary of Pre-Chlorination and Pre-Ozonation, December 19, 2019- January 21, 2020 ...... 6-30 Table 6-9. Average TOC Removal Through Filtration, December 19, 2019-January 21, 2020...... 6-32 Table 6-10. Average Filtered UV254 Reduction Through Filtration, December 19, 2019-January 21, 2020 ...... 6-32 Table 6-11. Summary of Testing Scenarios for Pilot Plant Study, April 3-May 12, 2020 ...... 6-36 Table 6-12. Estimated Ozone Demands ...... 6-41 Table 6-13. Average TOC Removal Through Filtration, April 3–May 12, 2020 ...... 6-48 Table 6-14. Average Filtered UV254 Reduction Through Filtration, April 3-May 12, 2020 ...... 6-48

Table 7-1. Average (Minimuma–Maximum) Filter Aid Doses per Season for Train 1 and Train 2 ...... 7-2 Table 7-2. Test Duration and Pretreatment Conditions for Filter Media Type Comparison ...... 7-4 Table 7-3. Clean Bed Head Loss for All Filters, January 30-February 3, 2020 ...... 7-6 Table 7-4. Observed Decrease in CBHL Following Chlorine Soak ...... 7-7 Table 7-5. Particle Counts Summary, Averaged by Media Type, August 20-December 17, 2019 ...... 7-9 Table 7-6. Average TOC Removal by Media Type and Pretreatment Condition, August 20- December 17, 2019 ...... 7-13 Table 7-7. Average Reduction of UV254 by Media Type and Pretreatment Condition, August 20- December 17, 2019 ...... 7-13 Table 7-8. Tabulated EPS Proteins and Polysaccharides ...... 7-24 Table 7-9. Comparison by Media of CDD, October and November 2019 SDS Testing ...... 7-27 Table 7-10. Comparison by Media of 14-day DBP Formation, October and November 2019 SDS Testing ...... 7-27

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Table 7-11. Filter Media Comparison Summary ...... 7-28 Table 7-12. Raw Water and Filter Effluent Particle Counts Summary, April 3–May 12, 2020 ...... 7-33 Table 7-13. UFRV Averages for 10- and 12-ft Head Loss Threshold ...... 7-36 Table 7-14. Average TOC Removal by Filter, February 24-May 12, 2020 ...... 7-38 Table 7-15. Average UV254 Reduction by Filter, February 24-May 12, 2020 ...... 7-38 Table 7-16. Turbidity for each Filter Design with Pre-Ozonation, over all Filtration Rates Tested, May 12-May 26, 2020 ...... 7-42 Table 7-17. Ozonated Water and Filter Effluent Particle Counts Summary, May 12-May 18, 2020 ...... 7-42 Table 7-18. Ozonated Water and Filter Effluent Particle Counts Summary, May 18-May 27, 2020 ...... 7-43 Table 7-19. Filter Runs Removed from Analysis Due to Early Manual Termination ...... 7-45 Table 7-20. Average UFRV Train 1 (12 gpm/sf) and Train 2 (10 gpm/sf) Both with Pre-Ozonation Evaluated for 10- and 12-ft Head Loss Threshold, May 12-May 18, 2020...... 7-51 Table 7-21. Average UFRV for Train 1 (6 gpm/sf) and Train 2 (8 gpm/sf) Both with Pre-Ozonation Evaluated With the 10-ft Head Loss Threshold Compared to 12-ft Threshold, May 18-May 26, 2020 ...... 7-51 Table 7-22. Average TOC Removal by Filter Design During the Filtration Rate Trial ...... 7-52 Table 7-23. Summary of Raw Water and Filter Effluent Turbidity and Particle Counts During the Turbidity Spiking Study, Alum Testing ...... 7-54 Table 7-24. Filter Runs' UFRVs and Estimated UFRVs During the Turbidity Spiking Test, June 10–11, 2020 .... 7-56 Table 7-25. Summary of Empty Bed Contact Times ...... 7-57 Table 7-26. SDS Test Results for CDD from April 22, 2020, by Filtration Rate ...... 7-64 Table 7-27. DBP Results from April 22, 2020, by Filtration Rate ...... 7-64

Table 8-1. Estimated Ozone Demands ...... 8-4 Table 8-2. Filter Media Designs for OHA Approval ...... 8-8

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List of Abbreviations °C degree centigrade HAA5 sum of 5 haloacetic acids ACH aluminum chlorohydrate HPLC high performance liquid Alum hydrated aluminum sulfate chromatography am amorphous HMI human machine interface AOC assimilable organic carbon HRT hydraulic residency time ICP-MS inductively coupled plasma mass ATP adenosine triphosphate spectrometry AWOP OHA’s Area-Wide Optimization Program in. inch IQR interquartile range BC Brown and Caldwell k decay constant CaCO3 calcium carbonate CBHL clean bed head loss L/d length to diameter ratio CDD chlorine demand and decay L/mg-m Liters per milligram, meter CFE combined filter effluent LRAA locational running annual average MCL maximum contaminant level cm centimeter µg/L micrograms per liter CU University of Colorado DBPs disinfection by-products µm micrometer or micron DO dissolved oxygen MDL minimum detection limit DOC dissolved organic carbon mgd million gallons per day mg/L milligrams per liter DPD N,N Diethyl-1, 4 Phenylenediamine Sulfate min minute EBCT empty bed contact time mm millimeter ECD electron capture detection MRL method reporting limit EPA U.S. Environmental Protection Agency MS mass spectrometry FE filter effluent MUL maximum use limit Ferric ferric chloride ng/L nanogram per liter FI filterability index nm nanometer Filtration Facility Bull Run Filtration Facility NOM natural organic matter Floc/Sed 1000 Flocculation Sedimentation 1000 NDMA N-nitrosodimethylamine ft foot/feet NPDES National Pollutant Discharge Elimination System FTW filter-to-waste NSF NSF International GAC granular activated carbon NTU nephelometric turbidity unit g/mol grams per mole gal/sf gallons per square foot OHA Oregon Health Authority GC gas chromatography PACl polyaluminum chloride gpd gallons per day particles/mL particles per milliliter PES polyethersulfone gpm gallons per minute

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pg picogram PID proportional integral derivative PSW Partnership for Safe Water Pt-Co Platinum-Cobalt units PWB Portland Water Bureau Report Final Pilot Study Report scfm standard cubic feet per minute SCM streaming current monitor SCU streaming current unit SDS simulated distribution system sf square foot SLR surface loading rate SM Standard Method SOP standard operating procedure SOR surface overflow rate SUVA specific UV absorbance T&O taste and odor TAC Technical Advisory Committee TOC total organic carbon TSS total suspended solids TTHMs total trihalomethanes UCMR2 Unregulated Contaminant Monitoring Rule UFRV unit filter run volume, gallon/sf-run UV ultraviolet UVA ultraviolet absorbance

UV254 ultraviolet absorbance at 254 nanometers, m-1 Work Plan 2019 Pilot Plant Work Plan ZLD Zero liquid discharge

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Acknowledgements

Preparation of this Final Pilot Study Report was a collaboration between Portland Water Bureau and Brown and Caldwell. Lead Authors are shown in blue and bold font. Particular individuals are recognized for their contribution to this report and the Portland Water Bureau Pilot Program as follows:

Portland Water Bureau (Core Pilot Team) Portland Water Bureau Pilot Operations Team Yone Akagi, P.E. (Monthly Rotation) Kimberly Gupta, P.E. Kevin Ceniceros, T4 D4 Mac Gifford, Ph.D., P.E., Pilot Operations Lead Steve Mauter, D2 T3 Anna Vosa, P.E. Rick Norris, D2 T4 Lyda Hakes, P.E. James Carter, T3 Mojtaba Azadiaghdam, Ph.D. Simon Kalpin, T2 Thomas Krause, D2 Tim Anderson, D2 T1 Humberto Piedra-Ruiz John White, T2 Melanie Roy Warampa (Gam) Thiramoke, T3

Brown and Caldwell Lynn Stephens, P.E., Pilot Study Manager Joanie Stultz, P.E. Damon Roth, P.E., BCEE Karina Eyre Mia Vijanderan Bill Persich, P.E.

In addition, the report was developed with support from the Pilot Technical Advisory Committee (TAC) members, Filtration Facility Design Team (Stantec/Carollo), and others who contributed to the appendices. Pilot Technical Advisory Committee Stantec/Carollo Issam Najm, Ph.D., P.E., BCEE, WQTS, Inc. Patrick Carlson, P.E. Mark LeChevallier, Ph.D., Dr. Water Consulting

Appendix A: Conversion Factors for Coagulant Dosages Damon Roth, Brown and Caldwell Appendix B: Simulated Distribution System and Disinfection Evaluation Anna Vosa, Portland Water Bureau Appendix C: Streaming Current Monitor and Zeta Potential Technical Memorandum Mojtaba Azadiaghdam, Portland Water Bureau Appendix D: Jar Testing Reports Alex Mofidi, Confluence Engineering Appendix E: Bench-Scale Ozone Demand-Decay Testing Report Steve Shiokari, Brown and Caldwell Dr. Scott Summers’ Research Group, University of Colorado-Boulder Appendix F: Filtration Rate Comparison for Additional Filter Media Designs Damon Roth, Brown and Caldwell Appendix G: Clean Bed Head Loss Technical Memorandum Mac Gifford, Portland Water Bureau Appendix H: Turbidity Spiking Technical Memorandum Mac Gifford and Core Pilot Team, Portland Water Bureau

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Executive Summary

This Final Pilot Study Report (Report) describes the pilot testing that was conducted on the Portland Water Bureau’s (PWB’s) Bull Run Supply. The pilot testing was completed to assist PWB in transitioning to a new greenfield water filtration facility, referred to as the Bull Run Filtration Facility (Filtration Facility). The Filtration Facility is scheduled to be in service in 2027. This Report covers the 12-month pilot study testing period from June 2019 through June 2020.

This Report meets the requirement of providing pilot study results by November 30, 2020 per the 2017 Bilateral Compliance Agreement between the Oregon Health Authority (OHA) and PWB (OHA 2017). PWB has in place a watershed protection and monitoring program for the Bull Run Watershed, which has maintained this high-quality source water and enabled PWB to provide safe and reliable drinking water to the City of Portland and wholesale customers for generations. This watershed protection and monitoring program has been the basis for maintaining a filtration exemption and, more recently, a variance to the treatment requirements of the Long Term Enhanced Surface Water treatment Rule (LT2 Rule). However, a string of low-level Cryptosporidium oocysts detections that started in 2017 required enacting further treatment per that agreement (OHA 2017).

PWB selected granular media filtration as the means to achieve Cryptosporidium oocysts removal. The pretreatment ahead of granular media filtration, as well as the media selection and design criteria for granular media filtration itself, has been informed based on this pilot study and a larger decision-making process. The planning phase for the Filtration Facility included a full year of engineering studies, investigations, analyses, workshops, and tours of water treatment facilities and key outcomes are documented in the Project Definition Report (BC 2020). Predesign efforts overlapped with the final six months of the pilot testing covered in this Report, allowing for collaboration with the design team. Building on the Project Definition Report effort, several workshops were held with PWB staff, the Design Team, Brown and Caldwell (BC), and a Technical Advisory Committee (TAC). In these workshops, treatment process alternatives were evaluated for both their ability to effectively treat every day water quality conditions including reducing sediment loading into the distribution system and reducing disinfection by-products (DBPs) in customer taps, as well as providing future resiliency to possible future watershed events such as storms, algal blooms, wildfires, or landslides.

This pilot study focused on treatment of the high-quality Bull Run Watershed source water, which is maintained through the existing watershed protection program that serves as the first barrier in a multi-barrier approach towards risk reduction and excellent finished water quality. Overall, the pilot study has demonstrated that a variety of treatment options can be effective in meeting water quality objectives. All of the explored treatment trains will remove Cryptosporidium from the source water. Other water quality benefits have been observed, including significantly reducing the levels of DBPs. Treatment options including oxidation, such as ozone, demonstrated improvements in fine particle control in the filter effluent as well as

Portland Water Bureau xvii Brown and Caldwell Final Pilot Study Report │ Executive Summary

increases in filter efficiency and productivity. All high-rate granular filter media designs tested were shown to surpass water quality objectives, regulatory requirements, and productivity goals.

Objectives and Water Quality Goals

The main objectives of the pilot study were to: • Inform treatment process selection for the Filtration Facility, • Support development of a sound, buildable, and operable basis of design for the Filtration Facility that meets regulatory requirements, • Inform design parameters and seasonal operating parameters, • Evaluate data for consistency and potential future considerations of Partnership for Safe Water (PSW)/OHA’s Area-Wide Optimization Program (AWOP), and • Serve as an educational tool for engineers and operators, and engagement in treatment process understanding.

The pilot study developed several water treatment goals and benchmarks summarized in Table ES-1. The operational goals for turbidity were based on PSW Phase IV Performance Goals (PSW 2014) and OHA’s AWOP to target a turbidity less than 0.1 nephelometric turbidity units (NTU) for 95 percent of the operational time. Particle counts were used as a surrogate to demonstrate removals of Cryptosporidium oocysts (3- to 5-micrometer [µm] diameter) and Giardia cysts (5 to 15 µm diameter) in the filtered water. The goals for DBPs were to reduce total trihalomethanes (TTHMs) and the sum of five haloacetic acids (HAA5s) to less than half of their respective maximum contaminant levels (MCLs).

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Table ES-1. Pilot Study Water Quality Goals and Performance Benchmarks Regulatory Parameter Location Operational Goalb Comments on Operational Goal Requirementa Overview of PSW and OHA’s AWOP Program: ≤ 2.0 NTU, 95% of monthly • ≤ 1.0 NTU, 95% of the time when Settled waterc No requirement samplesd source turbidity ≤ 10 NTU, and • ≤ 2.0 NTU, 95% of the time when source water turbidity > 10 NTU. Turbidity Operational goal matches PSW Phase IV ≤ 0.3 NTU, 95% of ≤ 0.10 NTU, 95% of the Performance goal; OHA’s AWOP operational the monthly filter run time goal is below LT2 Microbial Toolbox credit Individual filter samplesf effluent (FE)e of 0.15 NTU. ≤ 1 NTU at any ≤ 0.30 NTU, 100% of the Operational goal matches PSW Phase IV timef filter run time Performance Goal; OHA’s AWOP. < 50 particles/mL at 5– Particle count goals are surrogates for Individual FEe 15 µm, 95% of the Cryptosporidium and Giardia removal. operational time or Particle counts No requirement Individual FEe 2.0-log removal from raw Particle count goals are surrogates for compared to water for 3–5 µm and 2.5- Cryptosporidium and Giardia removal; raw log removal for 5–15 µmg assumes sedimentation in operation. MCL = 80 ≤ 40 µg/L for chosen TTHM SDS micrograms per treatment scheme based MCLs based on locational running annual liter (µg/L) on DBP SDS testing average (LRAA) of samples collected in distribution system; operational goal (half ≤ 30 µg/L for chosen MCL) is also a trigger for reduced DBP HAA5 SDS MCL = 60 µg/L treatment scheme based monitoring. on DBP SDS testing Minimum Unit > 6,500 gallon/sf-run, 95% Backwash based on turbidity, head loss, and Filter Run h of the operational time run time triggers; operational goal is based Volume (UFRV) Individual filter No requirement on estimated minimum to meet water > 10,000 gal/sf-run, 95% of Desired UFRV production goals. the time Operational goal based on wanting to Filter-to-waste ≤ 5% of total UFRV, 95% of FTW No requirement achieve an filter efficiency of at least 95% (FTW) Cycle the operational time during filter operations. a. Regulatory requirement meets federal and state requirements. b. The operational goal is modeled from PSW and OHA’s AWOP and is an internal PWB goal, not based on regulatory requirements. c. Applicable when operating in conventional filtration mode. d. Optimal turbidity will be determined based on producing filterable floc. Settled water turbidities greater than 1 NTU were often required even when raw water turbidity was less than 10 NTU to achieve filtration goals. e. Individual FE samples will be analyzed continually and recorded every 5 minutes. f. Regulatory requirement is based on combined filter effluent (CFE). Pilot study monitoring based on individual FE. g. When operating in direct filtration mode, 2.0-log removal from raw water for 3 to 5 µm range and 2.0-log removal for 5 to 15 µm range. h. The minimum UFRV is based on a filter loading rate of 12 gallons per minute (gpm) per square foot (sf) and a desired plant production of 145 million gallons per day (mgd) with 8 filters and 1 filter out of service.

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Treatment Trains Evaluated

The pilot plant consisted of two treatment trains, each containing treatment modules for ozonation, flocculation/sedimentation, and filtration. Each treatment train served three filter columns, operated in parallel and loaded with anthracite or granular activated carbon (GAC) media over sand. The treatment trains were configured to evaluate the following treatment processes: • Conventional and direct filtration • Ozonation (pre-ozonation and intermediate ozonation) • Pre-chlorination • Granular media filtration

Figure ES-1 summarizes the key treatment trains evaluated from June 2019 to June 2020 to investigate filtration design, pretreatment approaches, and meet the study objectives.

Figure ES-1. Summary of treatment trains evaluated from June 2019-June 2020

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Summary of Testing Findings

All treatment trains evaluated through this pilot testing effort produced water quality that was superior to drinking water quality requirements. A few processes, including pre-chlorination pre-ozonation, intermediate ozonation and sedimentation provided added benefits. Ozonation produced excellent water quality, increased filter productivity, and further reduced DBP formation. All of the filter media designs tested performed well for their design loading rates. Filters tested at filter loading rates up to 12 gallons per minute per square foot (gpm/sf) consistently produced water with filter effluent turbidity well below 0.1 NTU, much lower than regulatory thresholds. Additional details of the findings by process are described below.

Raw Water Quality

During this pilot study, raw water was representative of historical raw water typically observed in the Bull Run watershed (BC 2020). Influent turbidity, pH, alkalinity, algae, and organics levels were within expected ranges and followed typical seasonal patterns. The raw water turbidity ranged between 0.2 and 1.3 nephelometric turbidity units (NTU) with the monthly average raw water turbidity between 0.3 and 0.5 NTU during the study period (excluding the turbidity spiking trial). Because there were no naturally occurring elevated turbidity events during the course of this study, a turbidity event was simulated to test the pilot beyond typical operating conditions. The spiking solution was created using native soil from the Bull Run Watershed that was assessed and determined to likely be indicative of the type of soil that would stay suspended in the reservoir following a storm event. The spiking solution was able to achieve a pilot influent turbidity level of approximately 20 NTU for a duration of 30 hours, including a brief spike of turbidity up to 100 NTU for approximately 40 minutes. The spiking target of approximately 20 NTU was selected to simulate a turbidity event that might follow a severe storm in the watershed, but was not intended to represent a catastrophic event.

The full-scale Filtration Facility is being designed as a zero liquid discharge (ZLD) facility, meaning that treated liquid residuals will be recycled to the Filtration Facility inlet. Although these recycle flows are limited to a fraction of the total inlet flow by the Filter Backwash Recycling Rule, they may have some impact on the inlet water quality that is treated by the full-scale Filtration Facility. The impact from these recycle streams could not be evaluated at pilot scale.

Coagulation, Flocculation, and Sedimentation

Four primary coagulants (alum, ferric chloride, polyaluminum chloride [PACl], and aluminum chlorohydrate [ACH]) were evaluated during bench- and pilot-scale testing. PACl and alum both performed well at the pilot-scale in terms of filter productivity and organics removal, and offered better performance than ferric chloride or ACH under the conditions tested. PACl was used as the primary coagulant for the majority of testing because it performed as well as alum and did not require supplemental alkalinity for successful coagulation. For all testing except the turbidity spiking study, coagulant dosages ranged from 0.04 to 2.08 mg/L as Al3+ or Fe3+ and the PACl dose ranged from 0.1 - 1.1 mg/L as Al3+. PWB will continue to evaluate coagulants with the pilot test equipment.

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Due to such low raw water turbidity, settled water turbidity was often higher than pilot influent. Settled water turbidity was a poor indicator of coagulation performance. Other indicators that were found to be more useful to monitor coagulation were filtered water quality, filter productivity, streaming current monitor (SCM) readings, and zeta potential readings. It is difficult to mimic full-scale sedimentation at pilot-scale, and performance full- scale could be better than what was experienced at the pilot-scale. The settled water turbidity was anticipated to be higher than the raw water turbidity (due to the low raw water turbidity and addition of a coagulant) and so this performance finding was as expected.

A conventional treatment process (including coagulation, flocculation, sedimentation, and filtration) provided added benefit compared to direct filtration. Even though the sedimentation process does not capture the majority of solids produced at the pilot plant under normal operations, comparison of equivalent conditions between conventional treatment and direct filtration treatment found that filtration was more productive with sedimentation than with direct filtration. Under typical raw water quality conditions, both conventional treatment and direct filtration were able to meet filtered water quality goals. Coagulant aid addition also improved filtration performance during winter conditions when using PACl.

The benefits of conventional treatment were evaluated through the turbidity spiking trial. Raw water turbidity was increased to approximately 20 NTU. Initially, PACl was used as the primary coagulant, which produced good filtered water quality at a charge-neutral dose, but the settled water turbidity was higher than preferred and a settleable floc was not produced. Given this fact, the coagulant was switched to alum during the turbidity spiking trial. Alum was supplemented with sodium bicarbonate (to supplement alkalinity) to target a pH of 7 and alkalinity around 20 milligrams per liter (mg/L) as CaCO3 in the settled water. Alum in combination with sodium bicarbonate provided lower settled water turbidity and approximately 75 percent of the raw water turbidity was removed through coagulation, flocculation, and sedimentation. Filtered water quality was excellent and is further described below.

Oxidation

Pre-oxidation was evaluated during this study for the purposes of enhancing conventional filtration and improving finished water quality; the study did not evaluate pre-oxidation for the purpose of procuring pre-filtration disinfection credit. Oxidant testing results comparing pre- ozonation, pre-chlorination, and intermediate ozonation showed that oxidation is important to meet the performance goals for the Filtration Facility. Pre-oxidation provided better filter productivity and lower filter effluent particle counts compared to no pre-oxidation, allowing the filters to maintain productivity at or above unit filter run volume (UFRV) goals. General observations comparing oxidants are summarized below.

During the fall season of ozone testing when organics are usually highest, an applied ozone dose of 1.0 mg/L resulted in an ozone residual of less than 0.1 mg/L after an ozone contact time of approximately 14 minutes. During the spring season, the ozone contact time was reduced from 13 and 16 minutes to 8 minutes in both trains. The reduction in ozone contact time to

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8 minutes did not compromise filter performance. Filter productivity and the average filter effluent TOC concentrations were comparable at both ozone contact times. Pre-ozonation and No Pre-oxidant Pre-ozonation significantly improved filter productivity. On average, the 50th percentile UFRVs with pre-ozonation were 1.5 times greater than the filters with no pre-oxidant. Pre-ozonation improved ultraviolet absorbance at 254 nanometers (UV254) reduction (an average of 92 percent reduction of UV254 in the ozonated train compared to 78 percent reduction in the train with no pre-oxidant). Good color removal (below the method reporting limit [MRL]) and total organic carbon (TOC) removal (approximately 50 percent) occurred regardless of pre- oxidation, indicating that coagulation plus filtration is achieving a high amount of organics removal. Pre-ozonation and Pre-chlorination Both pre-ozonation and pre-chlorination were effective pre-oxidation methods. The notable results from the side-by-side comparison of pre-chlorination and pre-ozonation were as follows: • Particle counts in the filter effluent from both pre-chlorination and pre-ozonation were low with the 50th percentile ranging from 1 to 2 particles per milliliter (particles/mL) for all filters. • Filter productivity was generally higher with pre-ozonation than pre-chlorination for the conditions tested. • Both pre-oxidation strategies produced low DBPs (less than one-quarter of the MCL). Compared to the sample collected from PWB’s distribution system entry point, the Lusted Hill Treatment Facility Outlet, DBPs were reduced by 60 to 90 percent. DBP concentrations were lower with pre-ozonation than pre-chlorination. Intermediate Ozonation and Pre-ozonation Overall, performance with intermediate and pre-ozonation were comparable, providing effective treatment in both ozonation modes. The main differences were in terms of the ozone demand and filtered water characteristics. Performance between the two ozonation modes is summarized as follows: • Settled water turbidity was comparable. • All bromate levels were non-detect for both ozonation modes. • Pre-ozonation exhibited a higher ozone demand compared to intermediate ozonation during typical operating conditions, and the difference in demand between the two ozonation processes increased with increased turbidity during the spiking study. On average, intermediate ozone demand ranged between 0.2 and 0.5 mg/L and pre-ozonation demand ranged between about 0.4 and 0.6 mg/L. • With pre-ozonation, the filters had higher clean bed head loss (CBHL) over time than their paired filters with intermediate ozonation.

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• Both ozonation modes produced low filter effluent particle levels surpassing the water quality goals for particle counts and log removals. • Average TOC removal was about 5 percent higher with pre-ozonation. • Pre-ozonation and intermediate ozonation followed by filtration significantly reduced chlorine demand and decay (CDD) compared to existing treatment, with the greatest benefit occurring during the free chlorine contact period. • Results from simulated distribution system (SDS) testing indicated that DBPs could be reduced significantly from present levels using conventional treatment with either intermediate ozonation or pre-ozonation.

Filter Performance

Filter performance was evaluated for differing filtration rates and filter media over the entire test regime. Table ES-2 presents the filter profiles evaluated from July 2019 through February 2020. Despite there being many different pretreatment conditions tested, all of the filters had low levels of filter effluent turbidity. All of the filters met PSW’s and OHA’s AWOP water quality goal to have the 95th percentile turbidity in the individual filter effluent be less than 0.1 NTU.

In November, a set of samples was sent to Seattle Public Utilities for sensory analysis, including Flavor Profile Analysis (FPA) and Flavor Rating Assessment (FRA). The five-member panel rated the filtered water to be highly acceptable as everyday drinking water, and it was given a top FRA of 1 on a scale of 1 to 9. No distinct differences were found between samples based on filter media or pre-treatment. In comparison, unfiltered, disinfected water samples collected from PWB’s system received FRA scores ranging between 1 and 4. Overall, filtration is expected to maintain or exceed customer acceptance of the water as indicated by these results.

Table ES-2. Filter Media Designs Operated from July 2019–February 2020 Dual media filter configurations Anth-60 Anth-72 GAC-60 GAC-72 Filter location Filter 5 Filters 1, 6 Filter 2 Filters 3, 4 Range of filtration rates tested (gpm/sf) 6-8 8-12 6-8 8-12 Top layer filter media design Media type Anthracite Anthracite GAC GAC Depth (in.) 48 60 48 60 Effective size (mm) 1.15–1.25 1.25–1.35 1.25–1.35 1.25–1.35 Lower Bottom layer filter media design Media type Silica sand Silica sand Silica sand Silica sand Depth (in.) 12 12 12 12 Effective size (mm) 0.55–0.65 0.60–0.70 0.50–0.60 0.50–0.60 Total filter media design L/d ratio 1,520 1,640 1,490 1,730 Total depth (in.) 60 72 60 72

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Filter Media Type Through the piloting effort, filter media type, filter media effective media size, and filtration rates were assessed. Table ES-3 provides a high-level comparison of anthracite and GAC filter media performance between June 2019 and February 2020. Filter effluent from filters containing GAC media had lower levels for organic constituents and DBPs compared with the anthracite media filters. However, the anthracite filters had good organics removal as well and demonstrated improved filter productivity with higher UFRVs compared to the filters with GAC media.

Table ES-3. Filter Media Comparison Summary Filter Factor Units Anthracite GACa Unit Filter Run Volume (UFRV)b gal/sf 7,500–12,000 6,500–10,000 TOC removalc % 45–52 60–62 DBPs: TTHMsd µg/L 6.7–14.1 4.9–10.4 DBPs: HAA5sd µg/L 5.0–10.8 4.4–7.4 a. GAC filter media life was less than 8 months old. b. Range of median (50th percentile) UFRVs from the 12 gpm/sf anthracite or GAC filters from August 20 to December 17, 2019. c. Minimum and maximum TOC removal from the 12 gpm/sf anthracite or GAC filters from August 20 to December 17, 2019. TOC removal based on a comparison of raw water and filtered water. d. Minimum and maximum DBP formation from October and November SDS testing. The DBP information presented is based on a 14-day water age from SDS testing.

The deeper bed GAC filters, operated at 12 gpm/sf, were hindered by their CBHL. It is not certain the causation for the increased CBHL in the GAC filters. The GAC filters had silica sand with a smaller effective size, but the CBHL increased in the GAC filters over time. Biological monitoring demonstrated more biological activity in the GAC media filters compared to anthracite filters. The GAC filters had lower levels of assimilable organic carbon (AOC) and carboxylic acids in the filtered effluent and higher media adenosine triphosphate (ATP) levels. Given the fact that filtration performance was better in the anthracite filters, the anthracite filters had good organics removal, and the anthracite filters were less expensive, it was recommended that the GAC media be swapped with additional anthracite media to allow for more scrutiny testing of the effective size, media depth, and filter loading rates. All six filters were re-built in February 2020 to allow for testing of three different anthracite media profiles (two of which were identical or similar to the anthracite media profiles tested initially). These three anthracite media profiles are specified in Table ES-4.

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Table ES-4. Filter Media Designs Operated from February 2020–June 2020

Dual media filter configurations Anth-60 Anth-66 Anth-72

Filter location Filters 1, 6 Filters 2, 5 Filters 3, 4 Range of filtration rates tested 6-12 6-12 6-12 Top layer filter media design Media type Anthracite Anthracite Anthracite Depth (in.) 48 54 60 Effective size (mm) 1.05–1.15 1.15–1.25 1.25–1.35 Bottom layer filter media design Media type Silica Sand Silica Sand Silica Sand Depth (in.) 12 12 12 Effective size (mm) 0.50–0.60 0.55–0.65 0.60–0.70 Total filter media design L/d ratio 1,660 1,650 1,640 Total depth (in.) 60 66 72

Filtration Rate

All of the filter media profiles tested met performance goals at filtration rates up to their design values. A filtration rate comparison trial was performed where each filter design was tested at the same loading rate. It found that each of the filter media profiles will meet filter effluent performance targets and water quality goals for all of the four filtration rates tested: 6, 8, 10, and 12 gpm/sf. Filter media designs intended for 8 gpm/sf may not be viable for extended periods of operation at 12 gpm/sf due to short run times and high CBHL that limits productivity.

Organics removal was comparable for the anthracite filters at filtration rates of 8, 10, and 12 gpm/sf. When comparing filters operated at their design filtration rate, TOC removals (from raw water to filtered water) ranged from 32 to 55 percent, with no noticeable trend based on filter or filtration rate. Color was removed to below the method detection limit for all filters. Turbidity Spiking Study During the turbidity spiking study, the raw water turbidity was operated for 30 hours at approximately 20 NTU comparing conventional treatment with intermediate ozonation in Train 1 and pre-ozonation with conventional treatment in Train 2. During the last hour of the spiking test, the raw water turbidity was increased to approximately 100 NTU as a stress test. During this stress test, the settled water turbidity never exceeded 10 NTU and the filter effluent quality was exceptional and consistent with typical pilot filter effluent quality, with extremely low turbidities (<0.05 NTU) and low single-digit particle counts. Filter productivity surpassed the desired UFRV goal of 10,000 gallons per square foot (gal/sf) for all filters.

Pilot influent particle counts increased by an order of magnitude during the turbidity spiking study compared to normal influent levels in both organism surrogate ranges. Average log removals comparing raw water to filtered water were quite high; 3.7-logs for particles of 3 to

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5 µm and 4.2-logs for particles of the 5 to 15 µm size range. Comparable filter effluent quality was seen between the two filters tested (48 inches of 1.1 millimeter (mm) anthracite with 12 inches of 0.55 mm silica sand, and 60 inches of 1.3 mm anthracite with 12 inches of 0.65 mm silica sand).

The turbidity spiking study demonstrated the resilience of these treatment trains, as well as their ability to produce exceptional filtered water quality.

Design Considerations

The pilot provided a great opportunity to inform the design of the full-scale Filtration Facility. Under the charge neutralization conditions tested, it was observed that coagulation was sensitive to chemical dosing, and that small changes in coagulant and coagulant aid dosing could reduce coagulation performance. It is recommended that the coagulant and coagulant aid chemical feed systems within the Filtration Facility be designed to control chemical dosing to increments of a tenth of a mg/L, and the Filtration Facility be configured to provide supplemental alkalinity prior to coagulation.

Settled water turbidity was not the best indicator of pretreatment for typical raw water quality. An SCM and zeta potential analyzer were very beneficial to optimize pretreatment and are therefore recommended as tools for operators to use at the future Filtration Facility. Online instrumentation was sensitive to the low alkalinity source water. Care should be taken in selection of online analytical equipment for monitoring pH. Advancements in technology have occurred and will continue to occur during the design of the Filtration Facility. Therefore, the most appropriate online instrumentation for monitoring pH, turbidity, and particle counts should continue to be assessed. The pilot can continue to serve as a tool to evaluate online instrumentation through demonstration testing.

Filter aid polymer was found to be important for controlling particle breakthrough in the filters during all seasonal conditions. While there were occasions when the filters retained particles well without filter aid, performance was inconsistent. Feeding excess filter aid will increase the rate at which head loss develops in the filters, so filter aid usage must balance particle control versus head loss accumulation rate. Due to equipment limitations, the lowest filter aid dose tested during this pilot study was 0.008 mg/L, at which point particles were still well controlled. The minimum filter aid feed dose at which point particles are not well controlled was not determined during this study. It is recommended that filter aid storage and feed facilities be included in the design of the Filtration Facility with the capability to control dosage to the thousandth of a mg/L (0.001 mg/L) and turndown the dose to at least as low as 0.008 mg/L.

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The pilot study found that filter aid dosing needs to be balance minimizing head loss accumulation and maximizing the time before turbidity breakthrough. If operations are controlling filter effluent turbidity and particle counts, the rate of head loss accumulation in the filters is the primary mechanism controlling filter productivity. This is particularly important if a lower terminal head loss threshold is selected for full-scale design. The pilot study used a head loss trigger of 12 feet. The impact of reducing this head loss threshold to 10 feet was investigated during the filtration rate comparison trial. While testing found that the filters could meet productivity goals at a terminal head loss threshold of 10 feet, lowering the terminal head loss threshold from 12 feet to 10 feet reduced filter productivity by 15 to 33 percent as measured by UFRV.

Filter CBHL increased over time and required more vigorous backwashes and chlorine soaks periodically. Increases in CBHL appeared to be related to oxidizable material in the underdrain, additional biogrowth, and/or higher-than-necessary doses of filter aid. The pilot underdrains are not what will be installed full-scale so this may be an area where the pilot performance will vary from full-scale. Regardless, the ability to dose a high chlorine residual in the backwash is recommended for filter maintenance should the need arise.

Regulatory Considerations for OHA

This Report fulfills the Bilateral Compliance Agreement (OHA 2017) requirement to complete a pilot study. This Report presents documentation to request approval for high filtration rates exceeding 6 gpm/sf for deep bed (≥60-inch media) filters. Multiple filter configurations were tested for their ability to meet turbidity standards equivalent to water produced by standard filter loading rates. Tested filter configurations are summarized in Table ES-5. The highest filtration loading rate for which each filter configuration was demonstrated to meet effluent turbidity criteria are shown. Additionally, the highest loading rate for which each configuration met other criteria, including particle count removal and unit filter run volumes, are also shown. Based on water monitoring results for Cryptosporidium levels, the Bull Run source is classified as Bin 1, and therefore, no additional treatment is required for filtered systems per the LT2 Rule. It is requested that each of the conventional filtration configurations listed below in Table ES-5 be approved at the designated filtration loading rate listed for each media design. These configurations will provide a minimum of 2.5-log removal for Giardia and 2-log removal for Cryptosporidium. The specific filter media configuration selected for use in the future Filtration Facility will be recommended in subsequent future design reports and plans. The filter media design will be based on one of the filter media designs listed for OHA approval in Table ES-5.

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Table ES-5. Filter Media Designs for OHA Approval Filter media configurations Anth-60 Anth-60 Anth-66 Anth-72 GAC-60 GAC-72 Performance assessment Proposed approval filtration rate 8 8 10 12 8 12 Maximum filtration rate tested that achieved 12a 8 12a 12 8 12 desired turbidity goal Maximum filtration rate that achieved desired 10a 8 12a 12 8 12 UFRV goal Top layer filter media design Media Type Anthracite Anthracite Anthracite Anthracite GAC GAC Depth (in.) 48 48 54 60 48 60 Effective size (mm) 1.05–1.15 1.15–1.25 1.15–1.25 1.25–1.35 1.25–1.35 1.25–1.35 Bottom layer filter media design Media Type Silica Sand Silica Sand Silica Sand Silica Sand Silica Sand Silica Sand Depth (in.) 12 12 12 12 12 12 Effective size (mm) 0.50–0.60 0.55–0.65 0.55–0.65 0.60–0.70 0.50–0.60 0.50–0.60 Total Filter Media Design L/d ratio 1,660 1,520 1,650 1,640 1,490 1,730 Total Depth (in.) 60 60 66 72 60 72 a. Filtration rates evaluated during filtration rate comparison trial.

Direct filtration options are not being considered at this time for the full-scale Filtration Facility. However, the pilot results demonstrate that such a process configuration meets filter effluent water quality goals under low turbidity raw water conditions.

This Report documents benefits and explores options for including oxidants in the treatment train. Ozonation is studied in this report as pre-treatment to enhance other processes and no inactivation credit for pre-filtration disinfection is being requested. The specific oxidants and locations within the process train will be proposed in subsequent design documentation.

Finished water disinfection demand and residual decay and DBPs were investigated with this study based on the assumption that post-filtration treatment would continue to include a free chlorine contact period followed by chloramination for secondary disinfection and pH and alkalinity adjustment for corrosion control. A specific final disinfection approach will be proposed in subsequent design documentation. Bench-scale corrosion control and coupon studies are currently being conducted to inform the design of corrosion control treatment systems. Study results and requests for approval of corrosion control treatment for the Filtration Facility will be submitted separately.

The remainder of this report is dedicated to detailed discussions and analysis of the pilot test results. The sections document and support the recommendations and conclusions presented herein.

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1.0 Introduction

This Final Pilot Study Report (Report) describes the pilot testing that was conducted on the Portland Water Bureau’s (PWB’s) Bull Run Supply to assist PWB in transitioning to a new greenfield water filtration facility, referred to as the Bull Run Filtration Facility (Filtration Facility). This Report covers the 12-month pilot study testing period from June 2019 through June 2020. The pilot testing was focused on the evaluation of pretreatment ahead of granular media filtration and granular media filtration itself.

The pilot study is part of the overall Bull Run Treatment Program to meet the requirement of providing pilot study results to the Oregon Health Authority (OHA) by November 30, 2020 (2017 Bilateral Compliance Agreement between OHA and PWB [OHA 2017]). One goal of the pilot study was to inform a proposed treatment approach and design for the Filtration Facility, which is scheduled to be in service by 2027. Predesign efforts overlapped with the final 6 months of the pilot study, allowing for collaboration between teams.

In preparation for the pilot study, the 2019 Pilot Plant Work Plan (Work Plan) was prepared detailing the tasks to be completed during the year-long pilot study. The Work Plan was reviewed by OHA in April 2019 and finalized in May (BC 2019). The Work Plan provided a framework for the pilot testing, including an overview of the testing schedule, pilot plant location and site development, and equipment operation, and the plan for water quality data collection. In April 2020, the Interim Pilot Study Report was submitted to OHA. The Interim Pilot Study Report described the pilot testing completed from June 2019 to October 2019 along with a tentative schedule for testing planned through June 2020. Based on operational findings and pilot testing results, the pilot testing schedule was adjusted as needed.

1.1 Background

The pilot study evaluated several treatment approaches including, but not limited to, oxidation (ahead of filtration), conventional filtration, direct filtration, filtration media type, filtration media depth, and filtration loading rates. Pre-ozonation and intermediate ozonation were tested for the ability to improve filtration performance and to evaluate how ozonation followed by biofiltration impacts the removal of natural color, organics, inorganics, and disinfection by- product (DBP) precursors. Pre-chlorination was also evaluated during the pilot study to compare filtration performance and removal of organics to pre-ozonation and intermediate ozonation. This study also assessed each specific unit process with respect to removal of particulates, organics, and the treatment process train’s overall ability to comply with current regulatory requirements and guidance from Partnership for Safe Water (PSW) Phase IV Performance Goals (PSW 2014) and OHA’s Area Wide Optimization Program (AWOP). Furthermore, the study was completed over 12 months to evaluate high-rate filtration performance across seasonal variation in raw water quality. Within the 12-month pilot study,

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Simulated Distribution System (SDS) testing was also completed along with a simulated turbidity event with the turbidity spiking study completed.

1.2 Pilot Plant Study Objectives

The main objectives of the pilot study were to: • Inform treatment process selection for the Filtration Facility along with a broader decision- making, • Support development of a sound, buildable, and operable basis of design for the Filtration Facility that meets regulatory requirements, • Inform design parameters and seasonal operating parameters, • Evaluate data for consistency and potential future considerations of PSW/OHA’s AWOP, and • Serve as an educational tool for engineers and operators, and engagement in treatment process understanding.

The pilot study helped to inform the following design criteria: • Pre-oxidant type, dosing location, contact time, and dose, • Alkalinity and pH adjustments ahead of coagulation, • Coagulant and coagulant aid type and dose range, and addition points for coagulant aid, • Filter aid type and dose range, • Filtration rate, • Unit filter run volume, • Filter media type, effective size, and bed configuration (size and depth), • Primary and secondary disinfectant demand with free chlorine as the primary disinfectant and chloramines as the secondary disinfectant, and • Residual management strategies.

1.3 Test Conditions Summary

Figure 1-1 summarizes the key testing scenarios conducted from June 2019 through June 2020 to investigate filtration design, pretreatment approaches, and meet the study objectives. For each test scenario, the high-level test conditions are included along with the test duration presented in this report. The rest of this section describes the testing scenarios in general. Specific conditions for each testing scenario are presented in Sections 5 through 7 with the detailed findings from that testing.

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Figure 1-1. Summary of pilot testing from July 2019 through June 2020

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Prior to start-up of the pilot plant, bench-scale testing was conducted including jar testing to evaluate coagulants along with coagulant aid and filter aid. PWB, in collaboration with Brown and Caldwell (BC) and Confluence Engineering, conducted jar testing on water collected in December 2018, March 2019, and April 2019. In addition, bench-scale ozone testing was conducted by BC and University of Colorado on raw water collected on March 1, 2019, to inform start-up conditions for the ozone module and to understand ozone demand and decay behavior.

The pilot plant equipment was delivered in early May 2019. The pilot plant consists of two treatment trains, each containing treatment modules for ozonation, flocculation/ sedimentation, and filtration. The filtration module has six filter columns. Three filter columns were operated in parallel and loaded with anthracite or granular activated carbon (GAC) media over sand.

The pilot plant was wet-tested starting in late May 2019, following the pilot plant equipment’s arrival, to check for leaks and functionality. The month of June consisted of start-up and commissioning. Continuous operation officially started on July 1 with a period of coagulation testing and selection, which lasted through mid-August.

Initially, the filters were operated at a filtration rate of 6 and 8 gallons per minute per square foot (gpm/sf), as four coagulants were narrowed down to two. As start-up continued over the summer season, the filtration rates were ramped up to 12 and 8 gpm/sf for the selection of the coagulant to continue for the majority of the pilot testing period.

Once the coagulant selection was complete, an oxidation investigation was started with an evaluation of pre-ozonation. Over the following month, an initial trial of direct and conventional filtration was conducted, followed by the start of a more detailed comparison of pre-oxidants with an evaluation of pre-ozonation and pre-chlorination. Pre-chlorination and pre-ozonation testing continued into early 2020.

During the first 6 months of operations, GAC media were compared with anthracite media. PWB decided to replace the GAC filters with anthracite media in early February (plant shutdown from February 3 to February 18, 2020). Testing with the new media started with both trains in the pre-ozonation mode to establish a new baseline.

An evaluation of pre-ozonation and intermediate ozonation was conducted in March through mid-May. During this test period, the ozone contact time was lowered from 13 minutes to 8 minutes to test performance at the full-scale design condition, based on input from the Design Team. When ozonation was in service, it was tested at the reduced ozone contact time for the remainder of the study.

Starting in mid-May, a detailed filtration rate comparison study was conducted over a 2-week time period to test the filter media designs at similar filtration rates starting with testing all three filter configurations at 10 and 12 gpm/sf, and then testing all three filter configurations at 8 and 6 gpm/sf. Both trains were operated with pre-ozonation during this trial.

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Following the filtration rate comparison, a turbidity event was simulated to test the pilot beyond typical operating conditions. The spiking solution was created using native soil from the Bull Run Watershed that was assessed and determined to be indicative of the type of soil that would stay suspended in the reservoir following a storm event. The spiking solution was able to achieve a pilot influent turbidity level of approximately 20 nephelometric turbidity units (NTU) for a duration of 30 hours, including a brief spike of turbidity up to 100 NTU. The spiking target of approximately 20 NTU was selected to simulate a turbidity event that might follow a severe storm in the watershed, but was not intended to represent a catastrophic event.

The final testing period involved testing direct filtration with intermediate and pre-ozonation. During this trial, chemical dosing was adequate and determined to be representative of the expected operating conditions.

In addition to the pilot testing, SDS testing was performed throughout the 12-month pilot testing period to evaluate the effect of filtration and various pretreatment approaches on the formation of DBPs and chlorine demand and decay (CDD), with free chlorine as the primary disinfectant and chloramines as the secondary disinfectant. Samples were taken from the existing distribution system and raw water for the SDS testing to compare performance to the existing treatment approach. When possible, SDS testing was conducted in conjunction with PWB’s DBP compliance sampling.

1.4 Water Treatment Goals

The pilot study treatment goals and benchmarks are presented in Table 1-1 , which provides the regulatory requirement (if one exists) for the given parameter, and the corresponding pilot study operational goal. The operational goals for turbidity are based on PSW Phase IV Performance Goals (PSW 2014) and OHA’s AWOP.

The settled water quality goal reflects the fact that the source water turbidity is typically less than 1 NTU and through addition of treatment chemicals (mainly a primary coagulant), turbidity is expected to increase through the flocculation/sedimentation process. A common surrogate for monitoring Cryptosporidium and Giardia removal occurrence are particle counts. Particle counters measure the number of particles in solution for a designated particle diameter. By setting the particle diameter to sizes characteristic of specific microorganisms, particle counts can be used as a surrogate to demonstrate Cryptosporidium oocysts (3- to 5-micrometer [µm] diameter) and Giardia cysts (5- to 15-µm diameter) removal.

When source water particle concentrations are low, it is often difficult for treatment processes to attain 2- to 2.5-log particle reductions even though excellent finished water clarity is being achieved (Gong et al. 1993; Yorton et al. 1993). Because log removal is assessed based on the difference between the particle counts of the raw water and filter effluent, the magnitude of log removal that can be demonstrated is limited by the number of particles in the source water. For example, it is necessary to have at least 500 particles/mL in the raw water to mathematically demonstrate 2.5-log removal with 1 or greater particles in the filter effluent and requires a filter effluent particle count of ≤5 particles/mL to demonstrate 2-log removal.

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To overcome this concern, a literature review was conducted to determine if an absolute limit on filter effluent particle counts could be established to assess filter performance given the low raw water particle count levels. There is limited literature on recommended particle count limits, but a particle count limit of less than 50 particles per milliliter (particles/mL) in the 5- to 15-µm range was considered based on LeChevallier and Norton (1992). LeChevallier and Norton’s study found that the occurrence of parasites in plant effluent samples could be related to particle counts greater than 50 particles/mL for particles sized greater than 5 µm (LeChevallier and Norton 1992). A similar particle count limit for the size range related to Cryptosporidium oocysts (3 to 5 µm) was not established in the plan because this size range was not included in LeChevallier and Norton (1992) nor was a similar relationship between Cryptosporidium oocyst occurrence and particle counts found in the literature. The LeChevallier and Norton study evaluated three water treatment plant sites. One site was characterized as having low-turbidity, pristine source water with turbidity generally between 0.3 and 0.5 NTU (Site 3). The study found much variation in filtered water particle count levels with some sites showing as much as 1,000-fold decrease in particle count levels (LeChevallier and Norton 1992). Filtered water particle counts ranged from less than 10 to 850 particles per mL for the pristine site, Site 3 (LeChevallier and Norton 1992).

Organics removal was evaluated through each treatment process and is discussed in the subsequent sections. Enhanced coagulation to remove organics is required if the annual total organic carbon (TOC) levels in the raw water exceed 2.0 milligrams per liter (mg/L). For PWB’s water supply, raw water annual average TOC levels have been less than 2.0 mg/L historically, and averaged 0.95 mg/L for the 12 month pilot study operational period. Based on the historical and most recent TOC levels, enhanced coagulation is not required for the full-scale Filtration Facility, and therefore was not pilot tested. The water quality goals related to DBPs were to reduce total trihalomethanes (TTHMs) and the sum of five haloacetic acids (HAA5s) to be below half of their respective maximum contaminant levels (MCLs).

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Table 1-1. Pilot Study Water Quality Goals and Performance Benchmarks Regulatory Parameter Location Operational Goalb Comments on Operational Goal Requirementa Overview of PSW and OHA’s AWOP Program: ≤ 2.0 NTU, 95% of monthly • ≤ 1.0 NTU, 95% of the time when Settled waterc No requirement samplesd source turbidity ≤ 10 NTU, and • ≤ 2.0 NTU, 95% of the time when source water turbidity > 10 NTU. Turbidity Operational goal matches PSW Phase IV ≤ 0.3 NTU, 95% of ≤ 0.10 NTU, 95% of the Performance goal; OHA’s AWOP operational the monthly filter run time goal is below LT2 Microbial Toolbox credit Individual filter samplesf effluent (FE)e of 0.15 NTU. ≤ 1 NTU at any ≤ 0.30 NTU, 100% of the Operational goal matches PSW Phase IV timef filter run time Performance Goal; OHA’s AWOP. < 50 particles/mL at 5– Particle count goals are surrogates for Individual FEe 15 µm, 95% of the Cryptosporidium and Giardia removal. operational time or Particle counts No requirement Individual FEe 2.0-log removal from raw Particle count goals are surrogates for compared to water for 3–5 µm and 2.5- Cryptosporidium and Giardia removal; raw log removal for 5–15 µmg assumes sedimentation in operation. MCL = 80 ≤ 40 µg/L for chosen TTHM SDS micrograms per treatment scheme based MCLs based on locational running annual liter (µg/L) on DBP SDS testing average (LRAA) of samples collected in distribution system; operational goal (half ≤ 30 µg/L for chosen MCL) is also a trigger for reduced DBP HAA5 SDS MCL = 60 µg/L treatment scheme based monitoring. on DBP SDS testing Minimum Unit > 6,500 gallon/sf-run, 95% Backwash based on turbidity, head loss, and Filter Run h of the operational time run time triggers; operational goal is based Volume (UFRV) Individual filter No requirement on estimated minimum to meet water > 10,000 gal/sf-run, 95% of Desired UFRV production goals. the time Operational goal based on wanting to Filter-to-waste ≤ 5% of total UFRV, 95% of FTW No requirement achieve an filter efficiency of at least 95% (FTW) Cycle the operational time during filter operations. a. Regulatory requirement meets federal and state requirements. b. The operational goal is modeled from PSW and OHA’s AWOP and is an internal PWB goal, not based on regulatory requirements. c. Applicable when operating in conventional filtration mode. d. Optimal turbidity will be determined based on producing filterable floc. Settled turbidities greater than 1 NTU were often required even when raw water turbidity was less than 10 NTU to achieve filtration goals. e. Individual FE samples will be analyzed continually and recorded every 5 minutes. f. Regulatory requirement is based on combined filter effluent (CFE). Pilot study monitoring based on individual FE. g. When operating in direct filtration mode, 2.0-log removal from raw water for 3 to 5 µm range and 2.0-log removal for 5 to 15 µm range. h. The minimum UFRV is based on a filter loading rate of 12 gallons per minute (gpm) per square foot (sf) and a desired plant production of 145 million gallons per day (mgd) with 8 filters and 1 filter out of service.

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2.0 Pilot Plant Configuration

Based on a collaborative pilot design process between BC’s treatment experts, PWB staff, and the Technical Advisory Committee (TAC), the following treatment processes were selected for the pilot study in a dual train configuration: • Rapid mix, • Flocculation alone (direct filtration), • Flocculation and sedimentation (conventional filtration), • Ozonation (pre-ozonation and intermediate ozonation), as well as pre-chlorination, and • Granular media filtration

Figure 2-1 shows the process flow diagram for the pilot plant facilities including two treatment trains in parallel (Train 1 and Train 2). Each treatment train consists of a flocculation- sedimentation, ozone, and filtration module, with the ability to compare direct and conventional filtration as well as compare different coagulation, flocculation, and/or or clarification parameters simultaneously. Conventional filtration includes four discrete unit processes: rapid mix for chemical coagulant dispersion, flocculation, sedimentation, and filtration. Direct filtration is the same process train but with the sedimentation process bypassed. Either treatment train can include oxidation using chlorine or ozone, fed either prior to coagulation (pre-oxidation) or immediately prior to filtration (intermediate oxidation). The ozone unit was configured so that pre-ozonation and intermediate ozonation could be tested in either train. Three filters per train, for a total of six filters, were available to test different media configurations.

The filtered water (i.e., effluent from the six filters) was sent to a backwash storage tank to serve as a backwash water source. Wash water, filter-to-waste, and solids residual from the sedimentation process were managed by an equalization basin followed by liquid-solids separation in a large settling tank, similar to a gravity thickener, referred to as the solids handling system. The waste process, including the equalization basin, were in place to meet discharge requirements and were not tested during this pilot study.

The pilot is configured so that each upstream process operates at a higher rate than downstream processes, to ensure an adequate supply of flow to each process. The excess water overflows to waste lines that were directed to the solids handling system. Excess filtered water was sent to the solids handling system via an overflow in the backwash storage tank. Effluent from the solids handling system was ultimately discharged to the Bull Run River and monitored for discharge characteristics and requirements.

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Figure 2-1. PWB pilot plant dual train process flow diagram Throughout testing, chemicals were dosed by train, with the exception of filter aid. Filter aid was dosed to individual filters when operations permitted.

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The settled solids (i.e., sludge) accumulate and thicken in the settling tank. Solids from the settling basin were pumped out by a vacuum truck for off-site disposal as needed. When chlorine was used as a treatment chemical to evaluate chlorination, effluent from the settling tank was routed through a dechlorination unit (GAC contactor) prior to discharging to the Bull Run River. The solids handling system was designed to handle the pilot wastes but does not mimic a full-scale solids handling system, and therefore, will not inform full-scale design directly.

2.1 Flocculation and Sedimentation The flocculation-sedimentation unit included a three-stage rapid mix system, three-stage flocculation system, and a sedimentation basin with removable settling plates. Figure 2-2 shows the front and back side of the Flocculation-Sedimentation 1000 (Floc/Sed 1000) module at the pilot plant. The rapid mix, flocculation, and sedimentation processes were operated using the control panel’s human-machine Interface (HMI). Adjustable variable speed mixers were provided for individual rapid mix stages and the tapered flocculation stages, allowing for the adjustment of velocity gradients in the mixing vessels.

Figure 2-2. Intuitech flocculation-sedimentation module 1000 (model S300) at the pilot plant Left: Shows the side of the module with viewports into the flocculation and sedimentation basins. Right: Shows the side of the module with the instrumentation, chemical tanks, and HMI.

The flocculation/sedimentation module could be operated in either direct or conventional filtration mode. There was also an option to bypass individual cells of the three-cell flocculation system to vary flocculation detention time. Detention times could also be varied by modifying the inlet flow.

Sedimentation surface loading rates (SLRs) were varied by physically adding up to 24, or removing as many as 22, inclined plate settlers to affect hydraulic unit loading, allowing different SLRs to be tested.

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Coagulant and coagulant aid chemicals were dosed at the rapid mix system to facilitate colloidal destabilization, but could also be added to each stage of flocculation, if desired. Coagulant and coagulant aid were flow paced for this study and sodium bicarbonate was flow paced for alkalinity adjustment.

2.2 Ozonation Pilot Module

The ozonation pilot module (model Z300), shown in Figure 2-3, consisted of two contact chambers and two feed pumps. The module had the flexibility to run in series or parallel depending on the objectives of the study. The ozone generator was air-cooled with an integral oxygen concentrator for creating ozone from ambient air. Each contact chamber contained over-under baffles with five contact chambers cells. Ozone could be applied through a fine bubble diffuser at any one of these three locations: chamber inlet, second chamber cell inlet, or third chamber cell inlet. The ozone gas feed to the chamber inlet was controlled by an automatic proportional-integral–derivative (PID) flow control. Four chemical feed systems were located at the ozone module for primarily dosing additional oxidants and oxidant quenching agents.

Figure 2-3. Intuitech ozonation module (model Z300) at the pilot plant Left: Shows the side of the module with sample ports throughout the ozone contact chamber cells. Right: Shows the side of the module with the instrumentation, chemical tanks, and HMI.

The ozone module was also used for dosing chlorine for prechlorination. Chlorine was dosed in the chemical injection port immediately prior to the contact chamber. The contact chamber served as the contact time for the chlorine. A quenching agent, calcium thiosulfate, was periodically dosed in the chemical injection port downstream of the contact chamber to quench chlorine or ozone residual.

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2.3 Filtration Pilot Module

Figure 2-4 shows the Intuitech six-filter module (model F300) at the pilot plant. The module included six filter columns with individual feed pumps, a backwash system, and an air scour system. Each filter operated independently with the exception of backwashing: only one filter could be backwashed at any given time. Filter backwashing was controlled manually or initiated automatically based on run time, head loss, or effluent turbidity measurement setpoints. More information on filter backwash setpoints is provided below in Section 2.3.1. In addition, the module provides nine chemical feed systems for the ability to feed flow-paced filter aid, pre- oxidants, or reducing agents to all six filters individually, to the filter inlet header, to the filtered water sent to the backwash tank, or the backwash supply water.

Figure 2-4. Intuitech 6-column filtration module, model F300 at the pilot plant

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2.3.1 Filter Media Configurations

The filter columns were each 15-ft tall and could accommodate up to 112-inches of granular media. Various configurations of media were installed in May 2019, as shown in Table 2-1. All six filters were rebuilt with new media in February 2020, as indicated in Table 2-1. The filters were primarily operated as biologically active filters for the larger part of the pilot study period; oxidant residuals were quenched prior to the filter inlet, with the exception of November 22, 2019 through January 21, 2020 when chlorine was dosed at 1 mg/L and not quenched. While filters were backwashed with unchlorinated water during standard operations, there were a few maintenance backwashes with chlorine to recover head loss.

Table 2-1. Six-Filter Configuration Train Filter number Media type July 2019–February 2020 Media type February 2020–July 2020 4 GAC/sand Anthracite/sand

Train 1 5 Anthracite/sand Anthracite/sand 6 Anthracite/sand Anthracite/sand 1 Anthracite/sand Anthracite/sand

Train 2 2 GAC/sand Anthracite/sand 3 GAC/sand Anthracite/sand

Section 2.3.1.1 provides details on the initial filter media configuration, and Section 2.3.1.2 describes the new filter media configurations implemented in February 2020. The initial filter media consisted of GAC and anthracite filters. A decision was made on the filter media type, and only anthracite media was tested from February through July 2020. An explanation of the reasoning for changing out the filter media part way through the pilot study is provided in Section 7.2

2.3.1.1 GAC and Anthracite Media Configuration (July 1, 2019– February 3, 2020)

The pilot was initially configured with three anthracite filters and three GAC filters (Figure 2-5). Two media configurations were chosen for the high-rate filters: 1. A total media depth of 72 inches for a typical filter loading rate of 10 to 12 gpm/sf, and 2. A total media depth of 60 inches for an typical filter loading rate of 8 to 10 gpm/sf.

Each train had two filters with 72 inches of total media depth, one of which was anthracite with sand and the other was GAC with sand. The pilot was designed this way for a direct comparison of filter media type for a filter operated at the same loading rate and pretreatment scheme. The third filter on each train had a total media depth of 60 inches, and was designed to evaluate lower filtration rates. The 60-inch filter on Train 1 was anthracite, while the 60-inch filter on Train 2 was GAC. This pilot design allowed for a comparison of loading rate and filter media depth for the same filter media type. All filters were dual media filters, with the anthracite or GAC on top of a 12-inch layer of silica sand, shown in Figure 2-5.

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Figure 2-5. Schematic of filter media configuration, July 2019-February 2020 The filter media design and the media sieve analysis are presented in Table 2-2. The media used for the filter columns were sent to AWI Filter, U.S. Inc. (AWI) for sieve analysis to confirm media characteristics. One key design criterion for filtration design is the length to diameter (L/d) ratio. Industry practice is to choose an L/d ranging between 1,500 and 2,000 which is calculated with the following formula:

, = , 𝐿𝐿 𝐵𝐵𝐵𝐵𝐵𝐵 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑ℎ 𝐿𝐿 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 The L/d ratios for the 72-inch filters𝑑𝑑 were 1,6𝐸𝐸𝐸𝐸𝐸𝐸70 𝐸𝐸and𝐸𝐸𝐸𝐸𝐸𝐸 𝐸𝐸1,7𝐸𝐸 𝑠𝑠9𝑠𝑠0𝑠𝑠 𝑠𝑠for𝑑𝑑 10the anthracite and GAC medias, respectively. The L/d ratio for the 60-inch anthracite filter was 1,540, while that of the 60-inch GAC filter was 1,550.

The GAC effective size was expected to be between 1.25 and 1.35 millimeters (mm). GAC media selected for pilot testing was the Calgon Filtrasorb 816. The design effective size for the 72-inch anthracite filters was 1.25 to 1.35 mm. The shorter bed anthracite filter was designed with an effective size between 1.15 and 1.25 mm to achieve an L/d greater than 1,500. The silica sand was designed for each media configuration based on assessing the filter media fluidization behavior and intermixing. Leopold, a Xylem brand, provided the anthracite, and Red Flint provided the silica sand.

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Table 2-2. Filter Media Profile Sieve Results (Specification), July 2019–February 2020 Depth Effective size Uniformity Media type Specific gravitya L/d ratio (in.) (mm) coefficient Filters 1 and 6–Anthracite, total media depth of 72" Anthracite 60 1.3 (1.25 to 1.35) 1.28 (<1.4) 1.64 (1.6 to 1.7) 1,170 Sand 12 0.61 (0.6 to 0.7) 1.45 (<1.4) 2.64 (2.6 to 2.7) 500 Total 72 ------1,670 Filter 2–GAC, total media depth of 60" GAC, Calgon Filtrasorb 816 48 1.26 (1.25 to 1.35) 1.34 (<1.4) 1.39 (1.35 to 1.45) 970 Sand 12 0.53 (0.5 to 0.6) 1.42 c 2.64 (2.6 to 2.7) 580 Total 60 ------1,550 Filters 3 and 4–GAC, total media depth of 72" GAC, Calgon Filtrasorb 816 60 1.26 (1.25 to 1.35) 1.34 (<1.4) 1.39 (1.35 to 1.45) 1,210 Sand 12 0.53 (0.5 to 0.6) 1.42 (<1.4) 2.64 (2.6 to 2.7) 580 Total 72 ------1,790 Filter 5–Anthracite, total media depth of 60" Anthracite 48 1.22 (1.15 to 1.25) 1.31 (<1.4) 1.64 (1.6 to 1.7) 1,000 Sand 12 0.56 (0.55 to 0.65) 1.43 (<1.4) 2.64 (2.6 to 2.7) 540 Total 60 ------1,540 a. Specific gravity was not tested during sieve analysis of new filter media. Specific gravity was provided by media supplier for sample shipped.

Spent GAC media was considered because virgin GAC will exhibit a higher level of organics removal until the adsorptive capacity of the GAC media is exhausted. However, virgin GAC was used because exhausted GAC does not have the mechanical properties (i.e., effective size or uniformity coefficient) described in Table 2-2.

Before starting up the pilot study, virgin GAC was washed in 5-gallon buckets to reduce fines and pH prior to loading media into the pilot columns. Prewashing of anthracite media was not required because it does not increase pH of the initial backwash or initial filtered water.

For the original filter media configuration, filtration rates were tested per filter as follows: • 6 and 8 gpm/sf for Filters 2 and 5 • 8 and 12 gpm/sf for Filters 1 and 6 • 8, 10, and 12 gpm/sf for Filters 3 and 4

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2.3.1.2 Anthracite Only Media Configuration (February 18– June 30, 2020)

In February 2020, the media in all of the existing filters were replaced with new anthracite media as shown in Figure 2-6. As before, the new filters were dual-media filters with anthracite on top of a 12-inch layer of silica sand. Each train was built to target a similar L/d ratio. The three different filter media profiles were as follows: 1. An anthracite filter with a 72-inch total media depth and an actual L/d ratio of 1,670. 2. An anthracite filter with a 66-inch total media depth and an actual L/d ratio of 1,740. 3. An anthracite filter with a 60-inch total media depth and an actual L/d ratio of 1,730.

Figure 2-6. Schematic of filter media configuration, February-June 2020

Media size data for each of the three filter profiles are provided in Table 2-3. The filter media design for Filters 3 and 4 was kept the same as the filter media configuration of Filters 1 and 6 prior to February 2020 (i.e., same effective size and filter media depth). Filters 2 and 5 have the same effective size as the prior Filter 5, but 6 more inches of anthracite media depth were added. Filters 1 and 6 represent a new filter media configuration with a smaller filter media effective size of 1.1 mm. The filter media profile values presented in Table 2-3 are based on AWI sieve results with the design specifications shown in parentheses.

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Table 2-3. Sieve Results (Specifications) for Filter Media Profiles Operated from February–July 2020 Media type Depth (in.) Effective size (mm) Uniformity coefficient Specific gravitya L/d ratio Filters 1 and 6–Anthracite, total media depth of 60" Anthracite 48 1.12 (1.05 to 1.15) 1.38 (<1.4) 1.6 to 1.65 (1.6 to 1.7) 1,110 Sand 12 0.49 (0.5 to 0.6) 1.38 (<1.4) 2.64 (2.6 to 2.7) 620 Total 60 ------1,730 Filters 2 and 5–Anthracite, total media depth of 66" Anthracite 54 1.19 (1.15 to 1.25) 1.33 (<1.4) 1.6 to 1.65 (1.6 to 1.7) 1,150 Sand 12 0.52 (0.55 to 0.65) 1.43 (<1.4) 2.64 (2.6 to 2.7) 590 Total 66 ------1,740 Filters 3 and 4–Anthracite, total media depth of 72" Anthracite 60 1.27 (1.25 to 1.35) 1.37 (<1.4) 1.6 to 1.65 (1.6 to 1.7) 1,200 Sand 12 0.65 (0.6 to 0.7) 1.37 (<1.4) 2.64 (2.6 to 2.7) 470 Total 72 ------1,670 a. Specific gravity was not tested during sieve analysis of new filter media. Specific gravity was provided by media supplier for sample shipped.

After replacement of the media in February, each train contained filters designed for three target filtration rates based on their unique media configuration: • 8 gpm/sf for Filters 1 and 6 • 10 gpm/sf for Filters 2 and 5 • 12 gpm/sf for Filters 3 and 4 Additionally, a filtration rate trial was conducted during which each of the three media configurations were tested at 6, 8, 10, and 12 gpm/sf for multiple runs.

2.3.2 Filter Media Backwash Setpoints

Backwash flowrates were selected to target fluidization at the low backwash rate and 30 percent bed expansion at the high backwash rate, with setpoints changing slightly as water temperatures changed. Table 2-4 shows the backwash initiation criteria and backwash protocol for the filter operations from July 2019 to February 2020. Throughout the pilot study, the backwash/air scour sequence and protocol were kept relatively constant. The sequence was established to end the filter-to-waste cycle when the turbidity dropped below the desired goal. This goal could be adjusted when additional backwash water was needed. Along with turbidity, head loss, and run time, the filters could also be backwashed based on particle counts, but particle counts were never used as a backwash initiation criterion during the pilot study.

The turbidity of the filter-to-waste water was recorded every 5 minutes. Filter-to-waste flows were diverted to the pilot plant waste handling system and not the filtered water/backwash supply tank.

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Table 2-4. Backwash Initiation Criteria and Operation for GAC and Anthracite Media Configuration, July 1, 2019–February 3, 2020 Backwash Initiation Criteria Value Maximum turbidity 0.15 NTUa Maximum head loss 12 ft Maximum filter run time 96 hours Backwash Protocol Step Parameters 1 minute at 3.50 standard cubic feet per minute (scfm)/sf for GAC filters Air scour time and rate 1 minute at 4 scfm/sf for anthracite filters Simultaneous air scour/hydraulic 138 inch fill level at 4 scfm/sf and water at 5 gpm/sf for GAC filters backwash fill level and rate 138 inch fill level at 4 scfm/sf and water at 6 gpm/sf for anthracite filter 5 minutes of water at 10 gpm/sf for GAC filters Low backwash flow time and rate 5 minutes of water at 13.5 gpm/sf for anthracite filter 10 minutes of water at 22 gpm/sf for GAC filters High backwash flow time and rate 10 minutes of water at 29.25 gpm/sf for anthracite filters 5 minutes of water at 10 gpm/sf for GAC filters Low backwash flow time and rate 5 minutes of water at 13.5 gpm/sf for anthracite filter Quiescent settling time 10 minutes Filter-to-waste Minimum filter-to-waste timing of 5 minutes, and until filter effluent turbidity is ≤ 0.15 NTU a. UFRVs will be evaluated using truncated data based on 0.1 NTU and PSW, although the backwash trigger has been set at 0.15 NTU to facilitate additional data collection. Maximum turbidity was 0.2 NTU during initial start-up phase.

When the filter media were replaced in February 2020 and transitioned to all anthracite/sand columns, adjustments were made for the high-rate backwash flow rates so that each high-rate backwash correlated with the anthracite media’s effective size. These flow rate changes are summarized in Table 2-5.

Table 2-5. Adjusted High-Rate Backwash Rate for Anthracite-Only Media Configuration, February 18–June 30, 2020 Filter Adjusted High Backwash Rate Filters 1 and 6 10 minutes of water at 17.5 gpm/sf Filters 2 and 5 10 minutes of water at 19 gpm/sf Filters 3 and 4 10 minutes of water at 20.5 gpm/sf

Air scour and backwash rates were adjusted slightly, as needed, to achieve the desired 30 percent bed expansion at the high backwash flow stage and bed fluidization at the low backwash flow stage as water temperature and viscosity changed throughout the pilot duration. In addition, because of increased clean bed head loss (CBHL) over time, air scour times and high backwash rates were increased to sufficiently clean the beds periodically and target a 40 percent bed expansion. Backwash followed by the start of a filtration run was designed so that it can be completely automated to allow for continuous operation. Note, this pilot study was not intended to focus on backwash optimization.

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2.4 Solids Handling

The primary waste streams from the pilot plant were settled solids from the sedimentation process, overflow from the flocculation and/or ozone process, overflow from the filter backwash tank, and the filter spent backwash water, all of which were routed through a solids handling system prior to discharge to an existing stormwater National Pollutant Discharge Elimination System (NPDES) outfall. The lab sink within the pilot enclosure also generated a periodic waste stream and was treated by the solids handling system. Waste streams managed by the solids handling system contain solids from the raw water including natural organic matter, suspended solids, microorganisms, organic and inorganic constituents, as well as small amounts of coagulant metal hydroxides and polymers from treatment chemicals from settled solids and backwash waste, including process water overflows. The waste streams periodically included low levels of chlorine residual when chlorine was tested as a pre-oxidant.

The solids handling system included a gravity fed buried sump (i.e., an equalization basin) from which waste streams from the pilot plant were pumped to a large settling basin. A 16,000-gallon “Flip Top Weir” tank, 43-by-8-by-10.5-feet in size, was used for the settling basin (Figure 2-7).

Figure 2-7. Rain For Rent settling basin tank at the pilot plant 16,000-gallon flip top weir tank hydraulic capacity based on 4-inch outlet location.

If necessary, solids can be removed as liquid sludge (estimated to be approximately 2 to 3 percent by compaction) by a vactor truck for disposal. Decant liquid flowed from a 4-inch outlet on the side of the settling tank and discharged to the river through a stormwater NPDES discharge location. The requirements surrounding this discharge process are described in Section 2.7. While the full-scale facility will be designed as a zero liquid discharge (ZLD) facility, meaning that treated liquid residuals will be recycled to the facility inlet, the pilot study did not include any evaluation of recycle streams being re-introduced into the processes.

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2.5 Varying Operational Parameters

The treatment chemicals used directly in the pilot treatment process were all NSF-60 approved for potable water consumption and used at doses below the NSF-60 potable water maximum use limit (MUL). Table 2-6 lists the range of these key process parameters tested during the pilot study, including chemical dosage ranges.

Table 2-6. Unit Process Variables, July 2019-June 2020, Excluding Turbidity Spiking Study Variable parameter Type or units Variable range Ozonation Influent flow per train gpm 8.0–10.0 Number of contact chamber cell(s) operating each 3–5 Ozone contact detention timea minutes 8–16 Ozone dosea mg/L 0–2.0 Rapid Mix

Alkalinity dose mg/L as CaCO3 0–75 Number of basin(s) operating each 3 Detention time seconds 15.8–18.8 Velocity gradient (each) seconds-1 200–380 Coagulant type e.g., Alum, Ferric, PACl, ACHb Alum, Ferric, PACl, ACHb 3+ 3+ Coagulant dose mg/L as Al or Fe 0.04–2.08 Coagulant aid (polymer) type Cationic Clarifloc C-359 Coagulant aid (polymer) dose mg/L 0–1 Flocculation Influent flow per train gpm 8.0–9.5 Number of basin(s) operating each 3 Detention time minutes 30–36 Velocity gradient (each, tapered) seconds-1 25–80 Sedimentation Influent water flow per train gpm 8.0–9.5 Detention time minute(s) 22.9–26.4 Settling plates number 12–24 Nominal surface overflow rate (SOR) gpm/sf 1.84–2.06 SLR with plates gpm/sf 0.1–0.3 Sludge flow rate gpm 0.5 Filtration Influent flow per filter gpm 1.5–2.4 Filter aid type Nonionic Clarifloc N-6310 Filter aid dose mg/L 0–0.08 Filtration ratesa gpm/sf 6–12 Empty Bed Contact time (EBCT) min 3.1–7.5c a. Most vital parameters for detailed design. b. Coagulants include: Hydrated aluminum sulfate (alum), polyaluminum chloride (PACl), ferric chloride (Ferric), aluminum chlorohydrate (ACH). c. Filtration contact time includes the filtration evaluation where filters with a total media depth of 60 to 72 inches were operated at a filtration rate of 6 to 12 gpm/sf.

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Throughout jar testing and pilot operations, all chemicals were dosed as mg/L of chemical solids (i.e., accounting for the concentration of the neat chemical). In order to compare different primary coagulants throughout testing, aluminum-based coagulants are represented as mg/L as active aluminum (Al3+) or active iron (FE3+) in this report. The relationship between aluminum- based coagulants is summarized in Table 2-7, based on the concentration of the specific chemicals used for this study. For more extensive conversation factor information for all coagulant and dosages used throughout the jar and pilot testing, please refer to Appendix A.

Table 2-7. Conversion Factors for Aluminum–Based Coagulant Dosages Dose as mg/L Equivalent dose as mg/L as Equivalent dose as mg/L as Equivalent dose as mg/L as Al3+ PACl Alum ACH 1.0 3.89 11.36 3.37

2.6 Water Quality Data Collection

To assess pilot unit operation, staff collected water quality data throughout the study at varying frequencies depending on the parameter. Some parameters were collected to compare against operational goals and performance benchmarks, while others were for process control only.

2.6.1 Comprehensive Water Quality Testing (or Measurement)

During continuous pilot operations from the beginning of July 2019 through the end of June 2020, sampling for a variety of water quality parameters was conducted at different frequencies. Table 2-8 summarizes the parameters measured, the frequency, and the test method, along with the method reporting limit (MRL). The frequency of sampling for some of the water quality parameters, such as dissolved oxygen (DO) and alkalinity, were adjusted during some testing weeks to allow more flexibility in operational time onsite. Chlorine and ozone residuals were also measured to assess oxidant dosage and to confirm operation during pre-oxidation, using the online instrumentation and/or field devices.

All sampling was conducted according to a standard operating procedure (SOP) developed by BC and PWB. Sample filtering for true color, filtered ultraviolet (UV) absorbance at the 254 nm wavelength (UV254), and dissolved organic carbon (DOC) was performed using polyethersulfone (PES) 0.45 micron filters using either a vacuum or syringe apparatus.

For media adenosine triphosphate (ATP) sampling, filter columns were temporarily taken offline, partially drained, and sample taps from the front of the column removed to allow for sample collection at varying depths. The collected samples were then processed according to the SOP for ATP analysis. In addition to media ATP samples, biological activity was assessed using aqueous ATP and the calculated removal of biodegradable organics, such as assimilable organic carbon (AOC) and carboxylic acids.

Bench-scale SDS testing was completed in October, November, April and June to assess how various treatment approaches could impact DBP formation and CDD. During the SDS testing, filter effluent samples were collected and then treated according to the SDS protocol to simulate post-treatment (primary disinfection, secondary disinfection, and corrosion control

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adjustments). Following post-treatment, samples were immediately analyzed for TTHMs, HAA5s, total chlorine, and for additional water quality parameters such as pH, alkalinity, and color. Additional post-treated samples were incubated at a temperature in the range of PWB’s distribution system and analyzed at 7 and 14 days following post-treatment to simulate different water ages. Following the specified incubation period, each sample was analyzed for TTHMs, HAA5s, total chlorine, and additional water quality parameters. The November 2019 SDS test also included a flavor profile analysis (FPA) performed by a trained sensory panel at Seattle Public Utilities. Detailed methods and results of the SDS testing are included in the SDS testing reports in Appendix B and information from the June testing, which occurred during the turbidity spike test, is included in Appendix H.

Table 2-8. Comprehensive Water Quality Parameters and Frequency Typical Parameter Instrument Method MRL Frequency pH 5x/week Hach PHC281 SM 4500-H+B -- DO 5x/week Hach PHC281 Hach 10360 0.10 mg/L 10 mg/L as calcium Alkalinity 5x/week 16900 Digital Titrator Hach 8203 carbonate (CaCO3) True Color 5x/week Hach DR3900 Hach 8025 3 color units (Pt-Co) Apparent Color 5x/week Hach DR3900 Hach 8025 3 color units (Pt-Co) Turbidity 5x/week Hach TU5200 Hach 10258 0.0001 NTU 0.0045 ultraviolet UV 5x/week RealTech UV P200 Meter EPA 415.3 254 254 absorbance (UVA)

Dissolved UV254 5x/week RealTech UV254 P200 Meter EPA 415.3 0.0045 UVA

TOC 3x/week Shimadzu TOC-VWP SM 5310C 0.30 mg/L

DOC 3x/week Shimadzu TOC-VWP SM 5310C 0.30 mg/L Inductively coupled plasma mass Fe 3x/week EPA 200.8 5 µg/L spectrometry (ICP-MS) Al 3x/week ICP-MS EPA 200.8 2–8.1 µg/L Mn 3x/week ICP-MS EPA 200.8 0.5 µg/L

Aqueous ATP 2x/month PhotonMaster Luminometer -- 0.2 g ATP/mL AOC, Carboxylic High performance liquid chromatography 2x/month SM 9217B 0.5-4 ug/L Acids (HPLC)/UV Gas chromatography (GC) Tandem Mass TTHMs Seasonally EPA 524.2 0.5 µg/L Spectrometry (MS/MS) HAA5a Seasonally GC Electron Capture Detection (ECD) EPA 552.3 2 µg/L Nitrosamines Seasonally GC-MS/MS EPA 521 2 µg/L Bromate Seasonally Ion Chromatography EPA 317 1 µg/L Media ATP Seasonally PhotonMaster Luminometer -- 100 pg ATP/g Total Suspended Seasonally Gravimetry SM 2540D 1 mg/L Solids (TSS)

Free Chlorine Occasionally Hach SL1000 Hach 10272 0.03 mg/L Cl2 b Ozone Occasionally Hach DR3900 Hach 8311 0.01 mg/L O3 One HAA5 sample was analyzed by Eurofins Eaton Analytical Laboratory via SM 6251B. Ozone reporting limit is an estimated detection limit (EDL) compared to the MRL listed for other parameters.

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2.6.2 Sampling Locations

Sample locations for process monitoring were established between each unit process in order to isolate and evaluate each process. Samples were collected from the following locations: • Raw water inlet, • Oxidation inlet (prior to oxidant addition), • Oxidation contact chamber outlet, • Flocculation outlet, • Settled water outlet, • Filter Trains 1 and 2 inlet (oxidation outlet when operating in intermediate ozonation mode), • Filter effluent (1, 2, 3, 4, 5, and 6), • Sedimentation sludge drain, • Backwash supply outlet, and • Filter sample ports along filter bed column

2.6.3 Online Instrumentation and Zeta Potential

Turbidity, particle counts, head loss, and pH were continuously monitored by online analyzers, and data recorded every 5 minutes. A streaming current monitor (SCM) and zeta potential analyzer also assisted with process optimization. A trial of the SCM was initially investigated and permanently installed in October 2019. A bench-top zeta potential analyzer was trialed during October 2019 and again in April 2020. The zeta potential analyzer was utilized from April 2020 through the remainder of the pilot study period. Further information regarding the SCM and zeta potential relationship can be found in Appendix C.

2.6.3.1 Turbidimeters HF Scientific MicroTOL turbidimeters (model 28052) were located at the flocculation basin inlets for each train, settled water outlets for each train, and at the filter effluent for each filter. Inlet and settled water outlet turbidimeters of each train were fed by a peristaltic pump. The turbidimeters were calibrated monthly. In addition, weekly verifications were conducted to confirm the calibration is still accurate. If the verification failed, the turbidimeters were recalibrated. Cleaning was also an important component of the turbidimeter operation. Initially, the meters were cleaned when needed, and after several weeks of operation, the frequency was increased to more frequent monitoring, cleaning, and verification in order to control drift.

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2.6.3.2 Particle Counters Chemtrac Model PC6 particle counters were located on Floc/Sed 1000 influent and settled water outlet, as well as on the effluent of each filter column. The following nine size ranges were set for each particle counter: • 2 to 3 µm • 3 to 5 µm (Cryptosporidium oocysts diameter) • 5 to 7 µm (Cryptosporidium oocysts and Giardia cysts diameter) • 7 to 10 µm (Giardia cysts diameter) • 10 to 15 µm (Giardia cysts diameter) • 15 to 20 µm • 20 to 30 µm • 30 to 100 µm • ≥ 100 µm

When pre-ozonation was used on Train 1, the Floc/Sed 1000 influent was no longer representative of raw water; this occurred from January 27 to March 10, 2020. To measure particle counts on true raw water, the Floc/Sed 1000 particle counter was fed from a raw water hose during this time period.

2.6.3.3 pH Probes Thermo Scientific AquaSensors DataStick pH probes were located at each flocculation basin inlet and outlet, each settled water outlet, each ozone module effluent, and at each filter train’s effluent. The pH probes were calibrated and verified monthly. In addition, weekly verifications were conducted to confirm the calibration was still accurate. If the verification failed, the probes were recalibrated. The grab samples for pH were found to be more reliable in this low ionic strength water, and the grab sample results for pH are discussed in Section 2.6.1.

2.6.3.4 SCM A CHEMTRAC online SCM was used to guide the coagulant and coagulant aid dose for the coagulation process. A single SCM was installed on the Floc/Sed 1000 module with flexible tubing that allowed the instrument to read from either modules by switching the feed line. The SCM instrument uses a DuraTrac 4 streaming current sensor that measures the alternating current generated by the movement of a piston that drives ionic species and colloidal-sized particles in the sample water through an annulus separating two electrodes. This “streaming current” measures the net ionic and colloidal surface charge of the sample water, which, in this case, was collected immediately downstream of the rapid mix basin of the pilot. Charge is reported as Streaming Current Unit (SCU) with a range of -1000 to +1000, where 0 is neutral. Raw water was used to calibrate the instrument and changes in charge were reported relative to that calibration. As the raw water quality changed throughout the year, variation in readings required seasonal recalibration. The SCM was initially calibrated when installed in November 2019 and subsequently calibrated every 3 to 4 months through pilot operations. Along with the calibrations, the gain was also adjusted and/or the instrument verified as needed.

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2.6.3.5 Zeta Potential Beginning in April 2020, a Zetasizer (NanoZ, Malvern Panalytical) was procured as an additional tool for the pilot. The Zetasizer uses micro-electrophoresis/electrophoretic light scattering technology to measure zeta potential and electrophoretic mobility. The Zetasizer uses voltage to report particle charge, which is an absolute measurement and is, therefore, not influenced by variation from other water characteristics. The Zetasizer is a benchtop instrument, which only provides grab sample readings. This instrument was routinely used, in most cases daily, to provide operational guidance.

2.6.4 Discharge Compliance and Mitigation of Risk to Aquatic Life

In order to comply with the NPDES requirements on the permitted outfall, the pilot discharge was required to meet the following requirements: • Total chlorine residual not to exceed 0.1 mg/L • pH to range between 6.0 and 9.0

Along with NPDES permit discharge requirements, more stringent monitoring requirements were developed with PWB’s Aquatic Life Supervisors Resource Protection Group in order to mitigate risk to downstream aquatic life. Dose limits were established for the treatment chemicals based on a safety factor that is significantly below the aquatic toxicity for each chemical, while still optimal for water treatment. The aquatic toxicity was determined based on the reported LC50, the lethal concentration considered to result in the death of half of the test population after 96 hours of exposure for fish and 48 hours for invertebrates. Minimum chronic toxicity was also checked for the chemicals with an established criteria available. More stringent monitoring requirements developed included the following requirements: • DO levels above 5.0 mg/L • Visual inspection and notification protocol for daily monitoring of fish mortality

Visual inspections of the river for fish mortality and chlorine residual, pH, and DO measurements were completed daily when the pilot was operating. The discharge requirements specific to NPDES were reported monthly to meet the monitoring requirements of the permit. During the pilot study test period described in this Report, the discharges were within the NPDES requirements and goals.

Testing reagents, like N,N Diethyl-1, 4 Phenylenediamine Sulfate (DPD) for free chlorine testing, were disposed of through the Headworks Facility United Site Services waste removal contract. Prior to disposing of pilot waste, the pH was measured and adjusted if necessary, to be within the following limit: pH to range between 5.0 and 11.5.

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3.0 Raw Water Quality Characteristics

Raw water quality characteristics are summarized from July 1, 2019, through June 30, 2020, in the following section. Average monthly and seasonal values, as well as time series plots for key parameters are presented in this section.

The full-scale Filtration Facility is being designed as a ZLD facility with recycle flows returned to the inlet. Although these recycle flows are limited to a fraction of the total inlet flow by the Filter Backwash Recycling Rule, they may have some impact on the inlet water quality that is treated by the full-scale Filtration Facility. The impact from these recycle streams was not evaluated at pilot scale.

3.1 Monthly and Seasonal Overview

Table 3-1 summarizes the pilot raw water quality during the reporting period including average, minimum, and maximum monthly values for turbidity, temperature, alkalinity, pH, total particle counts, TOC, DOC, filtered UV254, and specific UV absorbance (SUVA).

Table 3-2 summarizes the same raw water parameters on a seasonal basis.

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Table 3-1. Average (Minimum–Maximum) Monthly Pilot Raw Water Quality, July 2019–June 2020

Turbidity Temperature Alkalinity c Total Particle Counts TOC DOC Filtered UV254 SUVA Month a b c pH d c c,e -1 c f (NTU) ( ͦC) (mg/L CaCO3) (#/mL) (mg/L) (mg/L) (cm ) (L/mg-m) 0.25 14.1 9.3 7.3 0.73 0.75 0.029 3.8 July ---g (0.22-0.33) (13.6-14.8) (6.7-10.7) (7.0-7.8) (0.71-0.75) (0.71-0.83) (0.026-0.042) (3.4-4.0) 0.31 14.7 9.5 7.2 2,514 0.76 0.85 0.026 3.3 August (0.23-0.56) (14.0-16.9) (7.6-10.7) (6.9-7.7) (1,508-5,602) (0.70-0.81) (0.74-1.2) (0.016-0.036) (2.1-4.7) 0.42 16.0 11.3 7.5 3,836 0.78 0.88 0.032 3.8 September (0.33-0.76) (14.4-17.0) (9.5-12.9) (7.0-7.8) (2,355-6,738) (0.72-0.87) (0.77-1.0) (0.028-0.038) (3.4-4.4) 0.44 13.5 11.9 7.4 3,868 1.1 1.2 0.044 3.9 October (0.37-1.32) (9.8-16.3) (11.1-12.9) (6.8-7.8) (1,489-6,718) (0.89-1.4) (0.90-1.7) (0.030-0.061) (3.2-4.6) 0.29 8.7 11.4 7.5 2,767 1.3 1.3 0.052 4.2 November (0.24-0.97) (7.3-13.7) (10.0-13.1) (7.0-7.8) (2,082-5,963) (1.2-1.4) (1.2-1.4) (0.012-0.06) (3.9-4.5) 0.26 6.6 11.3 7.2 2,811 1.2 1.2 0.051 4.2 December (0.22-0.49) (5.9-10.3) (9.5-13.3) (7.0-7.5) (2,205-6,652) (1.1-1.3) (1.2-1.2) (0.047-0.055) (3.9-4.6) 0.37 5.5 8.3 7.0 3,320 1.2 1.2 0.056 4.7 January (0.22-0.65) (5.2-10.4) (7.2-9.8) (6.8-7.2) (2,269-6,059) (1.1-1.3) (1.1-1.3) (0.048-0.063) (4.0-4.9) 0.54 5.7 7.7 7.2 2,919 0.94 0.93 0.044 4.5 February (0.39-0.72) (5.3-16.5h) (7.7-7.7) (7.1-7.3) (1,434-4,776) (0.92-0.96) (0.89-0.97) (0.041-0.048) (4.4-4.6) 0.40 6.0 7.3 7.2 4,337 0.80 0.83 0.035 4.3 March (0.33-0.47) (5.6-6.8) (7.2-7.3) (7.0-7.6) (1,632-6,747) (0.74-0.91) (0.77-0.89) (0.029-0.04) (3.9-4.6) 0.28 7.1 7.7 7.6 4,294 0.78 0.80 0.033 4.0 April (0.23-0.39) (5.8-8.4) (7.1-8.7) (6.9-7.8) (3,165-6,735) (0.76-0.86) (0.79-0.82) (0.031-0.035) (3.8-4.3) 0.27 9.6 8.0 7.3 3,305 0.91 0.87 0.039 4.6 May (0.24-0.51) (8.1-13.2) (6.7-8.5) (6.9-8.0) (2,065-6,493) (0.83-0.96) (0.53-0.97) (0.033-0.043) (3.6-8.1i) 0.30 11.2 8.7 7.2 2,372 0.97 1.0 0.044 4.3 June (0.25-0.38) (10.2-12.7) (8.4-9.5) (6.9-7.8) (1,462-6,676) (0.91-1.0) (0.95-1.1) (0.040-0.050) (3.6-4.8) Statistics for 4-hour compliance measurements from online turbidimeter at the Headworks. Statistics from combination of Floc/Sed 1000 Inlet and Floc/Sed 2000 Inlet HMI measurements for temperature. Data included between the 1st and 99th percentile.

Monthly statistics for grab samples collected at the pilot inlet for alkalinity, pH, TOC, DOC, and Filtered UV254. Total particle counts include combination of particles in all bin sizes (2-100 µm). Particles counts post-ozonation were excluded from the statistics in the table. Data included between the 1st and 99th percentile. DOC values were on average greater than TOC as a result of interference from filtering the sample.

SUVA = Filtered UV254/ DOC *100. Particle counts in July were unreliable due to issues with the particle counter calibration. Maximum temperature in February occurred due to intermittent operation of the pilot after initial start-up with the new media, resulting in warmer water for a short period of time. -1 SUVA maximum for the month of May occurred on May 28, with a low DOC (0.53 mg/L) and high filtered UV254 (0.043 cm ).

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Table 3-2. Average Seasonal Pilot Raw Water Quality, July 2019–June 2020

Turbidity Temperature Alkalinity c Total Particle Count TOC DOC Filtered UV254 SUVA Month a b c pH d c c,e -1 c f (NTU) (°C) (mg/L CaCO3) (#/mL) (mg/L) (mg/L) (cm ) (L/mg-m) Summer 0.32 14.9 10.1 7.3 3,308 0.75 0.82 0.03 3.6 (July–Sept) (0.22-0.76) (13.6-17.0) (6.7-12.9) (6.9-7.8) (1,508-6,738)g (0.70-0.87) (0.71-1.2) (0.016-0.042) (2.1-4.7) Fall 0.33 9.7 11.6 7.4 3,054 1.2 1.2 0.049 4.1 (Oct–Dec) (0.22-1.32) (5.9-16.3) (9.5-13.3) (6.8-7.8) (1,489-6,718) (0.89-1.4) (0.9-1.7) (0.012-0.061) (3.2-4.6) Winter 0.43 5.8 7.8 7.1 3,814 1.0 1.0 0.045 4.5 (Jan–March) (0.22-0.72) (5.2-16.5h) (7.2-9.8) (6.8-7.6) (1,434-6,747) (0.74-1.3) (0.77-1.3) (0.029-0.063) (3.9-4.9) Spring 0.28 9.1 8.1 7.4 3,423 0.88 0.88 0.039 4.3 (Apr–June) (0.23-0.51) (5.8-13.2) (6.7-9.5) (6.9-8.0) (1,462-6,735) (0.76-1.0) (0.53-1.1) (0.031-0.050) (3.6-8.1i) a. Statistics for 4-hour compliance measurements from online turbidimeter at the Headworks. b. Average from combination of Floc/Sed 1000 Inlet and Floc/Sed 2000 Inlet HMI measurements for Temperature. Data included between the 1st and 99th percentile. c. Average of grab samples collected at the pilot inlet for alkalinity, pH, TOC, DOC, and Filtered UV254. d. Total particle counts include combination of particles in all bin sizes (2-100 µm). Particles counts post-ozonation were excluded from the statistics in the table. Data included between the 1st and 99th percentile. e. DOC values were on average greater than TOC as a result of interference from filtering the sample. f. SUVA = Filtered UV254/ DOC *100. g. Particle counts in July were unreliable due to issues with the particle counter calibration. h. Maximum temperature in February occurred due to intermittent operation of the pilot after initial start-up with the new media, resulting in warmer water for a short period of time. -1 i. SUVA maximum for the month of May occurred on May 28, with a low DOC (0.53 mg/L) and high filtered UV254 (0.043 cm ).

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3.2 Temperature, Alkalinity, and pH

Water temperature, which was measured continuously by an online meter, followed a seasonal pattern with temperatures around 15°C on average in the summer, with a shift to around 10°C in the fall, followed by an additional decrease in winter to 5.8°C. Temperatures warmed again in spring with an average of 9.1°C (Figure 3-1). Throughout the study there were periodic times where the measured water temperature spiked dramatically. These spikes were the result of pilot shutdowns where the water remained stagnant at the pilot intake and was allowed to warm to the temperature of the pilot enclosure. This was most prominent around the pilot start-up after the media change out in February when the pilot operated intermittently for a period, resulting in higher raw water temperatures in February than would otherwise be observed in the true raw water prior to entering the pilot module.

Alkalinity remained low and fairly constant throughout the study, with an increase in the fall through winter seasons measured by daily grab samples (Figure 3-2). There was a gradual increase from summer to fall, with the highest monthly average alkalinity of 11.9 mg/L as CaCO3 in October. Alkalinity remained above 11 mg/L through January, and dropped to an average of 7.7 mg/L as CaCO3 throughout the spring. It remained in the 7 to 8 mg/L as CaCO3 range for the remainder of the study.

Figure 3-3 shows the pH levels measured by daily grab samples throughout the pilot study, which fell within a pH range of 6.8 to 8.0. The monthly averages remained consistent, ranging from 7.0 to 7.6.

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Figure 3-1. Raw water temperature

Figure 3-2. Raw water alkalinity

Figure 3-3. Raw water pH

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3.3 Raw Water Turbidity

Raw water turbidity data are presented in Figure 3-4. Grab sample data collected daily during the work week at the pilot inlet, as well as turbidity measurements from the compliance instruments at the Headworks raw water inlet, reported every four hours are presented. The grab samples were consistent with the Headworks compliance samples throughout most of the testing period.

Figure 3-4. Raw water turbidity on Train 2, July 2019–June 2020

The grab and compliance samples at Headworks gradually increased over time from an average of 0.3 NTU in July to an average of 0.4 NTU in October. The average turbidity remained between 0.3–0.4 NTU until there was an increase in February to an average of 0.5 NTU. Monthly average turbidity decreased back to 0.3 NTU in the spring. Based on historical data from 2007 to 2018 (BC 2020), the seasonal turbidity observed during pilot testing mimics historic seasonal variation.

While there were occasional increases in turbidity during the study above 0.5 NTU, and one 4-hour compliance sample at the Headworks above 1.0 NTU (1.32 NTU in October due to operation of the needle valves in the diversion pool), no natural turbidity events occurred. This is expected given that large fluctuations in turbidity are not common in the Bull Run watershed; only ten shutdown events have occurred since 1986, representing approximately 1.2 percent of the operational time (BC 2020). A turbidity spiking trial (discussed in Sections 5.7, 6.6.4, and 7.3.10) was conducted in June 2020 and tested the pilot under increased turbidity loading.

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3.4 Particle Counts

Particle counts from the Floc/Sed 1000 inlet (Train 1) for the 3–5 µm and 5–15 µm bin sizes, as well as the total particle counts, are presented in Figure 3-5, recorded every 5 minutes from online particle counters. The results represent raw water particle counts, when no oxidant was applied, and post-pre-oxidation particle counts when an oxidant was applied ahead of the floc/sed process. As a result of the particle counter placement, when Train 1 was operating with a pre-oxidant, the particle counts were representative of oxidized water, and not true raw water characteristics.

The effect of ozone on particle counts was of concern to the pilot team because the calculation of log-removal during this time was not representative of true raw water. To avoid this issue, the particle counter was placed on the train that was primarily operated in a non-oxidation mode (Train 1). However, when pre-ozonation was tested side by side on both trains, Train 1 was impacted by pre-ozonation. From January through March, the particle counter sample connection was moved upstream of the ozone module to analyze raw water without the influence of pre-ozonation. However, there was concern about stagnant water in the long hose used to sample the raw water causing lower than expected particle counts and the particle counter was returned to the Floc/Sed 1000 inlet on March 10.

The particle counts were typically representative of raw water. At times the water was pre- oxidized with ozone, which appeared to have lowered the particle counts compared to those in untreated raw water. Furthermore, because the particles in the 3–5 µm and 5–15 µm range were fairly low, the <50 particles/mL effluent criteria generally governed demonstration of surrogate removal. Pre-chlorination, on the other hand did not appear to have a measurable impact on particle counts.

The time periods when the raw water particle counts were measured after the water was oxidized (i.e., pre-oxidation in use) are shown on Figure 3-5, as follows:

• August 20–30, 2019: Pre-ozonation (target dose of 0.5 mg/L as O3)

• September 29–October 11, 2019: Pre-ozonation (target dose of 1.0 mg/L as O3)

• October 14–November 7, 2019: Pre-chlorination (target dose of 0.3 as Cl2)

• November 18, 2019–January 21, 2020: Pre-chlorination (target dose of 1.0 as Cl2) • January 21–27, 2020: Pre-ozonation before particle counter shifted upstream on January 27 (target dose of 0.5 mg/L to 1.0 mg/L as O3)

• May 12–27, 2020: Pre-ozonation (target dose of 0.4 mg/L to 0.55 mg/L as O3)

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Figure 3-5. Particle counts on Floc/Sed 1000 inlet

Vertical lines mark when the pre-oxidation condition varied (raw water with no oxidant[raw], chlorine[Cl2], or ozone[O3]). The shaded box indicates period of time when the particle counter inlet line was moved to the raw water hose bib.

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The particle counters were unreliable during the first month of operations from July 1 to July 31, 2019; therefore, these data were excluded from the dataset. The particle counter calibration, when installed, was not set up correctly and had to be resolved through troubleshooting over the course of the first month of operations. In addition, when a particular bin value was repeated several times, it was presumed to be instrument error and was removed from analysis. This was infrequent and resulted in a small amount of removed data. There were no data when the pilot module was shut down for the filter media change out from February 3 to 18, 2020. In addition, particle counts measured during the turbidity spiking study from June 3 to 13, 2020, were excluded, as those do not represent true raw water, and are presented in Section 5.7.

Generally, particle counts fluctuated either as a result of seasonal variation in algal densities, or from the impact of pre-oxidation, primarily from ozone. Algal densities measured at the intake from February through April correlate to fluctuations in the particle counts, as shown in Figure 3-6. In addition, particle counts, when pre-ozonation was applied, were noticeably lower than when pre-chorine was applied when compared to raw water particle counts (Figure 3-5).

For the month of August, the total particle counts in the raw water averaged 2,501 particles/mL prior to the start of switching to pre-ozonation on Train 1. There were distinctly lower particle counts from August 20 to 30 when pre-ozonation on Train 1 was initiated with a dose of 0.5 mg/L (Figure 3-5). The total particle counts increased consistently after August 30, when ozone was no longer applied; the increase was almost entirely in the 2 to 3 µm bin. Particle counts steadily increased from about September 10 to a high around September 20, after which counts decreased again while pre-chlorination was applied. The increase in particle counts in mid-September corresponds to when an increase in algae counts from about 600 units/mL to 1,200 units/mL in the intake were measured (Figure 3-7). The reduction in particle counts in early October is likely a result of pre-ozonation at a dose of 1.0 mg/L as O3 as the timing of the reduction coincides with the start of the pre-ozone trial. Ozone was stopped and switched to a pre-chlorination condition at a dose of 0.3 mg/L as Cl2, and at this time, the total particle counts increased again back to levels similar to before ozone was dosed. This observation suggests there was a correlation in the change to particle counts and the ozone treatment, but not the chlorination treatment.

Through November and December, particle counts trended generally with raw water turbidity with a clear increase during the start of January, followed by a gradual decrease (Figure 3-5). A consistent short-duration increase occurred around January 24 to 26, which also trended with the turbidity. On January 27, the particle counter sample feed was shifted to a hose upstream of the ozone module to remove potential influence of oxidation. From February 3 to 24, the pilot was offline for the media changeout.

Influent particle counts from February 24 to March 7 were consistent, with total counts on average around 3,500 particles/mL representing raw water characteristics (Figure 3-5). Between March 7 and March 20, particle counts in all bin sizes increased gradually to an average total peak of around 7,000 particles/mL, followed by a gradual decrease again to around 5,000 particles/mL. This increase is consistent with an increase in algal density at the

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intake from 600 units/mL up to 1,600 units/mL at the peak, followed by a decrease to an average algal density of 1,100 units/mL (Figure 3-6). The large peak in algal density is directly related to an increase in the genera Rhodomonas (Komma). The cell size of a typical marine- based Rhodomonas is 10–50 µm, which could explain the notable jump of particle counts in the 5–15 µm range above the other size ranges in mid-March.

Figure 3-6. Influent particle count distribution for raw water (left axis) and algal density at the intake (right axis) February 24, 2020 - April 28, 2020

In April, particle counts and algal densities were fairly consistent throughout the month averaging around 4,300 particles/mL and 1,000 units/mL, respectively, with an exception on April 18 when there was a short duration peak in particle counts up to 7,000 particles/mL.

From April 30 to May 12, when Train 1 was operating in an intermediate ozonation configuration (with no impact on raw water from ozonation), the total particle counts were consistent with an average of 3,305 particles/mL and down from the previous two months when the average monthly particle counts were around 4,300 particles/mL (Figure 3-5). The general decrease in particle counts, compared to the previous month, aligns with a general decrease in total algae counts. Impact of ozonation on particle counts Starting on May 12, there was a distinct step change downward in the particle counts for all bin sizes corresponding to when Train 1 (Floc/Sed 1000) was switched from intermediate ozonation to pre-ozonation. This change in particle counts with ozonation is consistent with past periods from August 20–30, 2020, September 29–October 11, 2019, and January 21–27, 2020, when Train 1 was operating with pre-ozonation (Figure 3-5). In May, ozonation resulted in counts in both the 3 to 5 µm range and 5 to 15 µm range below 500 particles/mL, which is the minimum count needed to be considered viable for the log removal calculation to demonstrate a 2.0 and 2.5-log removal, respectively. As a result, log removals were not presented during the filtration rate comparison period from May 12 through May 26, while both trains operated with pre- ozonation, and therefore, the alternate criteria (<50 particles/mL in filter effluent) was used to demonstrate removal efficacy (see Section 7.3.9.2).

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3.5 Algae

Algae samples were collected weekly at the Headworks intake, which serves as the raw water source to the pilot plant. The water quality is not expected to change from the Headworks intake to the pilot, therefore the results sampled at the Headworks are presented as representative of the pilot raw water quality. Results for algal density in units/mL in the pilot raw water are presented in Figure 3-7 from July 1, 2019, to June 20, 2020. Algal densities ranged from a low of 300 units/mL to a high of 1,600 units/mL during the pilot study duration. The algae enumeration and speciation data identified in this section is based on PWB’s unique sampling and testing program, which uses different analytical approaches as compared to other literature sources. As a result, the algae values reported by PWB may differ in magnitude, and may result in greater values compared to results reported based on other analytical approaches found in the literature. Refer to Chapter 3 of the PDR for more background on historical algae levels in the Bull Run Reservoir (BC 2020).

In general, there were two distinct seasonal fluctuations in total algal density: (1) in late summer starting in mid-August, and (2) again in early March, which are typical for temperate lakes and are observed every year in the Bull Run reservoir. These increases in algal levels were primarily driven by increases in the genera Rhodomonas (Komma) in August and March, and Melosira in late September (Figure 3-8). During the first 4 months of testing, total algal densities ranged from 610 units/mL in mid-July to a high of 1,400 units/mL in late October at the onset of the fall season. There were two samples that were above the PWB threshold for phytoplankton (1,200 units/mL) during the fall time period, including peak measurements of 1,200 units/mL on September 16 and 1,400 units/mL on October 21. Algal density stayed above 800 units/mL until levels gradually decreased in mid-November. Algal density stayed between 300 and 600 units/mL through late February. Levels rose again to above the PWB alert threshold at the start of March with a peak measurement of 1,600 units/mL on March 18. Algal density stayed above 1,000 units/mL until levels gradually decreased again by mid-May to between 600 to 900 units/mL.

Figure 3-7. Total algal density in the raw water intake

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Algae is categorized into major groups based on similar characteristics. Four major groups include cyanobacteria, cryptophytes, and chloroplasts (i.e., green algae), as well as diatoms, each with distinct physical traits. Algae from all the main groups were observed at the Headworks. Within each group, algae are categorized by genera. During the study period, there were 56 unique algae genera detected in the Bull Run reservoir at the Headworks. Typically, algae impacts to drinking water are an issue at higher concentrations. To understand which algae genera are present in the Bull Run reservoir at high concentrations and therefore more likely to lead to treatment issues, the data were sorted by the maximum algal density recorded for each genera, to identify the five algae genera with the highest sample density measured during the pilot duration. Figure 3-8 presents the five algae genera with the highest sample density measured during the pilot testing duration.

Figure 3-8. Algal density for the five genera with the maximum densities sampled

Throughout the pilot study, there were no reported issues with filter operation directly correlated to algae in the intake. For the five algae genera, typically algal densities were below 500 units/mL. Rhodomonas had the highest levels, peaking at 940 units/mL in March. Rhodomonas, which was present at a high density in March, has been observed in PWB’s reservoir before, and is not a known filter clogger or known to cause taste and odor (T&O) issues. Melosira also had one sample above 500 units/mL in October. Of the top five, Melosira and Dinobryon are the only known filter cloggers. The average densities observed for Melosira and Dinobryon were averaging 137 and 66 units/mL, respectively. Additionally, Chlorella, Melosira and Dinobryon can cause T&O issues. During the testing period, there were a few cyanobacterial genera (Aphanocapsa, Aphanothece, Chroococcus and Coelosphaerium) with maximum densities between 55 and 77 units/mL, but none are known cyanotoxin producers.

While algal densities were measured, cyanotoxins were not sampled for during the pilot study at Headworks. Concentrations of cyanobacterial genera did not indicate the presence of blooms in the reservoir.

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3.6 Organics

The full time series display of TOC and DOC is presented below in Figure 3-9 and Figure 3-10, respectively. TOC and DOC were similar throughout the duration, with most of the TOC present as DOC. Monthly average TOC and DOC were approximately 0.75 mg/L at the start of the study. Both TOC and DOC increased to a monthly average over 1 mg/L in October. This increase is typical of seasonal variation and was likely a result of more organic material present in the raw water with fall leaf debris. TOC and DOC decreased to below 1 mg/L beginning in February and remained at a monthly average of approximately 0.8 to 0.9 mg/L through May. The last month of observations yielded organics values higher than previous months at 0.97 mg/L. TOC and DOC average levels were consistent with the historical average levels in the Bull Run reservoir (1.1 mg/L and 2.6 mg/L, respectively) and follow the typical seasonal variation (BC 2020). The maximum observed levels in the pilot intake were all below the historical 90th percentiles (1.6 mg/L and 4.3 mg/L, respectively).

Similar to TOC and DOC, filtered UV254 increased throughout the fall season (Figure 3-11). UV254 is a good surrogate for organic levels in the water source. Additionally, UV254 is a helpful measure for process monitoring as it’s measured using a bench-top instrument, unlike TOC/DOC results that lag by a few weeks for lab analysis. The monthly average UV254 was 0.029 cm-1 in July and increased through the fall to an average of 0.052 cm-1 by November. UV254 remained relatively high throughout the winter and decreased in spring. June yielded a -1 filtered UV254 average of 0.044 cm . UV254 levels observed in the pilot intake were slightly lower than average historical UV254, with the maximum observed levels in the pilot intake below the historical 90th percentile (0.07 cm-1). Overall organic levels reflect an average year for the reservoir.

Figure 3-9. Raw water TOC levels

Figure 3-10. Raw water DOC levels

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Figure 3-11. Raw water filtered UV254 levels

3.7 Metals and Inorganics

Iron and manganese levels measured at the pilot intake through the study duration are presented in Figure 3-12 and Figure 3-13, respectively, with the exception of manganese, which includes data collected at the Headworks for July and August. The water quality is not expected to change from the Headworks intake to the pilot, therefore the results sampled at the Headworks are presented as representative of the pilot raw water quality in the absence of manganese data from the pilot intake during the first two months. Both increased throughout the fall and began decreasing in December, followed by a small increase in May and June. Total iron levels ranged from 16.3 to 118 µg/L with an average of 45.7 µg/L, and total manganese levels ranged from 1.38 to 13.7 µg/L with an average of 5.7 µg/L. Both were well below the secondary MCL of 300 µg/L for iron and 50 µg/L for manganese. The total iron and manganese levels observed during the pilot were well within the range observed historically from the past 10 years, with the maximum observed levels below the historical 90th percentile (130.0 µg/L and 28.4 µg/L, respectively). Seasonal variation of iron and manganese levels reflect similar trends in historical data, as a result of reservoir turnover (BC 2020).

Aluminum was monitored to understand the baseline levels of aluminum at the intake compared to the secondary MCL (200 µg/L) (Figure 3-14). Total aluminum levels ranged from 9.7 to 78.2 µg/L with an average of 24.2 µg/L. The average aluminum level was well below the MCL, and below the historical average (29.2 µg/L) observed at the intake (BC 2020). Additionally, the maximum aluminum level observed is below the historic maximum (132.0 µg/L).

These raw water quality data represent water sent to the pilot module, which can come from different intake depths in the Reservoir depending on the time of year. PWB switches between intake depths to optimize water quality including, but not limited to, water temperature and DO concentrations for instream flows for fish in the Bull Run River, metals, inorganics, and algal concentrations.

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Figure 3-12. Raw water iron concentrations

Figure 3-13. Raw water manganese concentrations

Figure 3-14. Raw water aluminum concentrations

3.8 Summary

General trends in PWB’s raw water at the intake during the pilot study are summarized as follows: • Raw water recorded during the pilot study is representative of historical raw water from the past 10 years in the Bull Run watershed (BC 2020). Overall the raw water quality represents an average year compared to historical data, with the maximum levels for most parameters below the 90th or 95th percentile of the historical dataset. • Water temperature fluctuated seasonally, with the maximum monthly water temperature in September at an average of 16.1°C and the minimum monthly water temperature in January at an average of 5.5°C.

• Alkalinity varied seasonally from fall to winter between 7 and 13 mg/L CaCO3, as expected, changing with the seasonal change in temperature and water chemistry in the Bull Run reservoir. • pH was stable throughout the study period with an average between 7.0 to 7.6.

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• The monthly average turbidity during the study period was between 0.3 and 0.5 NTU, with a full operational range of 0.2 to 1.3 NTU. Grab samples and turbidity observations at Headworks were correlated with each other. While there were occasional increases in turbidity, no natural turbidity events occurred. • Raw water particle counts, which included particle counts not impacted by pre-ozonation, were generally low during the study period in the intake with the exception of two distinct time periods (September 2019 and March 2020) when particle counts increased, which correlated with the timing of increases in algal density. While the highest monthly average total particle counts ranged from 3,800–3,900 particles/mL in September and October and 4,300 particles/mL in March, the average counts in the size ranges serving as surrogates for pathogens were relatively low. Monthly average particle counts in the 3 to 5 µm size range were between 556 to 1,222 particles/mL during the reporting period, indicating that the raw water has a low number of particles similar in size to Cryptosporidium. Particle counts in the 5 to 15 µm range, which is the size of Giardia, were also low with monthly averages between 300 and 1,204 particles/mL; therefore making it difficult to demonstrate log reductions. • In general there were two distinct seasonal fluctuations in total algae density when levels increased in late summer starting in mid-August, and again in early March. These increased raw water algal levels were primarily driven by increases in the genera Rhodomonas (Komma) in August and March, and Melosira in late September. Of the five phytoplankton with maximum densities measured during the testing period, Melosira and Dinobryon were the only known filter cloggers, with average densities observed between 137 and 66 units/mL, respectively. • TOC and DOC at the raw water intake increased as expected in the fall during periods of reservoir turnover, with a peak monthly average TOC of 1.3 mg/L in November. This TOC concentration is low when compared to other surface water in the United States. Additionally, almost all the TOC was present as DOC. • Iron levels ranged from 16.3 to 118 µg/L with an average of 45.7 µg/L, and manganese levels ranged from 1.38 to 13.7 µg/L with an average of 5.7 µg/L. Both were well below the constituent secondary MCL (300 µg/L for iron and 50 µg/L for manganese). The iron and manganese levels observed during the pilot were well within the range observed historically from the past 10 years. Aluminum levels were an order of magnitude below the secondary MCL of 200 µg/L.

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4.0 Approach to Data Analysis and Quality Control

This section describes the processes and procedures used to analyze data generated by the pilot study. Section 4.1 outlines the procedures used for quality control during data analysis, including training, documentation, and instrumentation calibration. Section 4.2 describes data analytics used to characterize pilot performance, much of which focused on filter effluent quality and efficiency. This includes discussion of the analytical parameters used to determine the length of a filter run (i.e., filter run time), which correspondingly defines the UFRV of that filter run. Analytical measures that were used to determine whether or not a filter run was representative of the test conditions are also discussed. Finally, data analytics to determine the organics removal by unit treatment process are presented.

4.1 Data Quality Control

The following sub-sections describe the data quality control procedures that were used for this study.

4.1.1 Training

SOPs that include calibration, operation, troubleshooting, and safety procedures were written for each instrument. The SOPs were available for operators in printed form onsite and archived digitally online at the SharePoint website. As part of initial training, each operator was sent the instruments’ SOP to read, and then signed a “SOP Read” documentation form after completing the required reading. The training documentation was archived both in printed form and digitally online at the project’s SharePoint website. Onsite hands-on training was then performed by a trained operator before approving the trainee’s use of the instrument.

4.1.2 Documentation

Calibrations and verifications were documented in calibration record booklets unique to each instrument or electrode. Calibration standards’ expiration dates were routinely monitored and replaced when necessary. Instrument and electrode factory calibration certificates and calibration standard certificates of analysis, with lot numbers, were archived for audit reference.

4.1.3 Online Instrumentation

The MicroTol+ online turbidimeters were cleaned and their calibration verified with a 1 NTU standard twice per week. If the calibration verification was outside of the acceptable range (0.9–1.1 NTU), the instrument was recalibrated with a two-point calibration (0.02 NTU and

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10 NTU standard). The reporting range for this instrument was typically 0.01–10.00 NTU. During the turbidity spiking period, the reporting range was temporarily changed to 0.01–1,000.0 NTU.

The ThermoScientific Aquasensor data stick pH electrode calibration was verified with a pH 7.00 standard weekly. If the calibration verification was outside the acceptable range (pH 6.9 to pH 7.1), the pH electrode was recalibrated with a two-point calibration (pH 4.01 and pH 10.01) and reverified with the pH 7.00 standard. Data stick pH salt bridges were replaced yearly. Calibration standards were replaced weekly by aliquoting from bulk containers.

Thermometers, pressure gauges including filter head loss sensors, flow meters, particle counters, and ozone probes were not routinely calibrated or verified. Each of these instruments was factory calibrated and remained within the period of validity for this study.

Data from each of the four pilot treatment modules were downloaded on a weekly basis using a remote connection to the modules’ data historians. Following downloading, data were checked for non-representative outliers as described in Section 4.2.1.1.

4.1.4 Water Quality Bench Instruments

The bench instruments were specifically chosen to be able to accurately measure water quality parameters within the necessary minimum reporting limits. The bench instruments were operated in a temperature-controlled room where the humidity was monitored daily to ensure the instruments were operating within their prescribed environmental conditions.

The Hach Intellical PHC281 pH electrode has an open junction that is designed for low ionic strength samples. The pH electrode was calibrated daily before use with a three-point (pH 4.01, pH 7.00, and pH 10.01) standard and verified with a pH 7.38 standard. If the calibration slope (¯60–¯57.5 millivolt [mV]) or the pH verification measurement (pH 7.28–7.48) were outside of the acceptable range, then the calibration was repeated. Calibration standards were replaced weekly by aliquoting from bulk containers.

The Hach TU5200 laboratory laser turbidimeter calibration was verified daily with 10 NTU and a <0.1 NTU standard. If the calibration verification was outside of the acceptable range (9.0– 11.0 NTU), then the instrument was recalibrated with 20 NTU and 600 NTU standard. The low reporting limit for this instrument is 0.001 NTU.

The Hach DR3900 colorimeter was calibrated daily before use for color, ozone, and chlorine analysis when needed. Color was calibrated by using a 15 Platinum Cobalt (Pt-Co) Color Unit standard. The low reporting limit for this analyte is 3 Pt-Co color units. Ozone calibration verification was completed with a three-point verification (0.17 mg/L, 0.43 mg/L, and 0.63 mg/L). The chlorine calibration verification was also completed with a three-point verification (0.22 mg/L, 1.58 mg/L, and 2.73 mg/L).

The RealTech RealUV254 instrument was zeroed daily before use with deionized (DI) water. The low reporting limit for this instrument is 0.001 cm-1.

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The LuminUltra luminometer, used for both aqueous and media ATP, was calibrated daily before use with UltraCheck 1 standard. A duplicate analysis was performed with each batch of samples.

Field data collected by bench instruments was transcribed to spreadsheets daily. The data were reviewed monthly for transcription errors and abnormal measurements, then submitted to be recorded in the laboratory information system. After digital recording, it was spot checked a final time for electronic transcription errors before archival.

4.1.5 Portland Water Bureau Lab Analysis

The PWB Water Quality laboratory is accredited by the Oregon Environmental Laboratory Accreditation Program for analysis of aqueous samples for regulatory reporting under the Safe Drinking Water Act. The lab follows approved analytical methods and implements all specified quality control protocols including calibration, initial and ongoing calibration verification, laboratory control samples, blanks, matrix duplicates, and spikes. The method performance and analytical technique were verified in performance testing studies.

TOC and DOC were the same laboratory analytical procedure ran on the Shimadzu TOC-VWP instrument, except for DOC being filtered in the field with a 0.45 µm PES membrane filter. The laboratory instrument is calibrated twice yearly with a verification sample at the start of every analysis batch to verify ongoing instrument calibration. Once per calendar month an Inorganic carbon spike was performed to verify that inorganic carbon was adequately purged prior to converting the organic carbon to carbon dioxide.

The ICP-MS used to run metals samples was calibrated at the start of each new analysis batch and verified with an initial calibration verification second-source calibration standard. Samples are batched in groups of 20 or fewer, which include a method reagent blank and a laboratory fortified blank. Quality control protocols for all samples and standards used internal standard responses to calculate concentrations of target analytes; replicate integrations that incorporate three replicate integrations for every sample and standard, with the average of the three being reported, and integrated correction equations that uses elemental interference equations to estimate and allow for the subtraction of isobaric interferences.

4.1.6 Eurofins Contract Lab Analysis

Contract lab samples were picked up via courier and shipped to the contract labs. Temperature, holding time, and chain-of-custody requirements were observed in the shipment of the samples.

The carboxylic acid analyses included a set of initial calibration standards, a laboratory reagent blank, an initial continuing calibration check low, and a closing continuing calibration check.

The AOC analyses included one blank, one 0 parts per billion (ppb), and 100 ppb sample per batch of less than 12 samples. Controls were prepared and inoculated separately. Negative controls should show little or no luminescence increase over time. Positive controls should show luminescence growth curve. Positive control results must be higher than negative control

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results. If positive control results were lower than the negative results, then the entire sample set was rerun. Blank control results must be less than 10 µg AOC/L.

4.2 Data Analytics There are multiple ways by which to characterize the performance of a treatment process. In general, treatment efficacy is assessed by characterizing removal of constituents (e.g., turbidity, particles, dissolved organics, etc.). Removal may be characterized either by the percent of the constituent in the raw water that is removed or by the absolute level of the constituent in the treated water. Percent removal is of most interest when assessing individual treatment processes, while absolute levels are of most interest when assessing the performance of the overall treatment train. The pilot simulated full-scale treatment through filtration (i.e., neither disinfection nor corrosion control were assessed at pilot-scale). However, SDS testing was conducted at bench-scale using pilot filter effluent seasonally. The parameters that were of most interest when assessing treatment performance included turbidity, particle counts, and concentration of organics in the filtered water. In addition to treatment efficacy, treatment efficiency was an important metric that was characterized as part of this pilot. The efficiency of the overall treatment train was primarily assessed using the UFRV metric, which measures the productivity of each filter run and is associated with filter run time and filtration rate. Filter run time was used as a secondary metric, recognizing that a filter operated at higher filtration rates may still require backwashing more frequently and this is an important operations consideration.

Many of the parameters used for the treatment performance assessment were collected using online instrumentation, which recorded data every 5 minutes while the treatment processes were operational. The resultant data set was trimmed to exclude data outside of the calculated filter runs, as described in the following section.

4.2.1 Filter Run Time and UFRVs

Filter productivity is assessed using the UFRV metric, which normalizes filter run time with filtration rate to assess the volume of water treated per unit filter area for a given filter run. UFRV is calculated by multiplying the filtration rate (in gpm/sf) by the filter run time (in minutes). Because UFRV normalizes the filter run time by the filtration rate, it can be used to compare performance between filters operated at different filtration rates. Filtration rate generally remained constant between multiple filter runs and over the pilot operation. Section 2.3 describes the filtration rates throughout the pilot study.

Because filtration rate was set as an independent variable, filter run time was the only dependent variable assessed as part of the UFRV calculations. As such, filter run time varied between runs in response to other independent variables, such as raw water quality, pre- oxidant, coagulation/flocculation/sedimentation, and filter aid conditions.

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For the purpose of this study, a distinction is made between calculated filter run time, based on the period of time during which filter effluent turbidity and head loss met the target filter goals, and physical filter run time, which is the time between filter backwash events. Depending on the filter effluent turbidity and/or head loss, calculated filter run time may match the physical filter run time or be less than the physical filter run time. However, it is not possible for the calculated filter run time to exceed the physical filter run time. The physical filter run time ended when the filters backwashed, which in turn was triggered when one of the following criteria were met: • Filter effluent turbidity exceeded trigger level of 0.15 NTU for more than 1 minute (trigger level of 0.20 NTU was used during startup and commissioning) • Total head loss through the filter exceeded 12 ft • Total filter run time exceeded 100 hours (this criterion was not triggered during the course of this pilot study)

The calculated filter run time was determined algorithmically, based on a lower filter effluent turbidity level and/or a lower total head loss threshold. Any threshold lower than the thresholds used to physically backwash a filter could be selected, but for the purposes of this report the filter effluent turbidity threshold used to calculate the end of a filter run was 0.10 NTU. For much of the study period, the physical backwash threshold of 12 feet was used to determine the end of calculated filter runs. Based on feedback from the design team, select filter runs have also been analyzed using a total head loss threshold of 10 feet to determine the end of the calculated filter run. Runs that have been calculated using this lower head loss threshold will be clearly identified as such; otherwise, the physical backwash threshold of 12 feet of total head loss was used to determine the end of the calculated filter run.

The algorithm used to calculate filter run time performs two functions: • It removes the portion of the ripening curve during which filter effluent turbidity is above 0.10 NTU from the beginning of the filter run, and • It calculates the end of the filter run as occurring when either of the thresholds were exceeded: − More than 5 percent of the filter effluent turbidity values recorded were above 0.10 NTU (but less than 0.15 NTU), or − The total filter head loss exceeds the terminal head loss threshold of 12 feet.

The first criterion excludes data that were collected during the ripening period, which, in the full-scale facility, would correspond with a filter-to-waste operation. There is no equivalent criterion for removing data from the start of a filter run based on total head loss.

The second criterion evaluates the filter run against the two thresholds used to determine the end of a calculated filter run. The filter effluent turbidity threshold is based on the PSW goal of maintaining 95 percent of filter effluent turbidity values at or below 0.10 NTU. An example of how this works in practice is presented graphically for a typical filter run in Figure 4-1.

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Figure 4-1. Example of data used to calculate filter run time

The head loss threshold is a stricter criterion, and ends the filter run as soon as the head loss exceeds the threshold. If evaluating filter runs against a total head loss threshold of 10 feet, the calculated run will end as soon as the total head loss exceeds that threshold. When evaluating filter runs against a total head loss threshold of 12 feet, the run will similarly end as soon as the total head loss exceeds that threshold; because 12 feet was the head loss threshold used to determine when a filter physically needed to be backwashed, it was not possible for the pilot filters to develop head loss in excess of 12 feet.

At times, operations were such that the filter effluent turbidity for an entire run was below the 0.15 NTU threshold for physically backwashing the filter, but above the 0.10 NTU threshold for ending a calculated filter run. Such runs, which occurred infrequently, were typically the result of either pretreatment challenges (e.g., loss of filter aid) or instrumentation errors with the turbidimeter. As a consequence of these operational issues, the data from those runs were removed from the final data set of accepted filter runs used for statistical summaries. There are instances where these data are presented to demonstrate the value of a particular operational scheme, such as Section 5.1.2.5 where filter aid is discussed. If there was not an operational issue, the data were retained in the statistical summaries.

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4.2.1.1 Filter Run Data Review and Quality Assurance/Quality Control

Each calculated filter run that was defined as described in the preceding section was assessed to verify the pilot operations were representative of the test condition being evaluated. To assess whether or not data from each filter run were representative, each run was graphically assessed using time series plots showing the filter’s head loss, effluent turbidity, and effluent particle counts over the duration of the run. Filter run plots from each filter were generated on a weekly basis, with calculated run start and end times determined algorithmically as described above. Each run was reviewed visually for abnormalities in the shapes and/or slopes of the head loss, effluent turbidity, and effluent particle count curves. Additionally, the head loss and effluent turbidity at the time the filter physically backwashed were reviewed to identify abnormalities; filter runs that ended before reaching the terminal head loss and/or turbidity limits used for backwashing (12 feet and 0.15 NTU, respectively) were subjected to additional scrutiny to assess the reason for backwashing. If any irregularities were noted for any of the filter runs, the operating logs were reviewed to determine if operational issues had occurred during the run that would have resulted in non-representative data.

For example, if chemical feeds were not consistent because of operational issues (e.g., air-lock of a chemical feed pump for a filter), data collected from filters affected by the operational issue were removed from the final data set used for analysis. When removed, the reason for removal was noted. Operational issues, manually-initiated backwashes, and power failures were all common reasons for removing filter runs and censoring the associated data.

4.2.2 Turbidity

As described above, filter effluent turbidity is one of the criteria used to determine the start and end time for each filter run for UFRV processing. In turn, the start and end times for each filter run were used to truncate the filter effluent turbidity data set so that only filter effluent turbidity data from accepted filter runs were used to characterize filter effluent quality. This step was necessary to limit the data used for analysis to those representing water that would be distributed at a full-scale treatment facility. Data collected prior to the calculated filter run start time correspond to water that would be sent to filter-to-waste at full-scale, and full-scale filters would be backwashed at the filter run end time rather than allowing the filter’s effluent turbidity to continue to increase. Data visualizations and summary statistics shown in the following sections will include only filter effluent turbidity data recorded between the start and end times of accepted filter runs.

On rare occasions, the filter effluent turbidimeters measured incorrect turbidity readings due to instrumentation error (e.g., vial fogging, communication faults, etc.). If the erroneous filter effluent turbidity readings prematurely ended a filter run (i.e., the filter shut down before any of the three triggers listed above were reached), the associated run was considered non- representative (because the UFRV and run time would be shorter than would be indicated by actual filter effluent turbidity or head loss data). Runs that were considered to be non- representative were removed from the final data set of accepted filter runs.

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4.2.3 Head loss

As stated in Section 4.2.1, this study used two terminal head loss criteria when evaluating the length of a filter run. For the majority of the study, the terminal head loss criterion used was 12 feet, which corresponds to the terminal head loss threshold used to determine when a filter physically needed to be backwashed. For some filter runs, a lower threshold of 10 feet was selected to determine if the treatment goals could still be met if less head was available for the design. See 7.3.9.5 for a discussion of when the lower head loss threshold of 10 feet was used as the terminal head loss criterion to determine the end of calculated filter runs. No other head loss thresholds have been evaluated in the course of this study.

In practice, if the filter run previously terminated due to head loss, changing the total head loss threshold lowered the filter run by a certain percentage. If the filter run terminated due to turbidity, it is possible that it may have instead terminated due to head loss if the terminal head loss criteria were changed. Some filter runs that terminated due to turbidity would still terminate due to turbidity after the change, if the accumulated head loss was less than 10 feet when the turbidity criterion was exceeded.

The algorithms used to calculate filter run time and UFRVs do not explicitly consider CBHL; however, this parameter inherently influenced filter run time because it is the other bound (besides the terminal head loss threshold) that sets the range over which head loss can accumulate. For the purposes of this study, the second head loss value recorded after a backwash is considered to represent the CBHL for that run; because data were recorded at 5-minute intervals, this value represents the head loss that occurs between 5 to 10 minutes into a filter run. The Interim Pilot Study Report used the first head loss value recorded after backwashing to represent CBHL, but it was found that there was considerable variation in CBHL values that were thought to be associated with instrumentation limitations. Specifically, the instruments recording the hydraulic head take a few minutes to stabilize after startup. Using the second head loss value (i.e., 5 minutes after startup of a filter run) eliminated much of this variation, and provides a more consistent assessment of trends in CBHL over time.

4.2.4 Particle Counts

In addition to the particle counters on each filter, particle counters measure particle counts in the influent and settled water streams to Floc/Sed 1000 on Train 1. These particle count data, along with the filter effluent particle count data, were removed if they did not meet the following criteria at the time of collection: • Measurement cell transmittance ≥ 90 percent. During unique circumstances, data were accepted when measurement cell transmittance ≥ 85 percent when no other data were available • Sample flow rate within the flow ranges specified below: − Flow to filter particle counters between 60 mL/min to 90 mL/min − Flow to Floc/Sed 1000 particle counters between 50 mL/min to 80 mL/min

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Particle counts were binned into nine discrete particle size ranges over the course of the filter run. For the purposes of this report, the following size ranges will be presented for discussion: • 3 to 5 µm (surrogate for Cryptosporidium) • 5 to 15 µm (surrogate for Giardia) • 2 to 100 µm (total particles)

As with other filter data, the particle count data have been truncated based on calculated filter run time. Particle count data collected during runs that were not considered to be representative, as described in Sections 4.2.1 and 4.2.2, were removed from the particle count data set.

Log removal values for particle counts were computed by pairing filter effluent particle counts to raw water particle counts for the same aliquot of water, computed based on the system’s hydraulic residence time (HRT) between the raw and filter effluent sample locations 1. Data pairs were only retained for analysis when the raw water particle counts were greater than 500 particles/mL to ensure that it is mathematically possible to demonstrate a 2.5-log removal without excluding an excessive amount of particle count data. Similarly, any reported values where the reported particle count was zero for the 3 to 5 µm and 5 to 15 µm ranges were transformed to a value of one (1) particle/mL to ensure that a log removal computation did not produce an infinite result. Records where the total particle counts were zero were considered to represent an instrument error, and were not included in the data set.

As a Bin 1 system, PWB would be required to achieve 2-log removal of Cryptosporidium and 2.5-log removal of Giardia. For pilot testing, particles in the 3 to 5 µm bin are considered a surrogate for Cryptosporidium, while those in the 5 to 15 µm bin are a surrogate for Giardia. However, because the Bull Run source is naturally low in particles, it is difficult to demonstrate removal of particles at that level strictly because there are insufficient particles in the raw water. Therefore, the approved Work Plan established an alternate criterion, which limits particles in the 5 to 15 µm bin to ≤50 particles/mL for at least 95 percent of the measurements during an individual filter run (see Section 1.4 for the water treatment goals).

This criterion was established based on the aggregate data set. Therefore, the data presented in the particle count tables in this report represent the specified percentile from all of the representative filter runs conducted during the test condition. For example, the 95th percentile represents the 95th percentile of the aggregated data set.

1 The particle counts used for this calculation were typically recorded from the inlet to Floc/Sec 1000, which was typically representative of raw water. At times the water was pre-oxidated with ozone, which appeared to have lowered the particle counts compared to those in untreated raw water.

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Because of the difficulty in proving treatment effectiveness when raw water particle counts are low, the particle count tables in this report only present average log removals from paired data (based on HRT between raw water particle count and filter effluent particle count sample locations) when then raw water exceeds 500 particles/mL. This criterion is still quite stringent, considering that a raw water particle count of 500 particles/mL requires a filter effluent particle count ≤5 particles/mL to demonstrate 2-log removal. Therefore, statistics on the actual particle counts in the relevant size ranges (3 to 5 µm and 5 to 15 µm) are presented in the tables alongside the calculated log removal. If there were insufficient raw water particles in the relevant size ranges, log removals are presented as “--”.

4.2.5 Organics Removal

Organics removal through the treatment process was assessed for the testing scenarios in terms of TOC, UV254, and color. Apparent color for raw water is presented from July 1–23 in the absence of true color data. Apparent color is unfiltered and may have interference from turbidity that appears as color for the raw water. Color data that were below the detection limit (3 Pt-Co units) were replaced with half the detection limit (1.5 Pt-Co units) for reporting purposes.

4.3 Data Presentation

This report presents data in a number of formats, including tables, time series plots, and box and whisker plots. The following paragraphs describe the box and whisker plot format used in this report, because there are several variations of box and whisker plots that can be used for data presentation and analysis.

The box and whisker plot format is used in this report to primarily to summarize filter performance parameters including UFRV, filter run time, and turbidity. The x-axis labels typically will include the filter number, media type, and depth, along with the filtration rate in gpm/sf. Above the x-axis, the number of runs or samples included in the analysis for each filter are presented. A horizontal dotted line may be added to represent the performance goal; for example, box plots of UFRV data will including a horizontal dotted line representing the minimum UFRV goal of 6,500 gallons per square foot per filter run (gal/sf-run) for 95 percent of the operation, as specified in Table 1-1 and the Work Plan (BC 2019). The 6,500 UFRV is based on a desired full scale facility production of 145 mgd. UFRV plots also include a horizontal dashed line that represents a higher desired UFRV performance goal of 10,000 gal/sf-run (Table 1-1).

For box and whisker plots, the bottom of the box represents the 25th percentile value or first quartile where 25 percent of the data are below this value. The top of the box represents the 75th percentile value or third quartile where 75 percent of the data are below this value. The line in the middle of the box is the median or 50th percentile value. The difference between the first and third quartiles is defined as the interquartile range (IQR).

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The lines that extend from the box, known as whiskers, represent either the maximum or minimum value recorded, or 1.5 times the IQR if outliers are suspected. Values that are more than 1.5 times the IQR above third quartile or more than 1.5 times the IQR below the first quartile are suspected outliers. For example, if the maximum recorded value was less than 1.5 times the IQR, the upper whisker would extend to that maximum value. If the maximum value recorded exceeded 1.5 times the IQR, the upper whisker would extend to 1.5 times the IQR above the upper hinge.

Similar logic extends to the representation of the lower whisker. For clarity, data outside 1.5 times the IQR have not been plotted in the box plots presented in this report, but those data have been included when calculating summary statistics such as percentiles. The black triangles on the plots represent the 95th percentile where 95 percent of the data are below this value. The black triangle often aligns with the performance goals specified in Table 1-1.

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5.0 Coagulation, Flocculation, and Sedimentation

This section describes the evaluation of the coagulation, flocculation, and sedimentation processes, and observations of key operating parameters for each.

5.1 Coagulation Testing and Selection

This section describes the bench-scale jar testing conducted in preparation for the pilot testing to inform the initial coagulant selection (Section 5.1.1), followed by detailed results from the coagulant testing and selection at the pilot (Section 5.1.2). Four primary coagulants (alum, ferric chloride, polyaluminum chloride [PACl], and aluminum chlorohydrate [ACH]) were evaluated during bench- and pilot-scale testing.

The objective of coagulant testing at bench-scale was to evaluate the effectiveness of each coagulant in reducing turbidity, organics, and color to determine if any coagulants could be eliminated from consideration at pilot-scale. The objective of pilot-scale coagulant testing was to establish a consistent pretreatment approach that was used in subsequent testing of other important treatment parameters. It was not the intent of the bench- or pilot-scale coagulant testing to dictate what specific coagulant or coagulant aid chemicals the full-scale facility will use.

5.1.1 Bench-scale Jar Testing

Prior to startup of the pilot plant testing, PWB, BC, and Confluence Engineering staff conducted jar testing to evaluate coagulants and coagulant aids. The bench testing approach was based upon conducting a multi-phased group of jar test runs. Testing evaluated coagulation performance with Bull Run water across three phases of tests by (1) performing a wide-range dose screening of coagulants, (2) evaluating narrowed coagulant dosage ranges that performed the best, and (3) evaluating coagulation assisted by cationic, nonionic, and/or anionic polymer(s). More detailed results for each jar testing round are included in Appendix D.

PWB conducted jar testing in the PWB Interstate Lab with inorganic, metal-salt coagulants, and some select polymer blends, including the following: • Alum (Kemira Chemicals, Inc.) • Ferric chloride (PIX-311, Kemira Chemicals, Inc.) • PACl (PAX-18, Kemira Chemicals, Inc.) • ACH (PAX XL-19, Kemira Chemicals, Inc.) • Clarifloc C-3226 (filter aid cationic polymer, polyacrylamide, Polydyne Inc.) • Praestol 851TR (coagulant aid cationic polymer, polyacrylamide, Polydyne Inc.)

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• Praestol 650TR (coagulant aid cationic polymer, polyacrylamide, Polydyne Inc.) • Praestol 3040LTR (filter aid anionic polymer, polyacrylamide, Polydyne Inc.) • Praestol 2500 (filter aid nonionic polymer, polyacrylamide, Polydyne Inc.)

In practice, the addition of metal ion coagulants will decrease pH and alkalinity. The extent of this decrease depends on the coagulant being used, with alum and ferric having more of an impact than PACl and ACH. To counter-act these effects, alkalinity (in the form of sodium bicarbonate [NaHCO3] was added, when necessary, to increase the buffering capacity of the coagulated water and limit the reduction in pH.

PWB conducted jar testing on water collected in December 2018, March 2019, and April 2019, as summarized in Table 5-1. The December 2018 water captured raw water with higher than typical organics for the source water. March water quality samples were comparable to historical seasonal averages. The April test water had an increased turbidity and was collected from a tributary feeding the Bull Run reservoirs following a storm event. To simulate reservoir water, the April test water was pre-settled prior to jar testing, resulting in a reduction of turbidity from 2 NTU at the time of collection to 0.84 NTU.

Table 5-1. Raw Water Quality Summary for Bench-scale Jar Testing

Testing Month and Year Turbidity (NTU) Alkalinity (mg/L as CaCO3) TOC (mg/L) December 2018 0.35 9.5 1.5 March 2019 0.26 7.8 1.0 April 2019 0.84 5.4 2.0

Testing on water processed by jar testing included evaluation of the filterability index (FI) on settled water. The FI test is a method to compare coagulant types and dosages against each other for their later potential to be filtered. The FI test involved recording the time it took to filter a standard volume of water and measuring turbidity in the filtered water. The jar test analysis included evaluations of visual floc appearance and time of initial formation and analysis of settled water for pH, turbidity, apparent color, true color, alkalinity, UV254 (unfiltered and filtered through a 0.45 µm filter), TOC, and DOC. Visible floc was difficult to obtain in jar testing. Results showed that low coagulant doses had positive results when considering filterability, decreasing turbidity, and removing organic matter.

After the completion of the first round of testing (December 2018), observations included: • Very low raw water turbidity represents a challenge to traditional jar testing when relying on visual indications of floc formation and settling. • Most coagulants showed good particle removal at both low and high coagulant dosages, with some coagulants showing excellent TOC and DOC removals at the higher dosages. Significant (>30 percent) TOC reduction was observed at low coagulant dosages thought to be at charge neutral, but without instruments to measure the charge of the water, the optimal low dosages were not consistently identified.

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• The addition of coagulant aid showed mixed results with the different coagulants. In combination with ACH, lower turbidity and better filterability were obtained but this was not the case for alum and ferric. PACl was not evaluated in combination with coagulant aid.

During the second round of testing (March 2019), the following results were observed: • All primary coagulants performed well with respect to filterability and FI turbidity at dosages ranging from 0.26 mg/L as Al3+ through 1.49 mg/L as Al3+ for PACl, alum, or ACH, and dosages ranging from 0.97 mg/L as Fe3+ through 1.61 mg/L as Fe3+ for ferric. • There was significant removal of DOC, at times a 40 to 60 percent reduction, when primary coagulants were dosed at 0.44 to 1.49 mg/L as Al3+ or 1.61 mg/L as Fe3+.

The third round of jar testing (April 2019) continued to show that low coagulant doses had significant potential for pilot testing selection. A summary of findings from the April 2019 jar testing included the following: • All coagulants showed relatively good turbidity and filterability performance at ≤1.79 mg/L as Al3+ or ≤1.94 mg/L as Fe3+ dose (e.g., good performance was observed at 0.26 to 0.89 mg/L as Al3+ or 0.97 mg/L as Fe3+). • Excellent reduction in organics was achieved. TOC results (unfiltered samples) show that settling alone removes at least 20 percent of TOC at a dose as low as 0.26 mg/L as Al3+ for all aluminum-based coagulants, and at a dose as low as 0.97 mg/L as Fe3+. Alum and ferric removed a high level of DOC at doses as low as 0.53 mg/L as Al3+ or 1.94 mg/L as Fe3+, respectively. All coagulants removed >70 percent of DOC at a dose of 0.79 to 1.68 mg/L as Al3+ or 2.91 mg/L as Fe3+.

Jar testing along with a combination of assessments involving the review of specific treatment parameters were completed to determine which coagulants (and coagulant aid) may be useful to evaluate during pilot testing. Based on the assessment of treatment parameters (such as turbidity removal, FI turbidity and filtration time, and reduction in organic matter surrogates including color, UV254, DOC, and TOC), the results from jar testing were not definitive enough to remove any potential coagulants for investigation during pilot operations. Therefore, all four coagulants were evaluated via pilot testing.

5.1.2 Pilot Coagulation Selection–Summer/Fall

After 3 weeks of initial wet testing, operation with chemical addition began in start-stop mode from June 18–30, 2019, with the goal to select chemical dosages to validate during continuous operation. The first week of coagulant testing involved comparing alum and ferric chloride, followed by a week comparing the other two coagulants, PACl and ACH. Data collected during this period were used to inform chemical dosages used during subsequent continuous operation.

Full continuous operation of the pilot commenced on July 1, 2019. The initial screening period during continuous operation evaluated alum and ACH initially for 1 week, followed by a week of testing with PACl and ferric. Then the coagulants were narrowed down to alum and PACl, which were tested for 1.5 months through the end of August. The evaluation looked at how alum and

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PACl performed with the addition of filter aid, coagulant aid, and pre-oxidation with ozonation. The following section discusses the performance of each coagulant during the initial screening, followed by results from the alum and PACl side-by-side comparison testing.

The SCM online instrument and bench-top zeta potential analyzer were installed following the coagulant selection testing. The particle counters initially provided for the pilot were not properly calibrated by the equipment provider. A field calibration of the pilot’s particle counters was conducted by Chemtrac on July 31, 2019. Particle count data collected prior to that date are considered unreliable and are not presented.

During start-up from July 1 to July 26, 2019, the filters were initially operated at filtration rates of 8 gpm/sf for the 72-inch deep filters (Filters 1, 3, 4, and 6) and 6 gpm/sf for the 60-inch deep filters (Filters 2 and 5). On July 26, 2019, the filtration rates on all filters were increased. The filtration rate on the 72-inch deep filters (Filters 1, 3, 4, and 6) was increased from 8 to 12 gpm/sf, while the filtration rate on the 60-inch deep filters (Filters 2 and 5) was increased from 6 to 8 gpm/sf.

5.1.2.1 Alum–Initial Screening The initial alum dose was chosen based on the three rounds of jar testing performed prior to the pilot testing. The initial alum dose during intermittent operations was set at 0.29 mg/L as Al3+ and was adjusted to 0.37 mg/L as Al3+. Alum was dosed at 0.37 mg/L as Al3+ from July 1–5, followed by the addition of 0.03 mg/L nonionic filter aid from July 5–8, 2019. During this period, the filters were operated at 8 gpm/sf for the 72-inch deep filters (Filters 1, 3, 4, and 6) and 6 gpm/sf for the 60-inch deep filters (Filters 2 and 5). During this initial screening of coagulants, relatively few runs were collected because of the manner in which the pilot was initially operated during startup. The filters were originally set to backwash based on a 0.20 NTU turbidity threshold, which allowed for extended filter runs collecting data above the 0.10 NTU target. This is illustrated in Figure 5-1, which compares turbidity and head loss data collected from Filter 6 during the initial screening of alum to the turbidity corresponding to the calculated filter runs (calculated using the procedure outlined in Section 4.2.1).

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Figure 5-1. Comparison of Filter 6 turbidity and head loss data (top) to Filter 6 turbidity and head loss data corresponding to calculated filter run times (bottom) during initial alum screening

UFRVs for the runs conducted during this period are shown on Figure 5-2. Most UFRV plots will be plotted as a box plot, indicating relevant statistics of the UFRV data set for that condition. However, if fewer than three runs were accepted during the evaluation period, as is the case with Figure 5-2, the box plot will be replaced by a point plot that directly indicates the UFRV corresponding to each run.

Figure 5-2. Calculated UFRVs during the initial screening of alum on Train 1, July 1–8, 2019

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Figure 5-3 summarizes the filter effluent turbidities recorded during the runs that are represented in Figure 5-2. Turbidities recorded during periods that were truncated from the filter run record have not been included.

Figure 5-3. Filter effluent turbidities recorded during accepted filter runs during the initial screening of alum on Train 1, July 1–8, 2019

Filter productivity was generally good during this time with coagulant only from July 1 to July 5, 2019, and the addition of filter aid on July 5, with UFRVs greater than 10,000 gal/sf-run. Filter effluent turbidities were generally low on the anthracite filters (Filters 5 and 6) through the bulk of their runs. The GAC filter (Filter 4) had higher filter effluent turbidities than the anthracite filters during this test period, and correspondingly lower filter productivity. Particle count data were not available for this test condition.

Table 5-2 summarizes average TOC and UV254 from July 1 to 8, 2019, when the pilot was operated at filtration rates of 6 and 8 gpm/sf. For TOC reported as less than the method reporting limit (MRL), the value was reported as half the MRL (0.15 mg/L).

During the initial testing from July 1 to 8, while TOC increased in the settled water, organics levels were reduced through filtration for all filters from the raw water. Differences in organics removal between the media types were observed during this testing period. Both anthracite filters removed TOC to approximately 0.5 mg/L (33 percent). UV254 was reduced more with the GAC filter (85 percent for the GAC filter) than in the two anthracite filters (54 and 60 percent for the anthracite filters). Color was reduced from an average of 4.5 Pt-Co in the raw water to below the MRL (3 Pt-Co) following treatment.

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Table 5-2. Average Organics Reduction During the Initial Screening of Alum on Train 1, July 1-8, 2019 TOC Average Removal Sample Location Average TOC Average Percent Removala No. of Samples Std Dev (mg/L) Raw water 0.74 -- 2 0 Settled water 1.17 -58% 2 0.47 F4-GAC-72, 8 gpm/sf 0.15 80% 2 0 F5-Anth-60, 6 gpm/sf 0.48 34% 2 0.04 F6-Anth-72, 8 gpm/sf 0.49 34% 2 0.03

Average Reduction of UV254

Sample Location Avg UV254 Average Percent Reductiona No. of Samples Std Dev (cm-1) Raw water 0.032 -- 4 0.006 Settled water 0.028 12% 4 0.003 F4-GAC-72, 8 gpm/sf 0.005 85% 2 0.001 F5-Anth-60, 6 gpm/sf 0.012 60% 4 0.003 F6-Anth-72, 8 gpm/sf 0.013 54% 4 0.006

a. Average TOC removal and UV254 reduction were determined by averaging the computed daily reduction of TOC and UV254 between raw and individual filter effluent.

5.1.2.2 Ferric Chloride–Initial Screening Ferric chloride was tested during the initial testing period from June 18 to 25, 2019, while in start-stop operation. During the initial testing phase, non-ionic filter aid (Clarifloc N-6310) was necessary to get the filters to come off the FTW cycle. Based on the initial testing, a starting dose of 0.48 mg/L as active iron (Fe3+) was used for the coagulant comparison trial starting on July 9, 2019, in combination with nonionic filter aid (0.01 to 0.05 mg/L). Cationic coagulant aid (Clarifloc C359, polyamine) was added on July 12 at a dose of 1.3 to 1.6 mg/L for the remainder of the trial. Initially, coagulant aid showed improvement in filter operation, but this improvement was not sustained. Throughout the testing period, the following ferric dosages were used: 0.32, 0.40, 0.48, 0.65, 0.89, 1.29, 1.61 and 2.26 mg/L as Fe3+. The ferric dosage that resulted in the highest UFRV was 0.40 mg/L as Fe3+, in combination with coagulant aid and filter aid. As evidenced by the multiple ferric dose adjustments during the initial coagulant screening, it was difficult to produce acceptable water quality using ferric coagulation. Acceptable filter performance was not achieved during the ferric screening, as shown in Figure 5-4.

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Figure 5-4. Turbidity from Filter 3 during the initial ferric coagulant screening

These results are not intended to indicate that ferric cannot be used to effectively treat Bull Run water. Instead, they only indicate that proper conditions for use of ferric were not identified during the initial screening period.

Organics removal across the treatment process when ferric chloride was dosed as the coagulant are summarized in Table 5-3. Removal of organics with ferric was limited compared to performance with the other coagulants tested. Effectively, treatment did not remove TOC from the raw water beyond what was removed in the GAC columns (presumably because the adsorptive capacity of the GAC had not yet been exhausted). This supports the general finding that proper conditions for ferric coagulation were not found, either because the coagulant dose was off or the coagulation pH was above what is optimum for ferric coagulants. The pH was kept above 6.3 in order to meet the discharge requirements.

Table 5-3. TOC Removal During the Initial Ferric Coagulant Screening, July 9–15, 2019 TOC Average Removal Sample Location Average TOC (mg/L) Average Percent Removala No. of Samples Std Dev Raw water 0.74 -- 3 0.01 F1-Anth-72, 8 gpm/sf 0.62 16% 3 0.19 F2-GAC-60, 6 gpm/sf 0.33 55% 3 0.16 F3-GAC-72, 8 gpm/sf 0.34 53% 3 0.17 a. Average TOC removal was determined by averaging the computed daily removal of TOC between raw and individual filter effluent.

Similarly, color was not removed in the filters and UV254 was not reduced. At times, ferric added yellow color that could be visually seen in operation and was also measured, even at low ferric dosages. This is also indicative that the coagulant remained as dissolved iron instead of precipitating as iron hydroxide. For UV254, an average of 5 percent increase was observed in the GAC filters and a 33 percent increase was observed in the anthracite filter. Similarly, an average of 3.5 percent increase in color was observed in the GAC filters and a 17 percent increase in color was observed in the anthracite filter.

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5.1.2.3 PACl–Initial Screening PACl was initially tested during start-stop operation at a dose of 0.77 mg/L as Al3+ based on bench-scale jar testing performed prior to the pilot testing. PACl was tested again from July 9 to 15, 2019, with continuous operation at filtration rates of 6 and 8 gpm/sf. During this initial testing period, PACl was dosed between 0.64 and 0.77 mg/L as Al3+ with non-ionic filter aid (Clarifloc N-6310) dosed between 0.01 to 0.03 mg/L.

With the presence of filter aid and polymer aid, turbidity and head loss are shown in Figure 5-5, with the initial run on July 9 removed from analysis due to a manual backwash on-site.

Figure 5-5. Turbidity and head loss data from Filter 6 during the initial PACl coagulant screening

Similar to the initial alum screening, pilot operations during the initial PACl screening limited the number of filter runs collected. This was compounded by mechanical issues with Filter 4 that limited operations during this period. UFRVs calculated for the filter runs collected during the initial PACl screening are shown in Figure 5-6. UFRVs were high during this testing period with UFRVs surpassing 10,000 gal/sf-run. During this limited testing, the 8 gpm/sf anthracite filter had the highest filter productivity.

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Figure 5-6. Calculated UFRVs during the initial screening of PACl on Train 1, July 9–July 15, 2019 Filters 4 is excluded from the figure due to no acceptable filter runs during this time period.

Filter effluent turbidities recorded during the filter runs shown in Figure 5-5 are summarized in Figure 5-7. Both anthracite filters maintained a median filter effluent turbidity near 0.05 NTU during these runs.

Figure 5-7. Filter effluent turbidities recorded during accepted filter runs during the initial screening of PACl on Train 1, July 9 -July 15, 2019 Filters 4 is excluded from the figure due to no acceptable filter runs during this time period.

Average TOC and UV254 from July 9 to 15, 2019 prior to the filtration rate change, are summarized in Table 5-4. As mentioned above, Filter 4 (GAC at 8 gpm/sf) had mechanical issues that limited operations during this period, therefore no data are presented for that filter. For the initial testing period, the anthracite filters (Filters 5 and 6) removed TOC to 0.41 mg/L and

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0.46 mg/L, respectively (42 percent removal on average). UV254 was also reduced through filtration by an average of 62 percent for both anthracite filters. Color was reduced from an average of 3.5 Pt-Co in the raw water to below the detection limit (3 Pt-Co) in the anthracite filters.

Table 5-4. Average Organics Reduction During the Initial Screening of PACl on Train 1, July 9–July 15, 2019 TOC Average Removal Sampling Location Average TOC (mg/L) Average Percent Removala No. of Samples Std Dev Raw water 0.74 -- 3 0.01 F5-Anth-60, 6 gpm/sf 0.41 45% 3 0.04 F6-Anth-72, 8 gpm/sf 0.46 38% 3 0.04

Average Reduction of UV254 Sampling Location -1 a Average UV254 (cm ) Average Percent Reduction No. of Samples Std Dev Raw water 0.027 -- 4 0.001 F5-Anth-60, 6 gpm/sf 0.009 65% 5 0.003 F6-Anth-72, 8 gpm/sf 0.012 57% 5 0.002

a. Average TOC removal and UV254 reduction were determined by averaging the computed daily reduction of TOC and UV254 between raw and individual filter effluent.

5.1.2.4 ACH–Initial Screening ACH was initially tested during start-stop operation at doses of 0.51 and 0.74 mg/L as Al3+. A dose of 0.51 mg/L as Al3+ resulted in longer filter runs than 0.74 mg/L as Al3+ and was selected for the comparison trial from July 1–8, 2019. Filter aid was added on July 6, at a dose of 0.02 mg/L for the remainder of the testing period.

As with the alum and PACl screening, operations during the initial screening of ACH limited the number of filter runs observed during the test period. However, compared to the alum and PACl tests, the ACH tests were characterized by filter runs with low productivity (UFRVs less than 5,000 gal/sf on the 8 gpm/sf filters [Filters 1 and 3] and less than 10,000 gal/sf on the 6 gpm/sf filter [Filter 2]) followed by extended breakthrough of turbidity, as illustrated below in Figure 5-8. These short runs resulted in more runs occurring during the test period, as reflected in Figure 5-9.

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Figure 5-8. Turbidity and head loss data from Filter 3 during the initial ACH coagulant screening, July 1–8, 2019

Figure 5-9. Calculated UFRVs during the initial screening of ACH on Train 2, July 1–8, 2019

Filter effluent turbidities corresponding to the filter runs shown in Figure 5-9 are summarized Figure 5-10. Overall, filter effluent turbidities were relatively high, with median filter effluent turbidities in all three filters ranging between 0.07 to 0.08 NTU.

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Figure 5-10. Filter effluent turbidities recorded during accepted filter runs during the initial screening of ACH on Train 2, July 1–8, 2019

Organics removal across the treatment process when ACH was tested is summarized below in Table 5-5. The GAC filters reduced TOC from raw water by 70 to 80 percent, compared to the anthracite filter, which removed TOC by about 34 percent. All the filters had excellent reduction of UV254 with removals of 58 percent and 61 percent for the anthracite filter and the GAC Filter 2, and 79 percent removal for the GAC Filter 3. Color was removed from an average of 4.5 Pt-Co, to below the detection limit (3 Pt-Co) in all filters. Settled water TOC and color increased from the raw water, prior to removal through filtration. As with the initial alum screening, samples were measured for apparent color (i.e., the samples were not filtered prior to color measurement), so some settled water samples showed higher apparent color because of the influence of increased turbidity in the settled water.

ACH was not selected for further testing during the fall season because of short filter run times and turbidity breakthrough, compared to the filter performance with alum and PACl.

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Table 5-5. Average Organics Reduction During the Initial ACH coagulant Screening, July 1–8, 2019 TOC Average Removal Sample Location Average TOC Average Percent Removala No. of Samples Std Dev (mg/L) Raw 0.74 -- 2 0 F1-Anth-72, 8 gpm/sf 0.49 34% 2 0.01 F2-GAC-60, 6 gpm/sf 0.22 70% 2 0.11 F3-GAC-72, 8 gpm/sf 0.15 80% 2 0

Average Reduction of UV254

Sample Location Average UV254 Average Percent No. of Samples Std Dev (cm-1) Reductiona Raw 0.032 -- 4 0.006 F1-Anth-72, 8 gpm/sf 0.012 58% 4 0.011 F2-GAC-60, 6 gpm/sf 0.01 61% 4 0.015 F3-GAC-72, 8 gpm/sf 0.004 79% 4 0.007 a. Average TOC removal and UV254 reduction were determined by averaging the computed daily reduction of TOC and UV254 between paired raw and individual filter effluent samples.

5.1.2.5 Alum and PACl Side-by-side Comparison Following the initial period of coagulant comparison, it was apparent that, under the conditions tested, alum and PACl offered better performance than had been obtained when using ferric chloride or ACH as the primary coagulant. Further evaluation of these two coagulants was conducted with each treating the same water under similar conditions, with PACl in Train 1 (Filters 4, 5, and 6) and alum in Train 2 (Filters 1, 2, and 3). The conditions tested during this side-by-side evaluation are summarized below in Table 5-6. Testing started with coagulant and filter aid, followed by a period of testing that discontinued addition of filter aid but added coagulant aid. Based on an observed degradation in performance without filter aid, the treatment chemicals were adjusted to include filter aid in subsequent testing, regardless of if other treatment chemicals such as coagulants aids were or were not being used in conjunction with the primary coagulant. The coagulant comparison testing concluded with the addition of pre-ozonation to both trains. The following sections present the results from the side-by-side comparison in terms of UFRVs and filter effluent turbidities through July 31, 2019, and UFRVs, filter effluent turbidities, and filter effluent particle counts for the remaining testing scenarios. Organics removal during the side-by-side comparison are summarized for the full comparison testing period at the end of this section.

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Table 5-6. Summary of Chemical Dosing Scenarios for Alum and PACl Comparison Alum (Train 2) PACl (Train 1) c c Test Durationa Coagulant Coagulant Filter Aid Coagulant Coagulant Filter Aid Dose Aidb Dose Dose Dose Aidb Dose Dose (mg/L as Al3+) (mg/L) (mg/L) (mg/L as Al3+) (mg/L) (mg/L) July 15–26, 2019 0.37–0.44 -- 0.01 – 0.03 0.41–0.77 -- 0.01–0.03 (filtration rates at 6 and 8 gpm/sf) July 26–29, 2019 (Start of higher filter rate operation: 0.45 -- 0.02 0.45 -- 0.015 8 and 12 gpm/sf) July 30–August 1, 2019 0.45 0.4–0.6 -- 0.45 0.25–1.0 -- August 1–5, 2019 0.15–0.26 0.5–2.2 -- 0.45 0.25 -- August 5–8, 2019 0.13 0.4 0.015 0.26 0.25 0.015 August 8–12, 2019 0.45–0.62 -- 0.015 0.59 -- 0.015 August 20–30, 2019 0.18 0.4 0.015 0.59 -- 0.015-0.02 (pre-ozonation at 0.5 mg/L) a. A shutdown period occurred from August 12–20 due to mechanical issues with the ozone module. b. Cationic polymer Clarifloc C359 was tested as the coagulant aid. c. Nonionic polymer Clarifloc N-6310 was tested as the filter aid.

Filtration Rates of 6 and 8 gpm/sf The initial round of side-by-side testing was conducted at filtration rates of 6 and 8 gpm/sf, the same filtration rates used for the prior coagulant screening periods. This testing was conducted from July 15 through July 26, 2019, and the calculated UFRVs from this period are presented in Figure 5-11.

The initial side-by-side comparison of alum and PACl presents mixed results. For both the deeper GAC and anthracite filters operating at 8 gpm/sf, the PACl UFRVs are slightly higher than the alum UFRVs. However, the shorter GAC filter operating at 6 gpm/sf with alum addition outperformed the shorter anthracite filter at 6 gpm/sf with PACl addition by a substantial margin. All filters’ median UFRV were above 6,500 gal/sf-run UFRV requirement, while many runs surpassed 10,000 gal/sf-run.

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Figure 5-11. Calculated UFRVs during the side-by-side testing of alum and PACl at 6 and 8 gpm/sf, July 15–26, 2019 Filters 1 is excluded from the figure due to no acceptable filter runs during this time period.

Filter effluent turbidites from both trains during accepted filter runs are summarized below in Figure 5-12. While median turbidity in all filters was below the 0.1 NTU goal, Train 1 (Filters 4 through 6) with PACl had lower turbidities compared to Train 2 with alum (Filters 1 through 3), with the 95th percentile of turbidity in Filter 3, at the 0.1 NTU.

Figure 5-12. Filter effluent turbidities recorded during accepted filter runs during the side-by-side testing of alum and PACl at 6 and 8 gpm/sf, July 15–26, 2019 Filter 1 is excluded from the figure due to no acceptable filter runs during this time period.

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Filtration Rates of 8 and 12 gpm/sf On July 26, 2019, the filtration rates on all filters were increased. The 72-inch filters (Filters 1, 3, 4, and 6) were increased from 8 to 12 gpm/sf, while the 60-inch filters (Filters 2 and 5) were increased from 6 to 8 gpm/sf. Calculated UFRVs from this period are presented in Figure 5-13. The initial runs conducted at filtration rates of 8 and 12 gpm/sf have remarkably consistent UFRVs. All three filters receiving water treated with PACl had higher productivity (e.g., higher UFRVs) than those receiving water treated by alum. As with the preceding condition, the deep GAC filter on the train with alum pretreatment, now operating at 12 gpm/sf, had the lowest UFRV. The other two filters on the alum train (Filters 1 and 2) did not produce any acceptable runs during this period because of excessive turbidity; the filter effluent turbidity from Filter 1 was consistently near or above 0.10 NTU, while the turbidity from Filter 2 was consistently higher than that. In general, operating at higher filtration rates did not appear to impact performance of any of the filters receiving water that had been treated with PACl. All filters on that train surpassed 10,000 gal/sf-run and produced acceptable filtered effluent turbidity. Of the three filters receiving water treated with alum, only the deep GAC filter (Filter 3) produced filter runs that met the acceptance criteria. These runs were generally shorter than those on the other train.

Figure 5-13. Calculated UFRVs during the side-by-side testing of alum and PACl at filtration rates of 8 and 12 gpm/sf, July 26-30, 2019 Filters 1 and 2 are excluded from the figure due to no acceptable filter runs during this time period.

Filter effluent turbidities recorded during this test period are summarized below in Figure 5-14. Effluent turbidities from Filters 1 and 2 are not shown because they exceeded the 0.10 NTU threshold throughout the duration of the filter runs during this period, so none of those runs met the acceptance criteria.

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Figure 5-14. Filter effluent turbidities recorded during accepted filter runs during the side-by-side testing of alum and PACl at filtration rates of 8 and 12 gpm/sf, from July 26 to 30, 2019 Filters 1 and 2 are excluded from the figure due to no acceptable filter runs during this time period.

Without Filter Aid After moving to the higher filtration rates, a brief test period was conducted to determine how the filters would perform without a filter aid. During this time, cationic coagulant aid was dosed between 0.25 to 1.0 mg/L to both trains. This testing was conducted from July 30–August 5, 2019. During this period, a number of runs were terminated early due to operational modifications. Additionally, a number of runs during this period were removed from the dataset because of excessive turbidities. This is attributable either to instrument drift (because of fouling, condensation, etc.) or because the treated water could not be effectively filtered without filter aid. For these reasons, during this period, none of the 12 attempted Filter 1 (anthracite, 12 gpm/sf) runs nor any of the six attempted Filter 2 (GAC, 8 gpm/sf) runs met the criteria for data acceptance. In general, without the addition of filter aid, performance suffered on all filters. As can be seen in Figure 5-15 , filter performance became much less consistent, with a wider spread in UFRVs between filter runs. Filters 1 and 2 are not included on the figure because there were no acceptable filter runs during this time period due to filter effluent turbidities consistently at or above 0.10 NTU.

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Figure 5-15. Calculated UFRVs during side-by-side testing of alum and PACl with no filter aid, July 30-August 5, 2019 Filters 1 and 2 are excluded from the figure due to no acceptable filter runs during this time period.

Figure 5-16 summarizes the filter effluent turbidities recorded during the period comparing alum and PACl coagulation with coagulant aid, but no filter aid. As discussed previously, because of high filter effluent turbidities, neither Filter 1 nor Filter 2 had any accepted runs during this time period.

Figure 5-16. Filter effluent turbidities recorded during accepted filter runs during the side-by-side testing of alum and PACl with no filter aid, July 30-August 5, 2019 Filters 1 and 2 are excluded from the figure due to no acceptable filter runs during this time period

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Figure 5-17 shows two typical runs observed on the 72-inch deep GAC filters (Filters 3 and 4) during this time period. Both runs backwashed based on accumulated head loss, with the alum filter (Filter 3) showing a slight increase in filter effluent turbidity towards the end of the run. However, both filters showed elevated effluent particle counts throughout the runs, with sustained effluent particle counts above 30 particles/mL. This is in contrast to later data, that showed that PACl could effectively limit effluent particle counts to the low single digits throughout the majority of the run when filter aid was applied (see the next section and Section 7.2.3).

Figure 5-17. Filter run examples for coagulant testing without filter aid addition

The particle counters on both Floc/Sed Module 1000 and the Filtration Module were calibrated on July 31, 2019. Thus, this is the first test period during in which reliable particle count data were available. During this test period, there were no accepted runs on Filter 2, and the accepted run on Filter 1 occurred prior to July 31, 2019. For the remaining filters, a summary of filter effluent particle count data is presented in Table 5-7.

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Table 5-7. Particle Counts Summary for Alum and PACl with no Filter Aid, July 31-August 5, 2019 Sampling Location Raw Water Parameter 50th Percentile 95th Percentile Turbidity (NTU) 0.33 0.37

Particles 3 to 5 µm 586 629 (particles/mL) 5 to 15 µm 460 501

Test Condition Train 2: Alum Train 1: PACl 50th 95th Average Log 50th 95th Average Log Parameter Percentile Percentile Removala Percentile Percentile Removala Filter Configuration F1–Anth–72, 12 gpm/sf F6–Anth–72, 12 gpm/sf Turbidity (NTU) ------0.07 0.1 --

Particles 3 to 5 µm ------55 94 1.1 (particles/mL) 5 to 15 µm ------43 78 1.8 Filter Configuration F2–GAC–60, 8 gpm/sf F5–Anth–60, 8 gpm/sf Turbidity (NTU) ------0.06 0.1 --

Particles 3 to 5 µm ------23 60 1.5 (particles/mL) 5 to 15 µm ------24 68 1.1 Filter Configuration F3–GAC–72, 12 gpm/sf F4–GAC–72, 12 gpm/sf Turbidity (NTU) 0.06 0.1 -- 0.06 0.1 --

Particles 3 to 5 µm 33 57 1.4 68 115 1.0 (particles/mL 5 to 15 µm 28 52 1.6 62 102 1.0 a. Average log removals are calculated based on averaging log removals from paired data (raw water and filter effluent for the same aliquot of water based on the HRT) when raw water particles in the indicated size range exceeded 500 particles/mL.

The raw water particle levels were quite low during this time with the 95th percentile in the 5 to 15 µm size range barely exceeding 500 particles/mL. From Table 5-7, it can be seen that none of the filters achieved the performance goal of a 95th percentile ≤50 particles/mL in the 5 to 15 µm size range. The particle count data and the inconsistency in filter UFRVs seen in Figure 5-15 suggests that filter aid could improve performance. Additional Testing with Filter Aid Following the UFRV performance described in the preceding section, the decision was made to switch back to filter aid for additional side-by-side testing. These additional runs, conducted from August 5 to 12, 2019, are presented in Figure 5-18.

Compared to the initial period of higher filtration rate testing, the runs conducted from August 5 to 12 were less consistent. Filters 3, 4, and 5 had median UFRVs at or below the 10,000 gal/sf goal with large variation in Filter 3 and Filter 5.

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Figure 5-18. Calculated UFRVs during side-by-side testing of alum and PACl with filter aid, August 5-12, 2019 Figure 5-19 summarizes the corresponding filter effluent turbidity data recorded during the filter runs shown in Figure 5-18. Overall, filter effluent turbidities were quite good, with median effluent turbidities at or below 0.05 NTU for all filters. The train with PACl pretreatment produced particularly low filter effluent turbidities.

Figure 5-19. Filter effluent turbidities recorded during accepted filter runs during the side-by-side testing of alum and PACl with filter aid, August 5-12, 2019 A summary of the particle count data collected during this test period, from August 5 to 12, 2019, is presented in Table 5-8. Compared to the preceding test period, filter effluent particle counts are lower than the particle counts presented in Table 5-7, supporting the benefit of filter aid on filter performance. All of the filters produced excellent water quality and met the particle count goal of being less than 50 particles/mL for the 5 to 15 µm range. Raw water

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particle counts were quite low during this test period, so even though all of the filters met the particle count goal of being less than 50 particles/mL for the 5 to 15 µm range, only the 60-inch anthracite filter operating at 8 gpm/sf (Filter 5) was able to demonstrate 2.5-log particle removal. At least 2-log removal of particles in the 3 to 5 µm range was achieved by four of the six filters. Table 5-8 demonstrates the excellent water quality produced at this time.

Table 5-8. Particle Counts Summary from Side-by-Side Testing of Alum and PACl, August 5-12, 2019 Sampling Location Raw Watera Parameter 50th Percentile 95th Percentile Turbidity (NTU) 0.45 0.55

Particles 3 to 5 µm 555 625 (particles/mL) 5 to 15 µm 415 483

Test Condition Train 2: Alum Train 1: PACl 50th 95th Average Log 50th 95th Average Log Parameter Percentile Percentile Removala Percentile Percentile Removala Filter Configuration F1–Anth–72b, 12 gpm/sf F6–Anth–72b, 12 gpm/sf Turbidity (NTU) 0.05 0.07 -- 0.01 0.02 --

Particles 3 to 5 µm 11 26 1.7 5 14 2.0 (particles/mL) 5 to 15 µm 6 26 1.9 2 8 1.9 Filter Configuration F2–GAC–60, 8 gpm/sf F5–Anth–60, 8 gpm/sf Turbidity (NTU) 0.03 0.03 -- 0.01 0.07 --

Particles 3 to 5 µm 4 5 2.1 4 9 2.1 (particles/mL) 5 to 15 µm 2 4 -- 2 4 2.5 Filter Configuration F3–GAC–72, 12 gpm/sf F4–GAC–72, 12 gpm/sf Turbidity (NTU) 0.04 0.06 -- 0.02 0.03 --

Particles 3 to 5 µm 11 35 1.7 5 14 2.0 (particles/mL) 5 to 15 µm 6 40 1.8 3 8 1.9 a. Average log removals are calculated based on averaging log removals from paired data (raw water and filter effluent for the same aliquot of water based on the HRT) when raw water particles in the indicated size range exceeded 500 particles/mL.

Evaluation of Coagulant Performance with Pre-oxidation The final coagulant selection test evaluated alum and PACl side-by-side with pre-oxidation using ozone. The goal for this test was to determine if one coagulant was more effective when the raw water organics were transformed via pre-oxidation. This testing was conducted from August 20 to 30, 2019, during which both trains received water that had been pre-oxidized with an applied ozone dose of 0.5 mg/L. Pre-oxidation along with adjustment of coagulant dosages significantly improved filter UFRVs, as shown below in Figure 5-20. Except for one run on Filter 1 and one run on Filter 3, all filters surpassed 10,000 gal/sf-run. UFRVs for Filter 3 (GAC, 12 gpm/sf)) had UFRVs more than double

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from the preceding test period when filter aid was not used. In general, the UFRVs were higher in the filters receiving water treated with alum when compared to the filters treated with PACl.

Figure 5-20. Calculated UFRVs during side-by-side testing of alum and PACl following ozone pre-oxidation, August 20-30, 2019 Filter effluent turbidities recorded during the accepted runs during this period are shown in Figure 5-21. Filters 2 through 6 generally produced lower turbidity water, with median filter effluent turbidities near or below 0.03 NTU. Filter 1 had consistently higher filter effluent turbidities, with a median near 0.08 NTU.

Figure 5-21. Filter effluent turbidities recorded during accepted filter runs during side-by-side testing of alum and PACl following ozone pre-oxidation, August 20-30, 2019

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Particle count data collected during this test period are summarized in Table 5-9. Particle counts were well controlled. All filters had greater than 2.0-log removal for the 3 to 5 µm range and greater than 2.5-log for the 5 to 15 µm range. Log removals are expected to be conservative because the calculation is based on a comparison of pre-ozonated water to filtered water. Pre-ozonation was found to decrease particle count levels in the filtered water. Particle counts out of the 12 gpm/sf filters on Train 2 (Filters 1 and 3) were generally higher than Filters 4 and 6.

Table 5-9. Pre-ozonated Water and Filter Effluent Particle Counts Summary from Side-by-Side Testing of Alum and PACl, August 20–30, 2019 Sampling Location Pre-ozonated Watera Parameter 50th Percentile 95th Percentile Turbidity (NTU) 0.31 0.91 Particles 3 to 5 µm 427 490 (particles/mL) 5 to 15 µm 197 222 Test Condition Train 2: Alum Train 1: PACl 50th 95th Average Log 50th 95th Average Log Parameter Percentile Percentile Removala Percentile Percentile Removala Filter Configuration F1–Anth–72, 12 gpm/sf F6–Anth–72, 12 gpm/sf Turbidity (NTU) 0.08 0.10 -- 0.01 0.04 -- Particles 3 to 5 µm 6 24 2.3 0 29 2.7 (particles/mL) 5 to 15 µm 5 24 2.8 0 25 2.7 Filter Configuration F2–GAC–60, 8 gpm/sf F5–Anth–60, 8 gpm/sf Turbidity (NTU) 0.02 0.03 -- 0.01 0.04 -- Particles 3 to 5 µm 1 2 2.7 0 1 2.7 (particles/mL) 5 to 15 µm 0 6 2.8 0 0 2.8 Filter Configuration F3–GAC–72, 12 gpm/sf F4–GAC–72, 12 gpm/sf Turbidity (NTU) 0.03 0.06 -- 0.02 0.07 -- Particles 3 to 5 µm 10 41 2.2 0 1 2.7 (particles/mL) 5 to 15 µm 12 46 2.6 0 0 2.8 a. Average log removals are calculated based on averaging log removals from paired data (ozonated water and filter effluent for the same aliquot of water based on the HRT) when ozonated water particles in the indicated size range exceeded 500 particles/mL. Log removals are expected to be conservative because the calculation is based on a comparison of pre- ozonated water to filtered water. Ozonation was shown to decrease particle count levels.

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Organics Removal from Side-by-Side Comparison Organics removal between the alum and PACl trains were comparable on average between the side-by-side comparison testing, with slight differences in percent removals for the initial testing with low filtration rates and during the high filtration rate testing.

Tables 5-10 and 5-11 show the TOC and UV254 data through the alum and PACl side-by-side comparison period from July 16 to August 30. As mentioned previously, for TOC results less than the MRL, the value was reported as half the MRL (0.15 mg/L). On average across the side-by-side coagulant testing period, the anthracite filter removed TOC by about 34 percent in the alum fed train and by 42 percent in the PACl fed train. After filter aid was stopped and coagulant aid dosing of 0.25 mg/L started on July 30, 2019, there was an increase in TOC in the GAC filters with a larger increase in the train with alum. When filter aid was added again on August 5, TOC results were below the MRL for the GAC filter, and UV254 reduced for all filters, demonstrating the benefit of filter aid addition to improve filterability. Color was reduced from an average of 4.6 Pt-Co to below the MRL for all filters.

Table 5-10. Average TOC Removal During Alum and PACl Side-by-Side Comparison, July 16–August 30, 2019

Test Sampling TOC Average Removal Condition Location Average TOC (mg/L) Average Percent Removala Number of Samples Std Dev Raw Water 0.74 -- 17 0.03 F1-Anth-72 0.49 34% 14 0.06 Train 2: Alum F2-GAC-60 0.24 68% 16 0.10 F3-GAC-72 0.28 62% 14 0.11 F4-GAC-72 0.16 77% 16 0.04 Train 1: PACl F5-Anth-60 0.42 43% 15 0.05 F6-Anth-72 0.43 42% 16 0.05 a. Average TOC removal was determined by averaging the computed daily removal of TOC between raw and individual filter effluent.

Table 5-11. Average Reduction of UV254 During Alum and PACl Side-by-Side Comparison, July 15– August 30, 2019

Average Reduction of UV254 Test Sampling -1 Average Percent Condition Location Average UV254 (cm ) Number of Samples Std Dev Reductiona Raw Water 0.029 -- 25 0.006 F1-Anth-72 0.013 62% 19 0.009 Train 2: Alum F2- GAC-60 0.010 73% 22 0.011 F3-GAC-72 0.004 86% 21 0.004 F4-GAC-72 0.003 87% 21 0.004 Train 1: PACl F5- Anth-60 0.009 74% 19 0.003 F6-Anth-72 0.007 77% 20 0.003

a. Average reduction of UV254 was determined by averaging the computed daily reduction of UV254 between raw and individual filter effluent.

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5.2 Coagulation

After selecting PACl as the primary coagulant to be used during pilot testing, the pilot team developed and continued to refine coagulation operations throughout the duration of the pilot. At the beginning of the pilot study, the only signal to demonstrate the effectiveness of coagulation was filter performance. After a month of operations, a portable on-line SCM instrument was obtained from CHEMTRAC to allow for monitoring SCM immediately post- coagulation on one floc/sed train. This instrument was moved between the two trains on a regular basis until a permanent SCM was installed on October 29, 2019. Feed tubing was routed from both trains to the permanent SCM to allow it to monitor either train, although it still could only measure one train at a time.

As previously mentioned, the SCM, a bench-top zeta potential instrument was evaluated in early October and rented for use at the pilot starting in late March 2020. The following section evaluates the effectiveness of both the SCM and zeta potential in controlling coagulation.

This pilot effort focused on charge neutralization as the coagulation mechanism and the pilot team observed that the Bull Run water is highly sensitive to coagulant and coagulant aid chemical dosages. There is little charge in the source water to start with, and so over- or under- feeding coagulant by as little as a few tenths of a mg/L can significantly impact the effectiveness of coagulation, with negative impacts to the downstream treatment processes. It is recommended that the full-scale facility be designed to allow for a fine-level of control over chemical dosing.

5.2.1 Summary of Pilot Coagulant Comparison

Based on initial coagulant screening, alum and PACl demonstrated adequate performance while ACH and ferric were difficult to find conditions that met the pilot water treatment goals. More extensive side-by-side evaluations of alum and PACl were conducted. Filtration rates were increased to 12 gpm/sf in the deeper filters (8 gpm/sf in the shorter filters) without any adverse impact on performance.

In general, there was no clear performance difference between alum and PACl. Filter productivity was slightly higher with PACl when pre-oxidation was not applied, and somewhat higher with alum when pre-oxidation was implemented; the GAC filter columns saw an increase in UFRVs, but the anthracite column did not. With both coagulants, filter productivity and filter effluent particle counts met performance goals, provided that filter aid was also used. Without filter aid, filtration could meet turbidity goals, but neither coagulant was capable of meeting filter effluent particle count goals. Overall, organics removal was comparable between the two trains through the testing period with neither coagulant performing significantly better than the other for all organic parameters evaluated (i.e., TOC, UV254, and color).

Based on these initial results, the decision was made to use PACl as the primary coagulant for subsequent testing. This decision was made primarily on operational grounds; while performance was similar between both alum and PACl, alum required more careful monitoring of raw water alkalinity and required feeding supplemental alkalinity (in the form of sodium

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bicarbonate) at higher alum doses. Operating with a sufficiently high pH was a consideration for this pilot study because of the discharge required to be pH greater than 6. Because PACl is less sensitive to alkalinity, it was easier to maintain PACl coagulation at the pilot.

During the turbidity spiking study, PACl and alum were both tested as coagulants. The results from this study are discussed in Section 5.6. Following the turbidity spiking study, the pilot was operated with alum as the primary coagulant for a 5-day period. During this time, filtration performance was also good, with low filter effluent turbidity and particle counts and UFRVs surpassing 10,000 gal/sf-run (excluding filter runs with chemical dosing problems).

5.2.2 Evaluating Effectiveness–Zeta Potential and SCM

This section describes the use of both a SCM and zeta potential analyzer in monitoring coagulation conditions during April 2020. Figure 5-22 shows the zeta potential and SCM readings for the month, along with the coagulant and coagulant aid doses at the time.

Figure 5-22. Comparison of zeta potential and SCM observations relative to coagulation chemical dosage

The value of the SCM as an online instrument is shown through its continuous measurements. However, the SCM readings also exhibit considerable variation despite relatively consistent raw water quality and coagulation dosing, suggesting the SCM is less reliable with changes in water

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quality. The SCM was last calibrated in a season of differing raw water quality, such that the target for charge neutralization had drifted from an SCM reading around 0 to one around +100 at the beginning of the period shown. For that reason, the SCM was recalibrated on April 24 so the target could be returned to approximately 0 SCU. An error entering instrument settings caused the output readings to become significantly negative on April 25, which was subsequently fixed on April 27. In comparison, the Zetasizer readings on both trains during this period remained within a fairly tight band between 0 and -5 mV. Although the Zetasizer readings were more consistent, they were only available periodically when grab samples were taken.

Figure 5-23 shows the same data, but directly compares the zeta potential and SCM readings for the reporting period. The data were separated into two sets, differentiating by whether the samples were collected before or after the SCM instrument was recalibrated on April 24 by offsetting the measurement of the neutral charge condition by 100 units.

Figure 5-23. Correlation of zeta potential and SCM readings during April 2020

As shown Figure 5-23, there is a linear relationship between the readings between the zeta potential and SCM both before and after the offset. Prior to recalibration of the SCM, the SCM readings between 110–140 SCU corresponded to 0 mV on zeta potential. This is very different than previous readings collected during the pilot study that found SCM readings of 25 SCU corresponded to a 0 mV zeta potential as measured by the Zetasizer (also a Malvern Panalytical NanoZ) being evaluated during that period. However, at that time, the pilot was feeding approximately 3 mg/L of PACL without any coagulant aid, compared to the coagulant and coagulant aid doses used during this period (as shown in Figure 5-22). This variation indicates that SCM is more susceptible to seasonal variation when targeting charge neutralization. The instrument required periodic checking/re-calibration by a benchtop zeta potential analyzer to

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maintain a correlation between an SCM reading of 0 SCU and a zeta potential of 0 mV. In the absence of an instrument to measure zeta potential, filter performance and/or jar testing was needed to determine the range of SCM readings that correspond to treatment that meets the target performance goals.

Other findings from previous and current comparison of these two instruments is as follows: • As an online monitoring tool, the SCM could help in quickly determining a chemical feed flow loss or an overdose, or a rapidly changing source water condition, which would not be automatically caught by a benchtop zeta potential instrument. • Zeta potential is a tool that provides more reproducible results, because it measures an inherent property of the water (the zeta potential of the colloidal suspension). Zeta potential measurements can be reproduced and compared with other studies, other pilot projects, or even within this pilot over time, which would be useful when comparing different coagulant types and doses. • The zeta potential reading is affected by fewer variables making it a more reliable technique to measure the particle charge. Furthermore, according to the SCM manual, the more variable the water chemistry is in terms of pH, alkalinity, conductivity and temperature, the SCM reading will become less reliable as a control tool. • The offset settings on the SCM should be periodically adjusted with seasonal changes to target new setpoints for coagulation dosing. • During this monitoring period, a strong correlation between SCM and zeta potential readings was observed. However, this correlation depends on the water quality used to calibrate the neutral charge on the SCM. As water quality changes, the numerical correlation between the SCM and zeta potential readings also changes (even if the overall correlation between the measurements is consistent). The SCM’s relative measurement can be countered either by recalibrating the instrument to set 0 SCU to match a 0 mV zeta potential (which requires comparison against the zeta potential) or by using filter performance and/or jar testing to establish the target range where the SCM should be maintained based on seasonal water quality.

5.3 Flocculation

This section provides an overview of operational changes made to the flocculation process, including the detention time and mixing velocities of the three basins. Flocculation was kept relatively consistent for the majority of the pilot test duration, with slight variations shown in Table 5-13. Three flocculation basins were used for all standard testing conditions such as pre- ozonation, intermediate-ozonation, conventional filtration, and direct filtration.

The detention time was adjusted slightly due to the hydraulic configuration of the pilot. For example, when a train was configured for intermediate ozonation, the detention time was slightly longer than when configured for pre-ozonation due to the different flow rates to each skid. The typical detention times are summarized in Table 5-12.

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Table 5-12. Flocculation Detention Times Dependent on Operational Configuration Condition Influent Water Flow (gpm) Detention Time (min) Pre-ozonation 8.0–8.5 33–35 Intermediate-ozonation 9.0–9.5 30–31

Along with the detention time changes during standard operational periods, flocculation mixing velocities were altered. These changes are summarized in Table 5-13. The adjustments did not result in any noticeable change in flocculation.

Table 5-13. Flocculation Mixing Velocity Changes, June 2019-June 2020 Flocculation Basin 1 Flocculation Basin 2 Flocculation Basin 3 Testing Period Velocity Gradient (s-1) Velocity Gradient (s-1) Velocity Gradient (s-1) June 1–November 8, 2019 75 50 25 November 8, 2019– 80 60 40 February 24, 2020 February 24–May 27, 2020 40 30 25 May 27–June 4, 2020 40 40 30 June 5–June 8, 2020 50 30 24 June 8–June 30, 2020 60 40 25

During the turbidity spiking from June 3–12, 2020, further details provided in Section 5.6, the detention time was also altered. For this unique testing period, only two filters were operated for each train, resulting in 5.2 gpm influent water and a detention time of 55 minutes.

5.4 Coagulant Aid

This section describes the impact of coagulant aid addition on filter productivity and the trade- off between coagulant and coagulant aid during the pilot study, with a specific focus on operations in mid-January when coagulant aid was added to the chemical dosing strategy after several months with coagulant and filter aid only.

Coagulant and coagulant aid chemicals were dosed at the rapid mix system to facilitate colloidal destabilization, followed by flocculation and sedimentation. As described in Section 5.1.1 above, based on initial jar testing and comparison to other water treatment facilities in the region, coagulant aid was suggested as a possible addition to improve the coagulation process. For pilot testing, cationic polymer Clarifloc C-359 was selected based on performance in bench- scale testing and availability from a local supplier. It is also used at a full-scale treatment facility operated by another water provider in the region.

Based on the side-by-side comparison testing, as discussed in Section 5.1 above, it appeared coagulant aid did not provide a benefit for coagulation with PACl, and was not used during the summer to early winter testing (August through mid-January). During that time, the PACl dose ranged from 0.59 to 0.82 mg/L as Al3+, with a filter aid dose starting at around 0.01 mg/L, followed by a transition to a higher dose of between 0.02 to 0.05 mg/L.

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Starting in mid-December and into January, filter efficiency was moderate with UFRVs between 6,500 gpm/sf and 10,000 gpm/sf, compared to previous testing periods when filter UFRVs were above the 10,000 gpm/sf performance goal on average. Performance indicated a need to adjust the chemical dosing strategy through the addition of coagulant aid.

In order to understand the impact from the coagulant aid addition, both trains were tested with the same pretreatment condition of pre-ozone with 1.0 mg/L as O3 starting on January 21, 2020. Operations were adjusted to add a coagulant aid dose of 0.25 mg/L, PACL dose of 0.77 mg/L as Al3+ and filter aid dose of 0.04 mg/L on Train 1, and 0.40 mg/L coagulant aid, 0.77 mg/L as Al3+ and 0.02 mg/L filter aid on Train 2. After 2 days, the coagulant dose was reduced in both trains to 0.51 mg/L as Al3+, and was further reduced after another 4 days of testing to 0.34 mg/L as Al3+ in both trains along with an increase in coagulant aid to 0.53 mg/L for Train 1 and 0.52 mg/L for Train 2. Optimization of the dosing strategy demonstrated an inversely proportional relationship between coagulant and coagulant aid dosing, indicating a lower dose of coagulant is acceptable when paired with coagulant aid.

After 2 weeks of operations, there was a clear improvement in filter productivity with coagulant aid. All filters saw higher run times and UFRVs with coagulant aid. Figures 5-24 and 5-25 compare filter run hours and UFRVs, respectively, from before coagulant aid addition (January 1 to 21) and after the addition of coagulant aid (January 21 through February 3). However, the median run times/UFRVs in Filters 1 and 3 were slightly lower because it took a few days to discover adequate coagulant and coagulant aid doses, during which time filter runs were generally short. This time required to improve coagulation is reflected in the range of run times and associated UFRVs seen in Figure 5-24 and Figure 5-25 by the length of the box. Additionally, run time was limited by filter aid dosing to three filters at a time. In general, filter productivity improved over the duration of the test period as coagulation conditions were improved further.

Figure 5-24. Filter run hours by filter during pre-oxidant testing (January 1–21) and after the addition of coagulant aid (January 21–February 3)

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Figure 5-25. Calculated UFRVs by filter during pre-oxidant testing (January 1–21) and after the addition of coagulant aid (January 21–February 3)

Figure 5-26 shows the filter effluent turbidities recorded during accepted filter runs during the two test periods. Median filter effluent turbidities were slightly lower in Filters 1 and 3 while staying the constant in Filter 2 after the addition of coagulant aid. During these test periods, the filter effluent turbidities were below the limit of 0.1 NTU for more than 95 percent of the operational time.

Figure 5-26. Filter effluent turbidities recorded during accepted filter runs during pre-oxidant testing (January 1–21) and after the addition of coagulant aid (January 21–February 3)

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In addition to filter productivity, particle counts were generally lower with coagulant aid (Table 5-14). The 95th percentile particle counts in the 5 to 15 µm range were between 11 to 68 particles/mL without coagulant aid and between 2 to 12 particles/mL with the addition of coagulant aid. The difference is most clear when comparing by filter. For example, Filter 1’s (F1-Anth-72) 95th percentile particle counts were 56 particles/mL without coagulant aid, and 12 particles/mL with coagulant aid. The same trend was observed for Filters 2 and 3 as well. During this testing period, the pre-ozonated with coagulant aid filters (Filters 1 through 3) met the goal of having less than 50 particles/mL in the 5 to 15 µm range.

Table 5-14. Raw and Ozonated Water and Filter Effluent Particle Counts During Pre-Oxidant Testing Before (January 1 to 21) and After the Addition of Coagulant aid (January 21 to February 3) Particle counts (particles/mL)

Test Sampling 3 to 5 µm 5 to 15 µm Test Date Condition Location th th th th 50 95 Log 50 95 Log a a percentile Removal percentile Removal None Raw water 955 1,080 -- 655 761 -- Jan 1 – 21, F1-Anth-72 0 44 2.6 0 56 2.4 2020 Pre-ozonation F2-GAC-60 1 54 2.5 1 68 2.3 F3-GAC-72 0 10 2.8 0 11 2.6 None Ozonated waterb 705 919 -- 411 596 --

Jan 21 – Feb 3, Pre-ozonation F1-Anth-72 1 10 2.7 0 12 2.7 2020 with coagulant F2-GAC-60 0 2 2.8 1 2 2.6 aid F3-GAC-72 1 2 2.8 0 2 2.7 a. Log removals calculated based on paired data when raw or ozonated water particles in the indicated size range exceed 500 particles/mL. NA is shown if there were insufficient raw water particles >500 particles/mL during the period indicated. b. Train 1 was ozonated during this period, therefore particle counts are post-ozonation. Particle counts may be lower than would be expected in untreated raw water. Log removals are conservative as a result.

Prior to coagulant aid addition, TOC removal from raw water to filtered effluent was excellent from January 1 to 21, with removals between 56 and 67 percent. Color reduction was also excellent with reductions below the MRL. A slight increase in TOC in the filtered effluent was observed at the same time as a slight decrease in raw water TOC around the start of the coagulant addition on January 21. The increase in TOC, without a corresponding increase in raw water, indicates there was a slight decrease in organics removal with the addition of coagulant aid (from an overall average removal of 62 percent down to an average of 52 percent). Color removal decreased slightly as well with the coagulant aid addition; however, that is not significant given that color was reduced to below the MRL for all filters.

UV254 reduction was not impacted by coagulant aid addition, showing a reduction from raw to -1 filtered effluent over 85 percent for all samples from an average raw filtered UV254 of 0.05 cm to an average of 0.007 cm-1 in the filtered effluent with minimal standard deviation in results.

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Coagulant Aid Water Quality Considerations The addition of a coagulant aid polymer in combination with PACl was found to improve filter productivity. One consideration for the use of coagulant aid polymers is the potential to contribute chemical precursors that could later react with chloramines to form nitrosamine compounds, a group of disinfection byproducts that are not currently regulated by the EPA but could be in the future due to potential health impacts. In April 2020, during a period of pilot operation that included the use of a coagulant aid polymer at a dose of 0.3 mg/L, a bench-scale SDS test was conducted to evaluate the potential for nitrosamine formation. The SDS test involved collecting samples from the pilot raw inlet and pilot filtered effluents, providing a free chlorine contact period followed by chloramination and corrosion control treatment to mimic the post-filtration treatment process, and then analyzing water quality at the beginning and end of a 14-day SDS incubation period. Very low levels of the nitrosamine compound N-Nitrosodimethylamine (NDMA) were detected in the 14-day chloraminated filter effluent samples. No nitrosamine compounds were detected in any other samples analyzed during the test. Detailed results for the test are included in the April SDS Evaluation Technical Memorandum Appendix B. PWB plans to conduct optimization studies to further evaluate this issue and will determine mechanisms to reduce the formation of nitrosamines in the finished water from the future filtration facility.

5.5 Sedimentation

This section reviews the impact of a SLR adjustment and provides an overview of testing done that investigated the benefit of the sedimentation process. Throughout the duration of pilot testing, flocculation was kept consistent for the majority of the time. Three flocculation basins were used for all standard testing conditions such as pre-ozonation, intermediate-ozonation, conventional filtration, and direct filtration. While SLRs were varied throughout this study, SLR is not a variable that scales well from pilot-scale to full-scale and so therefore, the values piloted should not limit the design of the full-scale sedimentation process.

Figure 5-27 shows settled water turbidity from November 18, 2019 to January 6, 2020. On December 17, 2019, the SLR was reduced in both trains from 0.3 gpm/sf to 0.2 gpm/sf. For the SLR modification, eight settling plates were added to the settling basin, resulting in 24 plates/train and an SLR of 0.2 gpm/sf at a flow rate of 8.5 gpm/train. Despite the decrease in the SLR, the settled water turbidity remained relatively constant during the test period, and increased slightly.

There was a period from approximately December 4 to December 12, 2019, when the human- machine interface (HMI) indicated an apparent drop in settled water turbidity; however, this was not supported by the grab samples collected during this period and is thought to be an issue with the pump supplying water to the instrument being off.

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Figure 5-27. Comparison of Train 1 HMI and grab samples settled water turbidity to raw water grab samples turbidity, November 18, 2019-January 6, 2020 Throughout pilot testing, the pump that supplied the turbidimeters resulted in an increase variability, as seen in both Train 1 (Figure 5-27, above) and Train 1 (Figure 5-28, below). Figure 5-28 presents the settled water turbidity for Train 1 (grab and online turbidimeter) for the pilot operational period. Excluding the turbidity spiking study, settled water turbidity surpassed the goal of the 95th percentile of data being less than 2 NTU. The 95th percentiles for the grab samples’ settled water turbidities were 1.3 and 1.5 NTU for Trains 1 and 2, respectively.

Figure 5-28. Comparison of Train 1 HMI and grab samples settled water turbidity, July 1, 2019-May 31, 2020

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In mid-October, the settled water turbidity in Train 1 increased. This correlates with the introduction of prechlorination on that train. Settled water turbidity decreased below 1 NTU after March, when pre- oxidation was discontinued on Train 1.

5.6 Direct Filtration Testing

Direct filtration was tested during the following operational periods: • September 30–October 11, 2019: Direct filtration, pre-ozonation (Train 1) and conventional filtration, pre-ozonation (Train 2) • June 16–June 30, 2020: Direct filtration, intermediate-ozonation (Train 1) and direct filtration, pre-ozonation (Train 2), as shown in Figure 5-29

Figure 5-29. Treatment train for direct filtration treatment testing, June 16-June 30, 2020

Although direct filtration was attempted during September to October, the results during this period were not representative of anticipated operations because of difficulties with chemical dosing strategy and limitations with filter aid dosing location. The majority of the filter runs in the direct filtration train terminated due to turbidity exceeding the backwash trigger (≥0.15 NTU) instead of head loss exceeding the backwash trigger (≥12 feet). This behavior was unexpected. Direct filtration appeared to produce floc that was not captured through filtration, and led to higher turbidity in the filter effluent, because of the nature of the floc particles and related to the filter aid dose inconsistencies.

It was noted during this initial direct filtration evaluation that visual observation of the floc suggested the size of the flocs being developed was larger than optimum for direct filtration. After analyzing the data for this attempt at direct filtration, small floc size was identified as an operational goal. In direct filtration testing completed June 16–30, 2020, adjustments were made to stabilize filter aid dosing locations, adjust chemical dosing to achieve a smaller floc size, and evaluate their impact on floc formation and related filter performance. The data presented in this section are based on operation from June 2020.

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5.6.1.1 Turbidity Turbidity data, during low influent turbidity, for the direct filtration test period are summarized in a box-whisker plot in Figure 5-30. Both direct filtration treatment trains (one with pre- ozonation and one with intermediate ozonation) surpassed the water quality goal to have the filter effluent turbidity at less than 0.1 NTU, 95 percent of the time. The intermediate ozonation train had lower filter effluent turbidity; 95 percent of the filter effluent turbidity was at or below 0.025 NTU. The filter effluent turbidity was greater with greater filtration rates for the filters with pre-ozonation (Train 2).

Figure 5-30. Filter effluent turbidity for direct filtration testing with pre-ozonation and intermediate-ozonation, June 18-30, 2020 Both pre-ozonation and intermediate ozonation trains surpassed turbidity goals with consistent, low filter effluent turbidity and particle counts. Typical filter runs for both intermediate and pre-ozone are shown in Figure 5-31 with Filter 2 and Filter 5, both operating at 10 gpm/sf, having runs over 20 hours.

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Figure 5-31. Filter run examples for direct filtration

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5.6.1.2 Particle Counts Particle counts and log removals from June 18–30 are summarized below in Table 5-15. All filters surpassed the direct filtration particle removal goal of achieving 2.0-log removal in 3 to 5 µm and 5 to 15 µm. Except for Filters 1 and 2 (pre-ozonation), all filters had 95th percentile particle counts less than 50 particles/mL. The 50th percentile particle counts were very low for all filters. Both direct filtration trains had low particle count levels, but intermediate ozonation had higher particle count average log removals and lower filter effluent particle count levels.

Table 5-15. Particle Counts Summary from Direct Filtration Testing, June 18–30, 2020 Sampling Location Raw Water Parameter 50th Percentile 95th Percentile Turbidity (NTU) 0.29 0.33

Particles 3 to 5 µm 616 686 (particles/mL) 5 to 15 µm 464 523 Test condition Train 2: Pre-ozonation, Direct Train 1: Direct, Intermediate ozonation 50th 95th Average Log 50th 95th Average Log Parameter Percentile Percentile Removala Percentile Percentile Removala Filter Configuration F1-Anth–60, 8 gpm/sf F6-Anth–60, 8 gpm/sf Turbidity (NTU) 0.01 0.03 -- 0.01 0.02 --

Particles 3 to 5 µm 1 131 2.5 1 3 2.7 (particles/mL) 5 to 15 µm 1 109 2.6 1 4 2.7 Filter Configuration F2-Anth–66, 10 gpm/sf F5-Anth–66, 10 gpm/sf Turbidity (NTU) 0.01 0.04 -- 0.02 0.02 --

Particles 3 to 5 µm 2 145 2.2 1 2 2.7 (particles/mL) 5 to 15 µm 2 136 2.2 1 3 2.7 Filter Configuration F3-Anth–72, 12 gpm/sf F4-Anth–72, 12 gpm/sf Turbidity (NTU) 0.01 0.05 -- 0.01 0.01 --

Particles 3 to 5 µm 1 30 2.5 1 9 2.7 (particles/mL) 5 to 15 µm 1 24 2.3 1 6 2.6 a. Average log removals are calculated based on averaging log removals from paired data (raw water and filter effluent for the same aliquot of water based on the HRT) when raw water particles in the indicated size range exceeded 500 particles/mL.

5.6.1.3 Filter Run Time and UFRVs Filter run time plots are provided to help understand the impact to operations. The filter run times presented correspond to the UFRV data presented in this report. The filter run time and calculated UFRVs comparing pre-ozonation and intermediate ozonation are presented below in Figure 5-32 and Figure 5-33, respectively. As expected, filter run times were proportional to filtration rate with the greatest filter run times corresponding to the lowest filtration rates. The 8 and 10 gpm/sf filters had run times in excess of 20 hours.

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UFRVs were comparable between the 8 and 10 gpm/sf filters. In general, intermediate ozonation had higher filter run times and UFRVs. All filters, except Filter 3, had UFRVs in excess of 10,000 gal/sf-run. The performance of Filter 3 was impacted by this filter having a higher initial CBHL than Filter 4. CBHL is discussed in detail in Section 7.2.1.

Figure 5-32. Filter run times for direct filtration testing with pre-ozonation and intermediate-ozonation, June 11–30, 2020

Figure 5-33. UFRVs for direct filtration testing, June 11–30, 2020

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Figure 5-34 and Figure 5-35 compare the direct filtration operation in June to performance in May when the same oxidation strategy was in place, but conventional filtration (conventional treatment) was in operation. Through these plots, one can evaluate the impact of conventional filtration or having sedimentation. The figures present direct and conventional filtration with intermediate ozonation and pre-ozonation, respectively. Conventional filtration improved UFRVs in both intermediate and pre-ozonation operational schemes from 20 to 39 percent across all the filters, with the highest percent improvement observed in Filter 3. Direct filtration showed good operational performance and excellent water quality, but conventional filtration improved treatment performance further by extending filter run times.

Figure 5-34. UFRVs for conventional filtration (April 30 to May 12, 2020) and direct filtration (June 18–June 30, 2020) with intermediate-ozonation

Figure 5-35. UFRVs for conventional filtration (April 30 to May 12, 2020) and direct filtration (June 18-June 30, 2020) with pre-ozonation

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5.6.1.4 Organics Removal

This section presents TOC, UV254, and color data during direct filtration testing. Table 5-16 presents the TOC data for raw water and filter effluent. Typically, all treatment schemes removed about 50 percent of the TOC. In general, pre-ozonation removed slightly more TOC.

Table 5-16. Average TOC Removal During Direct Filtration Operation, June 18-30, 2020 TOC Average Removal Pretreatment Sample Location Average TOC Average Percent Condition No. of Samples Std Dev (mg/L) Removala Raw Water 0.99 -- 3 0.02 F1-Anth-60, 8 gpm/sf 0.46 54% 3 0.03 Pre- F2-Anth-66, 10 gpm/sf 0.47 53% 3 0.01 ozonation F3-Anth-77, 12 gpm/sf 0.45 54% 3 0.02 F4-Anth-72, 12 gpm/sf 0.51 48% 3 0.02 Intermediate F5-Anth-66, 10 gpm/sf 0.54 45% 3 0.07 Ozonation F6-Anth-60, 8 gpm/sf 0.52 48% 3 0.03 a. Average TOC removal was determined by averaging the computed daily removal of TOC between raw and individual filter effluent.

Table 5-17 presents the UV254 data for the direct filtration operation. The pre-ozonation treatment train removed 87 to 89 percent of UV254 on average, and intermediate ozonation removed 87 percent on average.

Table 5-17. Average UV254 Reduction During Direct Filtration Operation, June 18-30, 2020

Average Reduction of UV254 Pretreatment Sample Location Condition Average Average Percent a No. of Samples Std Dev UV254 (UVA) Reduction Raw Water 0.045 -- 6 0.003 F1-Anth-60, 8 gpm/sf 0.006 88% 7 0.002 Pre-ozonation F2-Anth-66, 10 gpm/sf 0.006 88% 6 0.001 F3-Anth-77, 12 gpm/sf 0.005 89% 6 0.001 F4-Anth-72, 12 gpm/sf 0.005 87% 6 0.001 Intermediate F5-Anth-66, 10 gpm/sf 0.006 87% 5 0.001 Ozonation F6-Anth-60, 8 gpm/sf 0.006 88% 6 0.001 a. Average reduction of UV254 was determined by averaging the computed daily reduction of UV254 between raw and individual filter effluent.

The raw water color levels averaged 7.3 Pt-Co units and ranged from 6.3 to 8.3 Pt-Co units. All of the filter effluent color levels were below the MRL of 3 Pt-Co units for each of the five sampling events.

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5.7 Turbidity Spiking Study

A naturally occurring elevated-turbidity event did not occur during the pilot study. Therefore, an artificial elevated turbidity event, hereto referred to as a spiking study, was conducted to assess if the treatment processes being considered are capable of meeting regulatory requirements and water quality and performance goals under challenging raw water quality conditions. During the spiking study, the primary independent variable evaluated between the two pilot treatment trains was the oxidant feed point. Train 1 was configured to feed intermediate ozone, while Train 2 was configured to use pre-ozone as is shown in Figure 5-36. Two filters on each train were in service, specifically those designed for 12 gpm/sf (60 inches of 1.3 mm anthracite over 12 inches of 0.65 mm sand) and 8 gpm/sf (48 inches of 1.1 mm anthracite over 12 inches of 0.55 mm sand).

Figure 5-36. Process configuration and flow rates for the spiking study

Data are presented for three distinct phases during the spiking study. The first phase, Unmodified Raw Water, characterizes data collected before the spiking study from May 27 through June 3, and after the spiking study from June 11 through June 16. The ‘Turbidity Spiking Study, PACl Testing’ phase includes data collected during the initial turbidity spiking trial on June 3 when PACl was used for coagulation on both trains. The ‘Turbidity Spiking Study, Alum Testing’ period is the third phase, and includes data from June 10 and 11 when alum was used for coagulation on both trains to treat the spiked water.

5.7.1 Influent Water Quality

The artificial elevated turbidity event was created using soil harvested from the Bull Run watershed. The soil was specifically selected for geologic and hydrologic representativeness of what is likely to contribute to a real turbidity event. The soil was mixed with Bull Run water, then pre-settled before spiking use to represent what might happen in the supply reservoirs. The spiking solution provided a 20 NTU influent to the pilot for a duration of 30 hours, including a brief spike of up to 100 NTU. These spiking targets were selected to simulate a turbidity event that might follow a severe storm in the watershed, but are not intended to represent a catastrophic event.

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Spiking the pilot influent water raised the turbidity from around 0.3 NTU to around 20 NTU over a sustained period. Particle counts similarly increased from around 2,300 particles/mL to over 30,000 particles/mL. The size distribution of the particles shifted toward larger sizes with the majority of particles falling into the Giardia-surrogate size range (5 to 15 µm) during the spiking study; however, particles in the smaller Cryptosporidium-surrogate size range (3 to 5 µm) also increased by almost an order of magnitude during spiking. Organic indicators such as color and UV254, particularly those measuring dissolved organic material, were largely unaffected by the spiking.

Table 5-18 lists the results of grab sampling done on pilot influent water during the spiking study. Table 5-19 lists the averaged values of continuous online monitoring done on the pilot influent water. Both tables summarize influent water quality by the three phases of the spiking study.

Table 5-18. Average Grab Sample Results of Pilot Influent Water Quality Parameters During Turbidity Spiking Study Alkalinity True Operational Turbidity TSS TOC DOC Filtered SUVA (mg/L as pH -1 Color Condition (NTU) (mg/L) (mg/L) (mg/L) UV254 (cm ) (L/mg-m) CaCO3) (Pt-Co) Unmodified Raw 0.27 <0.5 8.2 7.2 0.96 0.97 0.043 4.43 6.6 Water (10) (1) (4) (10) (5) (5) (10) (5) (10) Turbidity Spiking 18.3 16 7.4 6.7 0.99 0.84 0.034 4.05 6 Study, PACl Testing (2) (1) (2) (2) (1) (1) (1) (1) (1) Turbidity Spiking 16.2 19 8.5 7.3 1.3 0.86 0.037 4.30 6 Study, Alum Testing (4) (2) (1) (2) (2) (2) (2) (2) (2) Note: Number in parentheses indicates number of samples used for average.

Table 5-19. Average Online Monitoring Results of Pilot Influent During Turbidity Spiking Study Total Particle 3-5 µm 5-15 µm Turbidity Temp. Operational Condition Counts Particle Counts Particle Counts (NTU) (°C) (particles/mL) (particles/mL) (particles/mL) Unmodified raw water a 0.30 10.4 2,560 690 600 Turbidity Spiking Study, PACl testing a 20.3 13.1 32,300 8,010 20,060 Turbidity Spiking Study, alum testing a 19.1 12.2 32,610 6,430 21,110 Turbidity Spiking Study, alum stress testing b, c 87.7 16.8 - - - Note: Data taken every 5 minutes during the operational period, with null data and repeated data removed. a. Data during this operation condition was taken from Floc/Sed 1000. b. Data from this operation condition was taken from Floc/Sed 2000. c. Particle count data from this operational condition did not record.

Background raw water turbidity was around 0.3 NTU through the spiking study. During the Turbidity Spiking Study, including both the PACl Testing and Alum Testing periods, the influent turbidity was increased to approximately 20 NTU by spiking the high-turbidity slurry into the raw water feed. The influent turbidity decreased slightly over time as the head in the spiking tank lowered and the spiking pump flow and relative fraction of spiked water decreased slowly.

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This was compensated for by regularly adjusting the spiking valve throughout the course of the spiking study, resulting in a slight saw tooth pattern.

The turbidity measured by Floc/Sed 2000 was largely consistent with that measured on Floc/Sed 1000, except delayed by the residence time through the ozone skid. This demonstrates that there was not significant settling or other turbidity reduction occurring through the ozone skid on the pre-ozone train.

Turbidity during the alum stress testing varied. Stated averages in Table 5-19 and Table 5-20 are better represented by the curves presented in Figure 5-37 and Figure 5-38.

Figure 5-37. Influent turbidity during Turbidity Spiking Study, PACl Testing

Figure 5-38. Influent turbidity during Turbidity Spiking Study, Alum Testing For approximately 40-minutes, the influent turbidity was at 100 NTU, the instrument calibrated limit.

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Particle counts in the unmodified raw water averaged around 2,500 particles/mL, with 27 percent in the 3 to 5 µm size range and 23 percent in the 5 to 15 µm size range. The spiked water during PACl and Alum testing raised the total counts by over an order of magnitude to around 32,000 particles/mL. The size distribution in the spiked water shifted such that 20 to 25 percent of particles fell in the 3 to 5 µm size range, while the fraction of particles in the 5 to 15 µm size range increased to 62 to 65 percent. Throughout the duration of the overall pilot study, the influent water typically had higher counts of the smaller size particles with the largest fraction in the 2 to 3 µm size bin, so the addition of the spiking slurry shifted the particle size distribution to a greater relative fraction of particles in the larger bin size. It is unknown what the particle size distribution would be in a naturally occurring turbidity event to know if this shift is representative. It is known that particle counts in every bin size did increase from unmodified to spiked water. Influent particle counts during the two spiking events are shown in Figure 5-39 and Figure 5-40.

Figure 5-39. Influent particle counts during Turbidity Spiking Study, PACl Testing

Figure 5-40. Influent particle counts during Turbidity Spiking Study, Alum Testing

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Influent water pH and alkalinity were largely unaffected by the spiking. Some variability was observed, but not enough samples could be taken during the limited duration study to clearly demonstrate an effect.

Water temperature was affected by spiking. Pilot influent temperature was affected by a fraction of water coming from the spiking tank, as shown by increasing 2 to 3°C during PACl and Alum testing, and increasing more than 6°C when targeting 100 NTU during the Alum stress testing period. This demonstrates that the water that had been sitting in the outdoor spiking slurry tank for up to 1 week was warmer than raw water, as expected. However, this small change over a short period was not expected to significantly affect treatment performance.

The spiked influent water contained a slightly higher TOC concentration and lower DOC concentration than unmodified influent water. Filtered UV254 absorbance and true color were largely unchanged. This suggests that any added organic matter from the spiking slurry was particulate, rather than dissolved. Again, it is unknown if material associated with natural turbidity events is dissolved or particulate.

5.7.2 Coagulation, Flocculation, and Sedimentation

During the turbidity spiking study, the flow rates in the flocculation/sedimentation skids were reduced compared to the rates tested during the rest of the pilot study. This change increased the HRT in the flocculation basins and decreased the sedimentation loading rate in the sedimentation basins. As explained in Section 5.0, the pilot had targeted approximately 30 minutes flocculation detention time and a sedimentation loading rate of 0.2 gpm/sf (23 minutes detention time with 24 inclined settling plates) during standard operations to match design parameters suggested to be likely for the full-scale facility. The flow rates used for the turbidity spiking study would result in a flocculation time of 55 minutes and a sedimentation loading rate of 0.12 gpm/sf (40 minutes detention time with 24 plates).

During the PACl Testing period, one flocculation basin was taken out of service and half of the sedimentation plates were removed from each train to compensate for the increased detention time. This resulted in two-stage flocculation with 37 minutes of detention time. By removing plates such that only 12 were remaining, the sedimentation loading rate was set to 0.2 gpm/sf. This approach was initially chosen to most closely represent scalable design targets for normal operation. It also captured the most challenging flocculation and sedimentation process configuration tested. Settled water turbidity was too high, and coagulation dosing adjustments did not lower it. So to eliminate a variable that could be limiting settling performance, the floc basins and sedimentation plates were put back into service to allow for the maximum flocculation and sedimentation time. The flocculation mixers’ velocity gradients were also adjusted in an attempt to improve flocculation. The adjustment of the flocculation detention time (including number of flocculation basins in service) and the sedimentation hydraulic loading rates (including number of inclined plates in service) did not strongly affect sedimentation performance or filterability. The rest of the turbidity spiking study was completed with the longer flocculation detention time and lower sedimentation loading rate (flocculation time of 55 minutes and a sedimentation loading rate of 0.12 gpm/sf). Consistent

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with other pilot experiments discussed, adjustments to these parameters did not have much impact on performance, and are not being used to inform full-scale design.

5.7.3 Settled Water Quality

After preliminary jar testing to determine the starting point for chemical dosing, the pilot team started the spiking at the pilot on June 3 with spiked water and PACl as the coagulant. During this period, both trains were operated to target charge neutral coagulation, starting at doses similar to jar testing. After a few hours of minimal coagulant dose changes, neither train was able to reduce settled water turbidity below 12 NTU; therefore, the pilot team decided to increase the PACl dose in order to attempt to achieve sweep floc formation. This attempt was not successful; following the increase in PACl dose, the settled water turbidity in both trains increased to the point that the settled water turbidity matched the inlet turbidity values. The inlet and settled water turbidities from this trial are shown below in Figure 5-41 for Train 1 and in Figure 5-42 for Train 2. Filter effluent quality on both trains also significantly decreased after this adjustment. Visual observation of the coagulated water following the increase in PACl indicated that conditions were not suitable for the precipitation of sufficient aluminum hydroxide to achieve sweep flocculation, while leaving the coagulated water was too positively charged to allow for floc formation via charge neutralization.

Figure 5-41. Influent and settled water turbidities for Train 1 (intermediate ozone) during the Turbidity Spiking Study, PACl Testing

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Figure 5-42. Influent and settled water turbidities for Train 2 (pre-ozone) during the Turbidity Spiking Study, PACl Testing

Given the high settled water turbidity with PACl, additional jar testing was conducted to evaluate alternate coagulation conditions. This subsequent jar testing suggested that alum, with the addition of bicarbonate to supplement alkalinity, could be fed in higher quantities and significantly reduce settled water turbidity under spiked water conditions. After jar testing, the pilot team decided to change the primary coagulant to alum and continued the turbidity spiking study with alum on June 10.

Compared to the results seen from the spiked water treated with PACl, alum was much more successful in reducing settled water turbidities. As seen in Figure 5-43 and Figure 5-44, when influent turbidity was between 15 to 20 NTU, alum coagulation was able to reduce the settled water turbidity to between 4 to 5 NTU in both trains.

Figure 5-43. Influent and settled water turbidities for Train 1 (intermediate ozone) during the Turbidity Spiking Study, Alum Testing

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Figure 5-44. Influent and settled water turbidities for Train 2 (pre-ozone) during the Turbidity Spiking Study, Alum Testing

Turbidity data were supplemented with TSS laboratory results from water samples collected during all of the operational conditions experienced by the pilot during the multiday turbidity spiking study. These TSS data are summarized in Table 5-21 and Table 5-22. TSS sample results for settled water quality ranged from 2.2 mg/L during the baseline unmodified raw water conditions to 21 mg/L during the Turbidity Spiking Study, PACl Testing conditions when coagulation was sub-optimal. During the Turbidity Spiking Study, Alum Testing, the settled water TSS decreased substantially to 4 mg/L.

Table 5-20. Train 1 (intermediate ozonation) TSS results Spiking Tank Raw Inlet Pilot Floc Basin Floc Settled Water Operational Condition (mg/L) (mg/L) (mg/L) (mg/L) Unmodified raw water, prior to spiking <0.5 3.2 2.9 Spiked water, PACl testing 77 16 21 12 Spiked water, Alum testing 20 19 4 Unmodified raw water, post-spiking 4 2.2

Table 5-21. Train 2 (pre-ozonation) TSS results Spiking Tank Raw Inlet Pilot Floc Basin Floc Settled Water Operational Condition (mg/L) (mg/L) (mg/L) (mg/L) Unmodified raw water, prior to spiking <0.5 3 2.5 Spiked water, PACl testing 77 16 21 12 Spiked water, Alum testing 20 24 5 Unmodified raw water, post-spiking 3.8 2.5

Prior to spiking, the TSS in the unmodified raw water was less than 0.5 mg/L. Following coagulation, the TSS increased to 3 to 3.2 mg/L because of the precipitated aluminum hydroxide and coagulant aid addition. Under these conditions, less than 10 percent of the TSS was removed during sedimentation in the intermediate ozone train, leaving a settled water TSS

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of 2.9 mg/L. The pre-ozone train performed slightly better, reducing TSS by approximately 17 percent from 3.0 to 2.5 mg/L.

As described above, sedimentation was not effective for turbidity removal during the Turbidity Spiking Study, PACl Testing. PACl dose ranged between 1.1 mg/L as Al3+ and 5.1 mg/L as Al3+ with 0.3 mg/L to 0.4 mg/L of C-359. However, some removal of TSS was observed in both trains. Both trains saw TSS increase by 30 percent from the raw water value of 16 mg/L to a value of 21 mg/L in the outlet from Flocculator 3. Sedimentation then reduced TSS by more than 40 percent in both trains, dropping the settled water TSS to 12 mg/L. Performance between the two trains was identical, suggesting that oxidation strategy did not significantly impact floc formation or sedimentation performance.

During Turbidity Spiking Study, Alum Testing, the settled water quality for this period was similar between both trains. Settled water TSS for both trains resulted in a TSS residual of 4 mg/L in the intermediate ozone train, and 5 mg/L in the pre-ozone train. The concentration of TSS in raw water averaged around 20 mg/L. After the addition of chemicals, the intermediate ozone train (Train 1) saw a nominal reduction the amount of TSS coming out of Flocculator 3, while the TSS coming out of Flocculator 3 in the pre-ozone train (Train 2) was approximately 4 mg/L higher than the TSS of the raw water. This suggests the pre-ozonation may have made coagulation more efficient, potentially forming more aluminum hydroxide through a ‘microflocculation’ effect. However, there was minimal difference in the settled water TSS in both trains, and both pre- and intermediate ozone removed more than 78 percent of the solids in the flocculation basin through the sedimentation process.

5.8 Solids Handling Considerations

Management of residual solids and liquid waste streams will be an important consideration for the full-scale filtration facility. While it is difficult to directly quantify solids production at pilot- scale, observations made during pilot testing can inform planning for residuals management at the full-scale Filtration Facility.

Solids production can be accurately estimated based on a stochiometric analysis of the chemicals used for treatment. Aluminum-based coagulants, such as PACl and alum, will precipitate as an amorphous (am) aluminum hydroxide [Al(OH)3∙3H2O(am)], which has a molar mass of 132 grams per mole (g/mol). Therefore, assuming the active aluminum, or Al3+, in the coagulant is fully converted to aluminum hydroxide, every 1 mg/L as Al3+ of aluminum-based coagulant will produce 4.89 mg/L of aluminum hydroxide solids. Water treatment coagulant aids and filter aids, if used, are assumed to be fully captured by the treatment process (either sedimentation or filtration) and will produce solids on a 1:1 basis. Finally, solids present in the raw water entering the treatment process are assumed to be fully captured and will also produce solid residuals on a 1:1 basis. These relationships can be used to estimate the quantity of solid residuals that will be produced at full-scale.

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Solids production estimates based on coagulation used the coagulation conditions that were in place when TSS samples were collected for analysis. Two distinct coagulation conditions were observed: 1. When PACl was used without coagulant aid, the PACl dose averaged 0.82 mg/L as Al3+ 2. When coagulant aid was used, the PACl dose averaged 0.29 mg/L as Al3+

This reduction in PACl dose was due to the addition of a coagulant aid, cationic polymer, which was fed at an average dose of 0.40 mg/L. Converting these dosages to solids production gives a range of 2.34 to 4.49 mg/L of solids produced by the chemical addition. Together with the TSS of the raw water solids, which is assumed to be 0.5 mg/L in accordance with the assumptions used in the Project Definition Report, the estimated solids production ranges from 19.5 to 37.5 lbs./MG of raw water treated.

In addition to quantifying solids production, it is important to assess where in the treatment train the solids will be collected. For most conventional surface water treatment plants, the majority of solids will settle out during the clarification process and will periodically be removed when the clarifiers are blown down. The remaining solids will carry over to the filters where they accumulate and are removed during the backwash process. It is important to distinguish between a typical water treatment plant and this source water. This differentiation is important because of the different nature of solids: clarifier blow down tends to be low in volume but relatively high in solids, while spent filter backwash water is relatively high in volume with much more dilute solids. However, unlike most conventional surface water plants, the proportion of solids captured in pilot sedimentation basins during the pilot represented a much smaller fraction of the total estimated solids production.

The proportion of solids captured in the pilot sedimentation basins was assessed in both trains by measuring the TSS in Flocculator 3, immediately upstream of the sedimentation basin, and the TSS in the settled water downstream of the sedimentation basin. The difference between these two values indicates the TSS removed during clarification. Review of these TSS data indicated a modality in the data. When PACl was fed without coagulant aid, which required coagulant doses above 0.7 mg/L as Al3+, clarification removed, on average, 25 percent of the TSS present in Flocculator 3. When coagulant aid was used, which lowered the coagulant dose below 0.5 mg/L as Al3+, the corresponding TSS removal via clarification dropped to 3 percent. Additionally, a few data pairs of TSS data were collected when alum was used as the primary coagulant. When alum was fed at a dose of 1.4 mg/L as Al3+, the average TSS removal was 51.5 percent; when the alum dose dropped to 0.73 mg/L as Al3+, the average TSS removal dropped to 40 percent. These relationships are shown graphically in Figure 5-45. The vertical distance between the gray line in the figure and each paired data point represents the corresponding TSS removal for that data pair.

Alum data shown in Figure 5-45, when the alum dose was 1.4 mg/L as Al3+, were collected during the spiking study. All other data were collected during regular operations, when raw water turbidities were low.

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Figure 5-45. Relationship between measured TSS in Third Flocculation Basin and paired Settled Water TSS

The difference between solids removal via clarification appears to be influenced by coagulation conditions, as the data groupings in indicate. Other pretreatment conditions, such as pre- oxidant (or lack thereof), did not have a clear influence on TSS removal. Therefore, the choice of coagulant and coagulant conditions will have a strong influence on both the quantity of solids produced by the full-scale treatment facility and the location(s) from which those solids are generated. If the full-scale facility operates with coagulant aid and targets charge neutralization, almost all of the solids will be expected to carry over through the sedimentation basins to the filters. Therefore, all of the ~20 lbs./MG of solids production will be collected through the spent filter backwash water. Conversely, if the facility targets a higher coagulant dose (which would substantially reduce or eliminate the coagulant aid that can be fed while still achieving charge neutralization), approximately a quarter of the solids would be retained in the sedimentation basins and discharged to residuals treatment via the sedimentation basin blowdown. Changing to a different coagulant, such as alum, would further increase the solids capture in the sedimentation basins and shift the residuals collection from spent filter backwash water to sedimentation basin blowdown. Similarly, changing to a different coagulation strategy, such as sweep flocculation, would both increase solids production and shift solids collection from spent filter backwash water to sedimentation basin blowdown.

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5.9 Coagulation, Flocculation, and Sedimentation Summary

The following bullets summarize the primary findings from this pilot study associated with coagulation, flocculation, and sedimentation. • Coagulant Testing and Selection − Following the initial period of coagulant comparison, it was apparent that under the conditions tested, alum and PACl offered better performance than had been obtained when using ferric chloride or ACH as the primary coagulant. − In general, there was no clear performance difference between alum and PACl.

 Filter productivity was slightly higher with PACl when pre-oxidation was not applied, and somewhat higher with alum when pre-oxidation was implemented (the GAC filter columns saw an increase in UFRVs, but the anthracite column did not).

 Organics removal showed an opposite trend, with an increase in TOC removal in the alum fed trains with pre-oxidation applied.

 With both coagulants, filter productivity and filter effluent particle counts met performance goals, provided that filter aid was also used. − Based on these initial results, the decision was made to use PACl as the primary coagulant during fall testing. This decision was made primarily on operational grounds; while performance was similar between both alum and PACl, alum required more careful monitoring of raw water alkalinity and required feeding supplemental alkalinity (in the form of sodium bicarbonate) at higher alum doses. Because PACl is less sensitive to alkalinity, it was easier to maintain PACl coagulation at the pilot. • Coagulation − Because of low raw water turbidity, settled water turbidity was often higher than pilot influent. Settled water turbidity was a poor indicator of coagulation performance. Other indicators used to monitor coagulation were filter water quality, filter productivity, streaming current monitor readings, and zeta potential readings. − Both the SCM and zeta potential readings provided feedback that helped optimize coagulation. The zeta potential signals tend to be more robust because it produces an absolute, not relative, quantification of zeta potential conditions and is less influenced by variation in raw water quality. • Flocculation − Over the range of HRT and mixer intensities tested, changes to flocculation did not produce observable variations in flocculation efficiency or performance. − Under the charge neutralization conditions tested (i.e., low coagulant doses that could not create a sweep floc condition), coagulation was very sensitive to chemical dosing, and small changes in coagulant and coagulant aid dosing could reduce coagulation performance.

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• Coagulant Aid − During initial trials in later summer/early fall, coagulant aid did not appear to significantly improve performance of coagulation, sedimentation, or filtration. − Starting in the winter, filter productivity began to decrease when using PACl. Adding coagulant aid was found to significantly increase filter productivity and stability under those conditions. − Use of coagulant aid and the associated reduced use of primary coagulant correlated with a slight reduction in organics removal through settling. − SDS testing conducted when coagulant aid was in use found that there were detectable levels of NDMA in filter effluent samples after 14 days of incubation. PWB plans to evaluate the source of and options to prevent and/or control NDMA in future pilot plant work. • Sedimentation − Under normal operating conditions, changes to the SLR did not produce observable variations in sedimentation efficiency or performance over the range of SLRs tested. − Settled water turbidity was often higher than raw water turbidity due to the fact that the raw water turbidity was so low to begin with and turbidity is added through coagulant addition. The settled water turbidity was anticipated to be higher than the raw water turbidity and so this performance finding was as expected. − A conventional treatment process including coagulation, flocculation, sedimentation, and filtration provided added benefit compared to direct filtration. Even though the sedimentation process does not capture the majority of solids produced at the pilot plant under normal operations, comparison of equivalent conditions between conventional treatment and direct filtration treatment found that filtration was more productive with sedimentation than with direct filtration. Under typical raw water quality conditions, both conventional treatment and direct filtration surpassed filtered water quality goals when coagulation conditions were well-controlled. • Turbidity Spiking Study − During the PACl phase of the Turbidity Spiking Study, charge neutralization coagulation produced filterable floc but was not effective in producing a settleable floc. Increasing coagulant dosage did not increase precipitation of aluminum hydroxide, and did not induce sweep floc conditions. The PACl coagulation may have had a charge unbalance or been alkalinity limited at the higher PACl doses. − A settleable floc was produced during the alum trial of the Turbidity Spiking Study with an average dose of 1.5 mg/L as Al3+ and 36 mg/L sodium bicarbonate, which resulted in a settled water pH of 7 and alkalinity of approximately 20 mg/L as CaCO3. Under these conditions, approximately 75 percent of the raw water turbidity was removed through coagulation, flocculation, and sedimentation.

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• Solids Handling Considerations − Under the range of conditions tested, estimated solids production ranged from 19.5 to 37.5 lbs./MG of raw water treated. − If PACl is used with a coagulant aid, it is expected that almost all of the solids produced will carry over to the filters and be collected via spent filter backwash water. If PACl is used without coagulant aid, it is estimated that approximately 25 percent of the solids produced will be collected via sedimentation basin blowdown (with the remainder carrying over to the filters and being collected via spent filter backwash water).

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6.0 Oxidation

Oxidant testing results including ozone and chlorine kinetics, pre-ozonation, pre-chlorination, and intermediate ozonation testing are presented in this section. Performance during each testing scenario will be presented in terms of UFRVs, turbidity, particle counts, organics removal, and DBP reduction. Specific operating conditions (dose and contact time) will be presented at the start of each results subsection. Results for oxidant demands seasonally and during turbidity spiking will also be presented. Results are presented for the ozone demand and decay to evaluate performance and inform the ozone system design. No credit for disinfection for the ozone system is requested at this time.

6.1 Ozone Kinetics

The following sections discuss ozone kinetics from bench-scale and pilot-scale testing to inform ozone dose and contact time criteria.

6.1.1 Bench-scale Testing

Bench-scale ozonation demand-decay testing was conducted on Portland Bull Run surface water by the University of Colorado (CU) and BC at CU’s Boulder SEEL Laboratory to understand ozone decay rates and ozone demand for the water source, and to help inform initial operation conditions for the ozone module. The bench-scale ozonation report is provided in Appendix E. Water samples from Portland Bull Run surface water, collected on March 1, 2019, were stored at the CU laboratory until the ozone demand-decay testing on April 2, 2019. Sample water was ozonated using the batch aqueous stock solution method described in Standard Methods for the Examination of Water and Wastewater 22nd edition 2350 D. Aqueous ozone concentrations were measured using the direct UV method at 260 nanometer (nm) wavelength and dosed at four target applied ozone doses of 0.5, 1.0, 1.5, and 2.0 mg/L. Ozone residuals were analyzed using Hach ozone reagent AccuVac ampules at multiple contact times.

Figure 6-1 shows the ozone residual over time at the different applied ozone doses, as well as the reaction rates, which decrease with increased applied dose. The difference between the applied ozone dose and ozone residual, measured at 30 seconds, was identified as the instantaneous ozone demand. On average, the instantaneous ozone demand was 0.43 mg/L as O3. In addition, ozone residual was measurable at greater than 65 minutes for higher ozone doses (1.5 and 2.0 mg/L) where there was not sufficient ozone demand.

Water quality parameters (DOC, TOC, UV200-800, and apparent color) were measured throughout the testing to evaluate the transformation of organic compounds and potential impacts on DBP precursors. Ozone did not impact TOC and DOC concentrations or pH. On the other hand, UV254 and apparent color were significantly reduced with increased ozone dose.

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Figure 6-1. Bench-scale ozone decay curves, March 2019

6.1.2 Pilot-scale Ozone Demand and Decay

An ozone residual demand and decay curve as a function of nominal detention time was

developed from ozone residual operational data when ozone was dosed at 1.0 mg/L as O3 for Trains 1 and 2 in October 2019 (Figure 6-2). A boxplot of Train 2 with a dual fit rate constant overlaid is also presented in Figure 6-3 for this data set. The nominal contact time was calculated based on a constant flow rate of 9.5 gpm and information on the geometry of the ozone contactor. It was confirmed that using the exact instantaneous flow rate signal data for computing contact time did not make a substantial difference in the outcome of this analysis due to small changes in the flowrate, so the nominal preselected constant flow rate was used for the calculation. The transferred ozone dose (calculated value based on the difference between the ozone mass applied and the ozone mass remaining in the headspace) was used for the ozone concentration at detention time zero. Train 1 has a more limited data set than Train 2. This is because during the period of data collection for ozone decay analysis, Train 1 was primarily operated without ozone to compare and contrast the effect of pre-ozonation for overall pilot-scale operations.

Because of a limitation in the ozone instrumentation precision, it was necessary to adjust the pilot-scale ozone demand and decay curves to account for the residual ozone analyzers’ baseline readings. Throughout testing, the ozone residual analyzers recorded ozone concentrations, even when ozone was not generated. These baseline readings varied through time, as well as between trains. In order to represent more accurate ozone demand and decay curves in this section, the residual measurements were adjusted (or blank corrected) for the false baseline readings. In order to make these adjustments, the average baseline reading

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during the time of sampling, unique to each train, were subtracted from all residual analyzer readings. Future ozone monitoring will add bench scale grab sample analysis to further refine the measurement and data analysis techniques.

For example, during a 3-day period when the ozone generator was turned off and no residual ozone could have been present, the Train 1 probe returned an average reading of 0.11 mg/L (10th and 90th percentile of 0.8 and 0.15 mg/L, respectively) and the Train 2 probe returned an average reading of 0.06 mg/L (10th and 90th percentile of 0.05 and 0.08 mg/L, respectively (Table 6-1). The values in Table 6-1 were used to adjust the data around this time period.

Table 6-1. Minimum Ozone Concentrations Detectable by Ozone Residual Analyzers Configuration 10th Percentile Average 90th Percentile Intermediate ozone (Train 1) 0.08 0.11 0.15 Pre-ozone (Train 2) 0.05 0.06 0.08

The ozone residual curve for the target dose of 1.0 mg/L as O3 from the bench-scale test in the section above (Figure 6-1) is similar in general shape to the pilot-scale ozone residual curves. The decay rate constant was two times greater than the initial decay observed in the bench- scale curves (for a 1 mg/L dose using a first order decay fit). This is likely due to the difference in the seasonality of the samples. The bench-scale tests were taken in March and the pilot-scale evaluation occurred during the month of October when more organics were present in the water, which consumed a greater amount of ozone.

Figure 6-2. Pilot-scale ozone decay curve for Trains 1 and 2 for an applied pre-ozone dose of 1 mg/L from October 2019 Points shown at time t=0 are the calculated ozone transfer dose, not an observed ozone residual.

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Figure 6-3. Boxplot of Train 2 ozone residual curve for pre-ozonation with an applied ozone dose of 1 mg/L from October 2019 Points shown at time t=0 are the calculated ozone transfer dose, not an observed ozone residual.

Ozone decay and decay kinetics were determined assuming using first order decay kinetics. The kinetics were compared between Trains 1 and 2 for both single and split rate constants. The rate constants were not adjusted for temperature effects. The calculated rate constants were similar for both Trains 1 and 2 curves despite the variation in the water quality. The R2 indicated a good correlation for both curve fits with slightly higher correlation for a split rate constant. These values are described in Table 6-2.

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Table 6-2. Pilot-scale Ozone Decay Kinetics for Treatment of Raw Watera Parameter Variable Train 1 Train 2 1st Order Decay (k) 0.42 0.34 Single Fit Constantb R2 0.99 0.99

High Rate (kh) 0.48 0.40

Low Rate (kl) 0.30 0.007 Dual Rate Constantc A 0.99 0.96 R2 (d) 0.99 0.99 Number of Samples -- 1,512 3,034 a. Temperatures ranged from 11 Cͦ to 15 Cͦ over the period of data collection. b. 1st Order Single Fit Constant Equation: = , where = time (min), = initial concentration (mg/L), = final concentration (mg/L), = decay constant (min-1)−. 𝑘𝑘𝑘𝑘 𝐶𝐶 𝐶𝐶0𝑒𝑒 𝑡𝑡 𝐶𝐶0 𝐶𝐶 c. 1st Order Split Rate Constant Equation: = [ + (1 ) ] , where = time (min), = initial concentration 𝑘𝑘 (mg/L), = final concentration (mg/L), and = computed−𝑘𝑘ℎ𝑡𝑡 decay constants−𝑘𝑘𝑙𝑙𝑡𝑡 (min-1), and is a dimensionless value less 0 0 than one that determines the regions of𝐶𝐶 high𝐶𝐶 and𝐴𝐴 ∗low𝑒𝑒 rates. − 𝐴𝐴 ∗ 𝑒𝑒 𝑡𝑡 𝐶𝐶 𝐶𝐶 𝑘𝑘𝑙𝑙 𝑘𝑘ℎ 𝐴𝐴 d. R2 values were evaluated using the sum of residual squares.

6.1.2.1 Ozone Contact Time Comparison Prior to May 2020, the ozone contact times were 16 minutes for the intermediate ozonation train (Train 1) and 13 minutes for the pre-ozonation train (Train 2). Starting on April 30, 2020, the ozone injection location was moved to the third dosing channel, which has the effect of minimizing the ozone contact time for the pilot equipment. The goal was to match as closely as possible the currently proposed full-scale ozone contact time of 8 minutes in both trains. For the intermediate ozone train, the ozone residual analyzer was placed in the second port of the 5th column to detect ozone residual at an ozone contact time of 8 minutes. In the pre-ozonation train, the ozone residual analyzer was in the last sample port of the 5th column for an ozone contact time of 8 minutes. Water was physically in the oxidation contact chamber for 8.0 minutes in the pre-ozone train and 9.8 minutes in the intermediate ozone train.

Ozone demand decay characteristics at the two contact time ranges are presented in this section to compare the ozone demand and decay with changing ozone contact time. Filter performance at the two contact times is presented in the context of the pre- and intermediate ozonation operations in Section 6.5, in terms of UFRVs, filter effluent turbidity, filter run time, and particle count log removals.

Throughout both the April and May study periods, ozone dose was chosen to meet demand. The ozone dose started low and increased stepwise until a residual was detected at the 8 minute contact time analyzer location, then the dose was backed off slightly to match the highest dose that demonstrated no residual. In this way the ozone demand during the longer contact time testing was found to be 0.7 mg/L for the intermediate ozone train and 0.8 mg/L for the pre- ozone train, whereas ozone demand was found to be 0.35 mg/L for the intermediate ozone train and 0.5 mg/L for the pre-ozone train during the shorter contact time testing. This was verified periodically, but largely remained unchanged through the study periods.

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Figure 6-4 and Figure 6-5 present the ozone decay curve from sampling during the longer and shorter ozone contact time periods, respectively. Figure 6-4 shows the ozone decay curve with the contact times of 16 and 13 minutes for measurements collected on April 13, 2020, while shows the ozone decay curves with the shorter contact times of 8 minutes, for measurements collected on May 5, 2020. The ozone contact time extends past these contact times because the ozone residual sample takes approximately 2.3 minutes to travel from the sample port to the analyzer through the sample tubing. For the shorter contact time testing, the decay curve shows that the ozone residual was fully consumed by the first measurable point on each train.

Both ozone decay curves were adjusted for the false baseline readings mentioned previously. These adjustments were done using the calculated average residual reading in each train during the time of sampling, while ozone generation was off. This adjustment resulted in some values, seen in Figure 6-5, dropping slightly below zero.

Figure 6-4. Ozone decay curves for intermediate ozonation (T1) and pre-ozonation (T2) with longer contact times, from April 2020

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Figure 6-5. Ozone decay curves for intermediate ozonation (T1) and pre-ozonation (T2) with shorter contact times, from May 2020

To fully understand the details of the decay curves in Figure 6-4 and Figure 6-5, it is helpful to consider five points. First, the curves are depicted as averages surrounded by 10th and 90th percentile lines to capture how the measured residual expectedly varies with time, both as a function of slightly variable influent water quality and as equipment efficiency cycles. Second, the first data point on each graph (time = 0 minutes) is an estimated total transferred ozone dose from the HMI calculated by the difference in the injected mass of ozone and measured mass of ozone in the off-gas normalized to the flow rate. The remaining data are collected from the online ozone residual analyzer. Third, each data point is delayed by 2.3 minutes compared to the point in the contact chamber it is measuring to account for the travel time in the sample tubing from the sample port to the probe. For example, the final sample port on the pre-ozone train that has 8.0 minutes of contact time in process is shown on this graph at 10.3 minutes. Fourth, the first measured point for each graph (5.5 minutes for pre-ozone and 6.3 minutes for intermediate ozone) represent the first measurement that can be taken from a sample port that is not within the same column/contact chamber as the ozone injection. Measurements from ports within the injection chamber have been found to be widely variable because ozone bubbles are still present and not fully transferred to solution.

Given that there is no difference in the residual between the two trains listed in Figure 6-5, both trains are demonstrating that there is no measurable ozone residual at the applied doses. The operational goal of the ozone dosing scheme presented in Figure 6-5 was to dose ozone to meet demand and produce a low ozone residual.

Ozone demand through the contactor (i.e., the difference between the transferred dose and the measured residual at the end of the contactor) is compared for the pilot operations shown in Figure 6-6. The data presented in Figure 6-6 are based on a moving average of 50 data points or roughly 4 hours.

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Train 2 operated in a pre-ozonated scheme from August through June. Train 1 had pre- ozonation in operation from August 20 to 30, October 2 to 11, and January 21 to March 10. Intermediate ozonation was employed in Train 2 from April 3 to June 30 with a switch to pre- ozonation for the filtration evaluation trial from May 12 to June 2.

Figure 6-6. Ozone demand throughout pilot testing, August 2, 2019-June 30, 2020 No adjustments were made on timeseries ozone decay values. When both trains were operated with pre-ozonation, the data overlay. Pre-ozonation exhibited a higher ozone demand than intermediate ozonation. From April 3 to April 29, the ozone demand in the intermediate ozonation train (Train 1) was lower than the demand observed in the train using ozone for pre- oxidation (Train 2) with an average intermediate ozone demand of 0.46 mg/L and an average pre-ozone demand of 0.60 mg/L. When the ozone contact time lowered to 8 minutes on May 1, 2020, the average demand shifted to 0.19 mg/L for intermediate and 0.39 mg/L with pre- ozonation. At both ozone contact times, the ozone demand was greater with pre-ozonation compared to intermediate ozonation. When considering the ozone demand across seasons, the ozone demand was higher during the fall when organics are highest, and the demand remained elevated through March. This calculated demand may be influenced by the operation of the ozonation process. In mid- September, the pre-ozone dose in Train 1 was increased from 0.5 mg/L to 1.0 mg/L. From mid- September to March, an ozone dose of 1.0 mg/L was typically applied and the contact time was 13 to 16 minutes. Some of the ozone demand may be attributed to ozone decay.

The pre-ozonated demand increased in June during the turbidity spiking study. The difference in ozone demand between pre-ozonation and intermediate ozonation was greatest during the turbidity spiking study, with the maximum difference of 0.94 mg/L. The pre-ozone demand presented in Figure 6-6 is lower than the peak ozone demand measured because it is a moving average calculation. Section 6.6.3 describes the findings from comparing pre-ozonation and intermediate ozonation during the turbidity spiking study.

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6.2 Chlorine Kinetics

The following sections discuss chlorine kinetics at the pilot-scale to inform chlorine dose and contact time criteria.

6.2.1 Pilot-scale Chlorine Demand and Decay

A chlorine residual demand and decay curve as a function of detention time was developed from chlorine grab-samples taken throughout the treatment process of Train 1, when chlorine was dosed at 0.3 mg/L and 1.0 mg/L as Cl2 (Figure 6-7). Figure 6-7 represents the average free chlorine residual measured from five daily samples taking when dosing 1.0 mg/L Cl2 from November 22, 2019 to December 17, 2019 and one sampling event when dosing 0.3 mg/L Cl2 on October 15, 2019.

According to the same process for ozone demand and decay described in Section 6.1.2, the nominal contact or detention time was based on the flow rate and the geometry of the contactor as well as the detention time throughout the subsequent processes. Total chlorine measurements were taken with an SL1000 handheld analyzer.

Figure 6-7. Chlorine decay curve for Train 1 when dosing at 1 mg/L and 0.3 mg/L and operating with pre- chlorination

Unlike the ozone kinetics, chlorine was present much longer throughout the processes, with low concentrations reaching the filter influent when dosing 1 mg/L as Cl2 after approximately 70 minutes of contact time. Throughout the pre-chlorination testing with a dose of 1 mg/L, an average of 0.51 mg/L as Cl2 was measured in the anthracite filter effluents. When initially dosing at 0.3 mg/L as Cl2, from October 14, 2019 to November 7, 2019, anthracite filter effluent chlorine concentrations were below the 0.03 mg/L detection limit. The chlorine concentration in Filter 4 effluent was always below the detection limit, which is expected because GAC quenches chlorine.

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6.3 Pre-ozonation and No Pre-oxidation

The first round of pre-oxidant testing compared conventional treatment without pre-oxidation in Train 1 to conventional treatment with pre-ozonation in Train 2, as shown in Figure 6-8. An applied pre-ozone dose for Train 2 was initially set at 0.5 mg/L when this round of testing began on August 30. On September 18 the applied pre-ozone dose for Train 2 was increased to 1.0 mg/L, where it was maintained for the remainder of the scenario. At the beginning of the scenario, both trains were fed PACl at a nominal dose of 0.59 mg/L as Al3+, along with 0.01 mg/L of filter aid. On September 23 the PACl dose was increased to 0.77 mg/L as Al3+ on both trains, based on SCM measurements to improve particle surface charge neutralization. The trial ended on September 30.

Figure 6-8. Treatment train for pre-ozonation treatment evaluation, August 30-September 30, 2019

6.3.1 Settled Water Quality

Settled and raw water turbidity data for both trains are presented below in Figure 6-9 to compare settled water turbidity with the presence (Train 2) or absence (Train 1) of pre- oxidation. Settled water particle count data from Train 1 are also presented to compare to settled water turbidity in Train 1. A particle counter was not on Train 2 at the floc/sed outlet, and therefore settled water particle counts are not compared between the two trains.

The data presented in Figure 6-9 are from online turbidimeters and particle counters, recording data at a 5-minute interval, along with turbidity grab sample data collected daily during the week. The settled water turbidity is also compared to the raw water turbidity grab samples in Figure 6-9. During the testing period, settled water turbidity had the potential to be influenced by the presence of pre-oxidation in Train 2. The number of plates in the sedimentation basins, and the corresponding SLR was maintained at 0.3 gpm/sf during the testing period.

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Figure 6-9. Comparison of raw and settled water turbidity and settled water particle counts in Train 1 (No Oxidant) and raw and settled water turbidity in Train 2 (Pre-ozonation), August 30-September 29, 2019 Settled water turbidity grab samples remained relatively stable under 1 NTU throughout the testing period regardless of pre-oxidation. Given that the raw water quality has such a low initial turbidity, turbidity actually increased through the flocculation/sedimentation process from the addition of coagulant chemical in both trains.

The settled water particle counts were recorded from Train 1, with no oxidation throughout this period. Particle counts in both the 3 to 5 µm and the 5 to 15 µm were fairly consistent across this timeframe, with the 3 to 5 µm particles higher than the 5 to 15 µm throughout. Because of the limitation of the particle counters installed on only one train, no data were collected for Train 2, the pre-ozonated train.

For the testing period, TOC was 0.78 mg/L on average in the raw water. TOC was reduced to 0.63 mg/L in Train 1 with no oxidant, and 0.75 mg/L in Train 2 with pre-ozonation. Overall, TOC was reduced less through sedimentation after ozonation (only 3 percent on average) compared to the train with no oxidant (19 percent). The removal through sedimentation was less of the total fraction of removal through the treatment process with ozonation compared to with no oxidant. TOC removal through sedimentation was limited because the floc did not settle very much, resulting in low levels of solids removal. However, the coagulation/flocculation process was important to improve TOC removal through filtration. See Section 6.3.2.4 for organics removal through filtration.

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6.3.2 Filtration Performance

This section describes filtration performance when testing pre-ozonation in Train 2 and no oxidation in Train 1.

6.3.2.1 Turbidity

Figure 6-10 shows the filter effluent turbidities recorded during accepted filter runs during this test period. Ozone pre-oxidation appears to have benefited the 72-inch GAC column (F3-GAC-72), whose median filter effluent turbidity was almost half that of the corresponding column with non-ozonated water (F4-GAC-72). Interestingly, this trend was not observed for the two, 72-inch anthracite columns. Instead, the non-ozonated columns (F6-Anth-72) had a lower median filter effluent turbidity and more consistently lower filter effluent turbidities than the pre-ozonated columns (F1-Anth-72). During this period, filter aid dosing was still being improved. Therefore, the result appears to be an issue of chemical dosing rather than an impact of pre-oxidant, and not a reason to conclude pre-oxidation does not generally benefit turbidity reduction. Additionally, despite these differences, the 95th percentile for all columns was below the turbidity threshold of 0.1 NTU.

Figure 6-10. Filter effluent turbidities recorded during accepted filter runs during side-by-side testing of pre- oxidation and no pre-oxidation, August 30-September 29

6.3.2.2 Particle Counts Particle counts and log removals from August 30 to September 30 are summarized in Table 6-3, including the 50th and 95th percentile raw water and filter effluent percentile particle counts and turbidities, along with average log removal data for the particle count size ranges that are surrogates for Cryptosporidium and Giardia. All of the filters demonstrated 2.0-log removal of particles in the 3 to 5 µm range. Five of the six filters also demonstrated 2.5-log removal of particles in the 5 to 15 µm range. In the GAC filter (Filter 4) that did not demonstrate a 2.5-log

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removal (close at 2.4-log removals), the particles met the goal of being less than 50 particles/mL in the 5 to 15 µm range for 95 percent of the run time. Five of six filters met this goal for both test conditions, demonstrating excellent performance during this period regardless of pretreatment. The anthracite filters at 12 gpm/sf had very low 50th percentile particle count levels in the 5 to 15 µm range, but surpassed the 95th percentile value of 50 particles/mL.

Table 6-3. Particle Counts Summary of Pre-ozonation and No Pre-oxidation, August 30-September 29 Sampling Location Raw Water Parameter 50th Percentile 95th Percentile Turbidity (NTU) 0.53 0.79 Particles 3 to 5 µm 763 1,046 (particles/mL) 5 to 15 µm 497 644 Testing Condition Train 2: Pre-ozonation Train 1: No Pre-oxidation 50th 95th Average Log 50th 95th Average Log Parameter Percentile Percentile Removala Percentile Percentile Removala Filter Configuration F1–Anth–72, 12 gpm/sf F6–Anth–72, 12 gpm/sf Turbidity (NTU) 0.05 0.10 -- 0.03 0.05 -- Particles 3 to 5 µm 1 90 2.4 5 9 2.2 (particles/mL) 5 to 15 µm 0 72 2.6 2 4 2.5 Filter Configuration F2–GAC–60, 8 gpm/sf F5–Anth–60, 8 gpm/sf Turbidity (NTU) 0.03 0.08 -- 0.01 0.04 -- Particles 3 to 5 µm 1 8 2.8 4 6 2.3 (particles/mL) 5 to 15 µm 0 12 2.6 2 3 2.5 Filter Configuration F3–GAC–72 12 gpm/sf F4–GAC–72, 12 gpm/sf

Turbidity (NTU) 0.02 0.05 -- 0.05 0.07 --

Particles 3 to 5 µm 1 37 2.6 6 10 2.1 (particles/mL) 5 to 15 µm 0 29 2.5 2 4 2.4 a. Average log removals are calculated based on averaging log removals from paired data (raw water and filter effluent for the same aliquot of water based on the HRT) when raw water particles in the indicated size range exceeded 500 particles/mL.

Particle counts during the period are provided on Figure 6-11, which shows an increase of particle counts at the end of the runs in the anthracite filters. Though Filter 1’s particle count levels are low, the 95th percentile is higher than the other filters because it is directly related to high particle counts at the end of the run, which inflate the statistic for this period. The increased particle counts towards the end of the filter run can be controlled and was not observed in later testing, as discussed below, and does not demonstrate that the target cannot be met with the testing regime. The average log removal was greater/better for the pre- ozonation train.

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Filter effluent particle counts were strongly influenced by pre-oxidation with ozone during this period. During this period, filters treating water that had been treated with a pre-oxidant were characterized by very low particle counts through the majority of the run, followed by a sharp increase of particles at the end of each run. Filters that received water that had not been treated with a pre-oxidant were found to have higher filter effluent particle counts throughout the filter run.

Therefore, the particle count statistics shown in Table 6-3 are somewhat misleading; even though the 95th percentiles from the non-ozonated filters (Filters 4 and 5) are lower than those from the filters with ozone (Filters 2 and 3), the filter effluent particle counts from the latter filters are lower through the majority of the run. Despite the higher numbers, this is the preferred performance regime, as the ends of the filter runs can more easily be managed by operators than poorly controlled particles through the entire run. It is only the breakthrough of particles at the end of the runs that inflate the statistics for the filters receiving water treated with a pre-oxidant. Subsequent testing in the following months was able to better control the ends of filter runs to prevent this breakthrough.

Figure 6-11. Comparison of particle counts with (Filter 1) and without (Filter 6) pre-ozonation, August 30- September 29, 2020

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There were additional time periods when ozonation was temporarily turned off and an increase in filter effluent particle counts was observed in November and April. Figure 6-12 shows the particle counts in April 2020. Ozonation was not in operation from April 29–30. With no other changes to the treatment processes, particles jump up in all filters with no ozonation (pre- ozonation or intermediate ozonation). There was a larger increase in particles on the intermediate train compared to the pre-ozonation train. This larger increase is due to the fact that a lower filter aid dose was applied on the intermediate train for the corresponding filter media design on the pre-ozonation train.

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Figure 6-12. Particle count data for pre-ozonation and intermediate ozonation when ozone was turned off, from April 29-30, 2020

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6.3.2.3 Filter Run Time and UFRVs The calculated UFRVs for this condition are presented in Figure 6-13. Overall, it is clear that pre- ozonation significantly improves filter productivity. For example, the ozonated anthracite filter with a filtration rate of 12 gpm/sf (F1-Anth-72) had a 50th percentile UFRV of approximately 18,000 gal/sf-run, while the no pre-oxidant anthracite filter at the same filtration rate had a 50th percentile UFRV of approximately 10,000 gal/sf-run. On average, the median UFRV for the pre-ozonated filters was 1.5 times greater than that of the no pre-oxidant filters. The UFRVs on both trains surpassed the goal of 6,500 gal/sf-run during 95 percent of the operational time. All of the filters’ UFRV 50th percentiles were at or greater than 10,000 gal/sf-run. The filters receiving water treated with ozone significantly surpassed the performance target.

Figure 6-13. Calculated UFRVs during side-by-side testing of pre-oxidation and no pre-oxidation, August 30- September 29, 2019 Figure 6-14 summarizes the run time data for all six filters in a box and whisker plot format. Generally, the filter run times were longer in the filters with pre-ozonation, correlated to higher UFRVs. Additionally, the box and whisker plot reveals there is a distinct correlation between filter run time and filtration rate where longer filter run times were observed in the filters operated at lower filtration rates. This correlation is expected given the fact that lower filtration rates should result in longer run times because less water is being passed through the filter equivalent to a filter with a higher filtration rate.

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Figure 6-14. Filter run time from pre-oxidation and no pre-oxidation, from August 30 to September 29, 2019

6.3.2.4 Organics Removal Tables 6-4 and 6-5 summarize the average organics removal from the raw to the filtered effluent to further compare organics removal during the pre-ozonation testing period. Overall, organics removal was high with and without pre-oxidant, showing that the coagulation process is a vital component. TOC was removed from an average of 0.78 mg/L to an average filtered -1 effluent of 0.39 mg/L, and filtered UV254 reduced from an average of 0.032 cm to an average of 0.005 cm-1. Color reduction was excellent with reductions from an average of 4.9 Pt-Co to below the MRL in all filters.

Table 6-4. Average TOC Removal During Pre-Ozonation and No Pre-Oxidation Testing, August 30-September 29, 2020 TOC Average Removal Test Sample Average TOC Condition Location Average Percent Removala No. of Samples Std Dev (mg/L) Raw Water 0.78 -- 12 0.05 F1-Anth-72 0.48 38% 12 0.04 Pre- F2-GAC-60 0.31 60% 12 0.05 ozonation F3-GAC-72 0.32 59% 12 0.06 F4-GAC-72 0.3 62% 12 0.1 No pre- F5-Anth-60 0.43 45% 12 0.01 oxidation F6-Anth-72 0.43 45% 12 0.01 a. Average TOC removals were determined by averaging the computed daily removal of TOC between raw and individual filter effluent.

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Table 6-5. Average Filtered UV254 Reduction During Pre-Ozonation and No Pre-Oxidation Testing, August 30-September 29, 2020

Filtered UV254 Average Reduction Test Sample Average UV254 Std Dev Condition Location Average Percent Reductiona No. of Samples (cm-1) (cm-1) Raw Water 0.032 -- 18 0.003 F1-Anth-72 0.004 89% 18 0.002 Pre-ozonation F2-GAC-60 0.002 95% 18 0.001 F3-GAC-72 0.002 94% 17 0.002 F4-GAC-72 0.005 84% 17 0.002 No pre- F5-Anth-60 0.008 75% 17 0.002 oxidation F6-Anth-72 0.008 74% 17 0.002

a. Average reduction of UV254 were determined by averaging the computed daily reduction of UV254 between raw and individual filter effluent.

Organics removal between the two trains was similar, with slightly greater reduction in UV254 in the ozonated train. There was little difference in the filter effluent TOC between the two trains, with removal between 45 to 62 percent in the train with no oxidant, and 38 to 60 percent in the pre-ozonated train. Filtered UV254 in the pre-ozonated train was lower than with no oxidant, indicating that pre-oxidation is transforming the organics present in the raw water. During this test period, filtered UV254 decreased by an average of 92 percent in the ozonated train, compared to 78 percent in the train with no pretreatment. Additionally, as expected, the GAC filters removed more TOC and UV254 compared to the anthracite filters.

6.3.3 Chlorine Demand and Decay and Disinfection By-Products

In November 2019, PWB conducted an SDS assessment to evaluate the effect of filtration and various treatment approaches on the formation of DBPs and CDD during disinfection with free chlorine and chloramines. Full details of the SDS testing approach and results are summarized in the November SDS and Disinfection Evaluation Report provided in Appendix B.

When the pilot plant was sampled for the November SDS evaluation, each train was operated in conventional treatment mode with coagulant PACl dosed at 0.9 mg/L as Al3+ and nonionic filter aid polymer dosed at 0.020 mg/L. Train 2 was pre-ozonated with a dose of 1.0 mg/L-O3 and 13 minutes of contact time prior to coagulant addition in the rapid mix tank. Train 1 was operated without a pre-oxidant. The raw water contained 0.3 NTU turbidity and 1.3 mg/L TOC and was 8.9°C. The SUVA was 4.4 L/mg-m.

Sampling for water quality analyses, including TTHMs and HAA5s, was performed at the beginning, middle, and end of the 14-day SDS period. Results for the 14-day CDD and DBP concentrations are summarized in Figure 6-15 and Figure 6-16, respectively. During the SDS testing, calcium thiosulfate was dosed at 0.25 mg/L to quench the ozone residual. Calcium thiosulfate can exert a demand on chlorine, therefore the results for the CDD in Train 2 with pre-ozonation are likely conservative, and could have been impacted by the calcium thiosulfate addition.

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Figure 6-15. SDS test results for chlorine demand and decay with pre-ozonation and no oxidant

Figure 6-16. SDS Test Results for 14-day TTHMs and HAA5s with pre-ozonation and no oxidant

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Overall, both trains showed improvement in terms of DBP concentrations in finished water compared to existing treatment during November 2019 testing. All filters were at or below 10 µg/L TTHM or HAA5s, which is less than a quarter of the MCL, and met the Bull Run Treatment Project goal to reduce DBPs to below 50 percent of the regulatory limits. Additionally, the CDD is lower in the filtered samples, compared to the Lusted Outlet and raw water. The following key observations were made between the filters for CDD and DBP concentration. • The CDD calculated during the free chlorine contact period in the pre-ozonated filtered samples was about two times that of the non-pre-oxidized filtered samples (0.6 mg/L compared to 0.3 mg/L). Some if not all of this difference is likely a result of additional demand from calcium thiosulfate, used to quench ozone. • The 14-day CDD was similar or slightly higher in pre-ozonated samples than in filtered samples that were not pre-oxidized. The difference suggests that, in comparison with the filters that are not pre-oxidized, the ozonated train filters are not removing as much of the oxidizable material and/or are converting the material to a form that is more oxidizable. • Filtration decreased the DBP levels substantially when compared to both the Lusted Outlet and raw water. In all initial filtered effluent samples, both groups of DBPs were below 10 µg/L. • DBP concentrations were low, less than 10 µg/L for both TTHMs and HAA5s, for all filtered effluent samples. DBPs were slightly lower in samples collected from the pre-ozonated filters than in samples collected from the filters without an oxidant applied, indicating there is a benefit to pre-ozonation for DBP removal. HAA5s measured after 14 days ranged between 4.4 and 5.5 µg/L in ozonated samples, and 5.2 and 7.9 µg/L in samples with no oxidant. TTHMs measured after 14 days ranged between 4.9 and 6.7 µg/L in pre-ozonated samples, and 7.9 to 9.8 µg/L in samples with no oxidant.

6.3.4 Summary

This period of testing evaluated how pre-oxidation with ozone influenced pilot plant behavior. Overall, pre-ozonation is clearly important for pretreatment in the Bull Run water. The following key observations were made based on this testing period: • Compared against the train that was not treated with pre-oxidant, pre-oxidation resulted in lower filter effluent turbidities in the GAC filters but higher filter effluent turbidity in the anthracite filters, though both anthracite and GAC filters met filter water turbidity goals. Results during this period were influenced by non-optimized filter aid dosing, which likely resulted in higher turbidity than might have been achieved. • Average particle counts from the pre-ozonated filters were lower than those from the no pre-oxidant filters. • Pre-ozonation increased filter productivity, as measured by filter UFRVs. On average, the median UFRV for the pre-ozonated filters was 1.5 times greater than that of the no pre- oxidant filters.

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• Organics removal was already notable (45 to 62 percent), and was not substantially improved by pre-ozonation. Pre-ozonation improved reduction of UV254 (an average of 92 percent in the ozonated train compared to 78 percent in the train with no pre-oxidant). TOC removal was on the order of roughly 60 percent with either scenario. • Overall, both trains showed vast improvement in terms of lower DBP concentrations in finished water compared to existing treatment, with DBPs all below 10 µg/L. CDD was also lower after filtration. DBPs were slightly lower in the pre-ozonated filters than the filters with no oxidant indicating pre-ozonation can improve DBP removal. • During the fall season of ozone testing when organics are usually highest, an applied ozone dose of 1.0 mg/L resulted in an ozone residual of less than 0.1 mg/L after an ozone contact time of approximately 14 minutes.

6.4 Pre-chlorination and No Pre-oxidation

Pre-chlorination was also investigated as a possible pre-oxidant. Figure 6-17 shows a schematic of the treatment approach. From November 18 to December 4 the pilot operated with pre- chlorination on Train 1 (Filters 4, 5, and 6) and no-oxidant on Train 2 (Filters 1, 2, and 3). During that time, there were two periods when the data were excluded; an ozone leak shut down operations from November 24 to 27, and coagulant aid was not dosed properly to Train 2 from November 27 to 29. As a result, data are presented for this testing condition from November 18 to 24 and November 29 to December 4. Chlorine was dosed at 1.0 mg/L and both trains were fed PACl at a dose of 0.77 mg/L as Al3+. Non-ionic filter aid (Clarifloc N-6310) was injected at the settled water discharge to the filters, where it was fed at a nominal dose of 0.025 mg/L in both trains.

Figure 6-17. Treatment train for pre-chlorination and no pre-oxidation, November 18-December 4, 2019

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6.4.1 Settled Water Quality

During this test period, the coagulation, flocculation, and sedimentation modules for both trains were operated in conventional treatment mode with three-stage flocculation and sedimentation. The number of plates in the sedimentation basins and the corresponding SLR was maintained at 0.3 gpm/sf during the testing period. PACl was used as the coagulant without coagulant aid and was dosed at 0.77 mg/L as Al3+ to maintain the SCM value as close to neutral as practicable.

Figure 6-18 compares the raw and settled water turbidity as well as the particle counts in Train 1, which was pre-oxidized with 1.0 mg/L chlorine dose, to Train 2 with no pre-oxidant.

Figure 6-18. Comparison of raw and settled water and settled water particle counts in Train 1 (Pre-chlorination) and raw and settled water turbidity in Train 2 (No oxidant), from November 18 to December 4, 2019 Data were excluded from November 24 -27 due to ozone leak, and from Nov 27–29 due to issue with dosing of coagulant aid to Train 2

The settled water turbidity remained relatively constant during the test period, with the settled water grab samples trending toward the high end of the online turbidimeter readings in both trains. There is an increase in turbidity through sedimentation. Turbidity removal through sedimentation appears to be largely uninfluenced by the presence of pre-chlorination.

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The settled water particle counts were recorded from Train 1, with pre-chlorination. Particle counts in both the 3 to 5 µm and the 5 to 15 µm were consistent across this timeframe, with much less variation in particle count measurements in Figure 6-18 when compared to Figure 6-17 with no pre-oxidation.

During this testing period, raw water TOC was higher on average than previous months (1.25 mg/L). TOC was reduced by 12 percent in both trains to an average of 1.10 mg/L in the settled water. Overall, there was no distinct difference in TOC removal through sedimentation between the trains with and without pre-chlorination. See Section 6.4.2.1. for organics removal through filtration.

6.4.2 Filtration Performance

Filter performance for the periods with pre-chlorination compared to no pre-oxidation is summarized in Table 6-6, including the average and 95th percentile for UFRVs, filter run times, and effluent turbidity for each filter.

Table 6-6. Summary of Filter Performance for Pre-Chlorination and No Pre-Oxidation Filter Run Time UFRV (gal/sf) Filter Effluent Turbidity (NTU) Test (hours) Filter Condition 95th No. of No. of 95th No. of Average Average Average percentile Samples Samples percentile Samples F1-Anth-72 7,634 9,300 9 12.9 9 0.04 0.09 1,305 No oxidant F2-GAC-60 6,132 8,900 6 18.6 6 0.03 0.08 1,320 F3-GAC-72 4,091 5,400 18 7.5 18 0.03 0.07 1,590 F4-GAC-72 6,178 6,800 16 9.5 16 0.04 0.06 1,811 Pre- F5-Anth-60 10,379 11,600 6 24.1 6 0.02 0.09 1,397 chlorination F6-Anth-72 5,557 7,200 14 10.0 14 0.05 0.10 1,548

Both conditions generally produced lower UFRVs than the previous testing of pre-ozonation and no pre-oxidation, likely due to the increase in pilot influent organic concentrations associated with fall seasonality. Average UFRVs ranged between 5,400 and 9,300 gpm/sf with no oxidant, and 6,800 and 11,600 gpm/sf with pre-chlorination, indicating a moderate improvement for the 72-inch GAC filters (F3-GAC-60, F4-GAC-40) with pre-chlorination. Performance was better for the 72-inch anthracite filter with no oxidant. Both lower filtration rate and shorter profile filters had better performance.

It appears that during this test period, the filter aid fed to Train 1 (pre-chlorination) was too low such that Filters 5 (F5-Anth-60) and 6 (F6-Anth-72) experienced turbidity breakthrough and backwashed because of turbidity, instead of head loss. Operation during this period made it apparent that it is necessary to add enough filter aid to minimize turbidity breakthrough and to retain the particles in the filter bed. Refer to Section 7.1 for the overall takeaways on the use and dosage approach for filter aid.

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Filter effluent turbidities were excellent with the average 95th percentile below 0.1 NTU for all filters. It appears that the pretreatment approach did not significantly impact the average turbidities, with average turbidities between 0.03 to 0.04 NTU with no oxidant and 0.02 to 0.05 NTU with pre-chlorination.

Total particle counts comparing operation with pre-chlorine and no oxidant are summarized in Figure 6-19. During this period, it is evident that pre-oxidation is an important treatment step in this water to minimize filter effluent particle counts. With pre-chlorination, the filters often produced water with total particle counts in the single digits, and even lower in the individual size ranges of interest.

Figure 6-19. Total Particle Counts Summary for Pre-Chlorination and No Pre-Oxidation, November 18-24 and November 29-December 4, 2019 6.4.2.1 Organics Removal

Table 6-7 provides a summary of the average organics removal from the raw to the filtered effluent with and without pre-chlorination. As observed during the testing period with pre- ozonation, organics removal was high with and without pre-chlorination, showing that the coagulation is an important step in the process.

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Table 6-7. Average Organics Removal During Pre-Chlorination and No Pre-Oxidation Testing, November 18-24, and November 29-December 4, 2019 -1 TOC (mg/L) Filtered UV254 (cm ) True Color (Pt-Co) Train Condition Average No. of Samplesa Average No. of Samplesa Average No. of Samplesa Influent None 1.26 5 0.052 8 9 8 Train 2 No pre-oxidation 0.48 11 0.011 24 < 3 24 Filter Effluent % Removal 61% -- 80% -- > 84%b -- Train 1 Pre-chlorination 0.57 9 0.010 21 < 3 21 Filter Effluent % Removal 55% -- 79% -- > 80%b -- a. Combined samples from all three filters in the train for the average and percent removal calculation. b. The percent removal is represented as > to indicate that the % removal is based on measurements below the MRL (3 Pt-Co).

6.4.3 Summary

Based on side-by-side testing with and without pre-chlorination, it is apparent that performance improved moderately with the use of chlorine as the oxidant. The following key observations were made based on this testing period: • Average UFRVs were between around 5,400 and 9,300 gpm/sf with no oxidant, and 6,800 and 11,600 gpm/sf with pre-chlorination, indicating a moderate improvement for the 72-inch GAC filters (F3-GAC-60, F4-GAC-40) and the 60-inch filters with pre-chlorination. • It appears that the pretreatment did not significantly impact the average turbidities, with good turbidity reduction in all filters. • Pre-oxidation is an important treatment process for this water to minimize filter effluent particle counts, with the filters producing water with total particle counts in the single digits when the oxidant is applied.

• Organics removal was high for TOC, UV254, and color with and without pre-chlorination.

6.5 Pre-chlorination and Pre-ozonation

To evaluate performance of different pre-oxidants (chlorine and ozone), the pilot was operated in a side-by-side comparison with pre-chlorination on Train 1 and pre-ozonation on Train 2, as shown in Figure 6-20. The pilot operated in this configuration initially in October for a week (October 11 through 14); however, there were issues with the ozone module that cut off the trial prematurely. The comparison started again in mid-December and operated through January 21. After January 21, Train 1 switched to pre-ozonation to test both trains with coagulant aid to try to improve filter productivity. Results demonstrating the benefit of adding coagulant aid are discussed in Section 5.4 above.

Operations from December 19, 2019 to January 21, 2020, consisted of pre-oxidant testing with 1.0 mg/L as Cl2 on Train 1 and 1.0 mg/L as O3 on Train 2. Train 1 operated with a PACl dose of 0.72 to 0.82 mg/L as Al3+, and a non-ionic filter aid dose of 0.030 to 0.051 mg/L, while Train 2 operated with a range of PACl from 0.72 to 0.90 mg/L as Al3+, and filter aid of 0.038 to

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0.053 mg/L. Non-ionic filter aid (Clarifloc N-6310) was injected at the settled water discharge to the filters.

Also during this period, the filtration rate through the 72-inch GAC filters (Filters 3 and 4) was decreased to 10 gpm/sf to mitigate high CBHL in those columns. These CBHL issues are discussed in Section 7.2.1.

Figure 6-20. Treatment train for pre-chlorination and pre-ozonation

6.5.1 Settled Water Quality

During this test period, the coagulation, flocculation, and sedimentation modules for both trains were operated in conventional treatment mode with three-stage flocculation and sedimentation. The SLR was reduced from 0.3 gpm/sf to 0.2 gpm/sf by adding additional plates to the plate settler used for sedimentation starting on December 17. Impacts of the SLR change are discussed in Section 5.5.

Figure 6-21 compares the raw and settled water turbidity, as well as the settled water particle counts in Train 1, which was pre-oxidized with 1.0 mg/L as Cl2, to Train 2 with 1.0 mg/L as O3 dose.

In general, settled water turbidity was between 1.4 and 1.75 NTU in both trains, which is about 2 to 4 times higher than the raw water turbidity. Settled water is expected to be higher than raw water as observed. Changes in settled water and raw water generally aligned during the pre-oxidation testing period for both trains. The grab samples generally trended with the online turbidimeter readings, with the exception of the raw water feed for Train 1, which shows a slight decreasing trend in the grab samples, opposite the HMI data. There was no distinct difference in settled water turbidity between Train 1 with pre-chlorination treatment and Train 2 with pre-ozonation.

Similar to the pre-chlorinated particle counts in November, shown in Figure 6-18, particle counts were very consistent within each range.

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Figure 6-21. Comparison of raw and settled water turbidity and settled water particle counts in Train 1 (Pre- chlorination) and raw and settled water turbidity in Train 2 (Pre-ozone), December 19, 2019-January 21, 2020 For the pre-chlorination and pre-ozonation side-by-side trial, the average TOC in the raw water was removed from an average of 1.20 mg/L to an average of 1.05 mg/L in the train with pre- chlorination and 1.23 mg/L in the train with pre-ozonation. TOC was reduced by 12 percent through settling with pre-chlorination compared to no removal with pre-ozonation. Overall, pre-ozonation showed less TOC removal through sedimentation than with pre-chlorination; however, the removal through the full process (after filtration) is more comparable between the oxidation schemes. See Section 6.5.2.4. for organics removal through filtration.

6.5.2 Filtration Performance

This section describes filtration performance when testing pre-chlorination in Train 1 and pre- ozonation in Train 2 in terms of turbidity, particle counts, filter run times and UFRVs, and organics removal.

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6.5.2.1 Turbidity Figure 6-22 shows the filter effluent turbidities recorded from December 19, 2019, to January 21, 2020. All of the filters produced excellent water quality for both pre-oxidation conditions. Additionally, filter effluent turbidities were generally consistent during the test period as indicated by the tight range in the box-whisker plot.

Figure 6-22. Filter effluent turbidities for pre-chlorination and pre-ozonation, December 19, 2019-January 21, 2020 6.5.2.2 Particle Counts Particle counts and log removals from the pre-chlorination and pre-ozonation comparison are summarized in Table 6-8, including the 50th and 95th percentile raw water and filter effluent percentile particle counts and turbidities, along with the average log removal data for the particle count size ranges that are surrogates for Cryptosporidium and Giardia. In general, the filters performed well with low particle counts. All filters surpassed the 2-log removal goal in the 3 to 5 µm range. Five of the six filters achieved the 2.5-log removal goal for particles in the 5 to 15 µm range. Particle counts on Filters 1 (anthracite, 12 gpm/sf, pre-ozone) and 2 (GAC, 8 gpm/sf, pre-ozone) were elevated compared to the remaining filters. Every other filter met the 95th percentile goal of having less than 50 particles/mL in the 5 to 15 µm range. The 95th percentile values for Filters 1 and 2 were influenced by ripening curves and start time for the filter run when the turbidity was below 0.1 NTU. The 50th percentile values were very low, at 1 to 2 particles/mL for all filters.

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Table 6-8. Particle Counts Summary of Pre-Chlorination and Pre-Ozonation, December 19, 2019- January 21, 2020 Sampling Location Raw Water Parameter 50th Percentile 95th Percentile Turbidity (NTU) 0.31 0.64 Particles 3 to 5 µm 878 1,063 (particles/mL) 5 to 15 µm 618 753 Testing Condition Train 2: Ozone pre-oxidation Train 1: Chlorine pre-oxidation 50th 95th Average Log 50th 95th Average Log Parameter Percentile Percentile Removala Percentile Percentile Removala Filter Configuration F1–Anth–72, 12 gpm/sf F6–Anth–72, 12 gpm/sf Turbidity (NTU) 0.02 0.09 -- 0.03 0.08 -- Particles 3 to 5 µm 1 55 2.6 1 17 2.7 (particles/mL) 5 to 15 µm 1 61 2.5 2 24 2.6 Filter Configuration F2–GAC–60, 8 gpm/sf F5–Anth–60, 8 gpm/sf Turbidity (NTU) 0.02 0.09 -- 0.02 0.07 -- Particles 3 to 5 µm 1 47 2.6 1 1 2.9 (particles/mL) 5 to 15 µm 1 58 2.3 1 1 2.8 Filter Configuration F3–GAC–72, 12 gpm/sf F4–GAC–72, 12 gpm/sf Turbidity (NTU) 0.01 0.06 -- 0.02 0.07 -- Particles 3 to 5 µm 1 2 2.8 1 11 2.7 (particles/mL) 5 to 15 µm 1 3 2.7 1 5 2.6 a. Average log removals are calculated based on averaging log removals from paired data (raw water and filter effluent for the same aliquot of water based on the HRT) when raw water particles in the indicated size range exceeded 500 particles/mL.

Particle counts in the filter effluents with pre-chlorination during this testing period were generally lower than the filter effluents with pre-ozonation. The 95th percentile particle counts for the 3 to 5 µm bin were between 1 and 24 particles/mL, while the filters with pre-ozonation were between 3 and 61 particles/mL. The results during this period had limited filter productivity, and it was clear pre-ozonation could be improved with better chemical dosing through the addition of coagulant aid. When coagulant aid was added to pre-ozonation from January 21 to Feb 3, the particle counts were more comparable to performance with pre- chlorination. For Train 1 filters with pre-ozonation and coagulant aid, the 95th percentile particle counts for the 5 to 15 µm bin ranged between 8 to 27 particles/mL, more comparable to the pre-chlorination trial.

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6.5.2.3 Filter Run Time and UFRVs The filter run times and associated calculated UFRVs for the first two operating periods are presented in Figure 6-23 and Figure 6-24,respectively. Figure 6-24 includes a horizontal dotted line at the UFRV goal of 6,500 gal/sf), and a horizontal dashed line at the higher performance goal of 10,000 gal/sf.

Figure 6-23. Filter run hours for pre-chlorination and pre-ozonation, December 19, 2019-January 21, 2020

Figure 6-24. UFRVs for pre-chlorination and pre-ozonation, December 19, 2019-January 21, 2020

During the pre-oxidant comparison, filter productivity was moderate and overall pre- chlorination and pre-ozonation had similar moderate filter performance. For both conditions, UFRVs generally ranged between the minimum target of 6,500 gal/sf and the operational goal of 10,000 gal/sf. Filters 1 and 5 had the highest UFRVs with the median in excess of

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10,000 gal/sf, and the 5th percentile at or above 6,500 gal/sf. Review of the cause of backwash during this period indicates that the majority of the filters backwashed because of head loss (based on a threshold of 12 feet) except for Filters 1 and 2, which primarily backwashed because of turbidity. Based on these results, the dosing strategy changed to test the benefit of adding coagulant aid, which proved to be beneficial (further discussed in Section 5.4).

6.5.2.4 Organics Removal

Average percent removals of TOC and average reduction of filtered UV254 from raw water to filtered effluent are summarized below in Table 6-9 and Table 6-10, respectively, for operations from December 19, 2019 to January 21, 2020, comparing pre-chlorination (Train 1) to pre- ozonation (Train 2).

Table 6-9. Average TOC Removal Through Filtration, December 19, 2019-January 21, 2020 TOC Average Removal Test Condition Sample Location Average TOC Average Percent Removala No. of Samples Std Dev (mg/L) Raw Water 1.20 -- 8 0.09 F1-Anth-72, 12 gpm/sf 0.55 54% 8 0.04 Pre-ozonation F2-GAC-60, 8 gpm/sf 0.45 63% 8 0.02 F3-GAC-72, 12 gpm/sf 0.44 63% 8 0.03 F4-GAC-72, 12 gpm/sf 0.45 63% 8 0.11 Pre-chlorination F5-Anth-60, 8 gpm/sf 0.48 60% 8 0.03 F6-Anth-72, 12 gpm/sf 0.48 60% 8 0.04 a. Average TOC removals were determined by averaging the computed daily removal of TOC between raw and individual filter effluent.

Table 6-10. Average Filtered UV254 Reduction Through Filtration, December 19, 2019-January 21, 2020

Filtered UV254 Average Reduction Test Condition Sample Location -1 a Average UV254 (cm ) Average Percent Reduction No. of Samples Std Dev Raw Water 0.056 NA 6 0.007 F1-Anth-72 0.007 88% 7 0.003 Pre-ozonation F2-GAC-60 0.006 90% 7 0.001 F3-GAC-72 0.006 91% 7 0.002 F4-GAC-72 0.007 88% 7 0.002 Pre-chlorination F5-Anth-60 0.001 82% 7 0.002 F6-Anth-72 0.009 83% 7 0.002 a. Average reduction of UV254 were determined by averaging the computed daily reduction of UV254 between raw and individual filter effluent.

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Overall, organics removal was similar for both pre-oxidants. TOC removal from raw water to filtered effluent was excellent during the pre-oxidant testing, with removals between 54 and 63 percent. There was no noticeable difference in TOC removal between pre-ozonation (Filters 1, 2, and 3) and pre-chlorination (Filters 4, 5, and 6), which was consistent with past pre- oxidant testing. In addition, the GAC filters reduced TOC slightly more than the anthracite filters. Filtered UV254 reduction appears to be insensitive to differences in filter media, pretreatment condition or chemical dosing. During the testing period, UV254 was reduced from raw to filtered effluent on average between 82 and 91 percent, reducing filtered UV254 in the raw water from an average of 0.056 cm-1 to an average of 0.007 cm-1 in the filtered effluent with minimal standard deviation in results. Color was reduced from an average of 9.2 Pt-Co to below the MRL for all seven samples, with no noticeable difference as a result of pretreatment.

6.5.3 Chlorine Demand and Decay and Disinfection By-Products

In October 2019, PWB conducted an SDS assessment to evaluate the effect of filtration and various treatment approaches on the formation of DBPs and CDD during disinfection with free chlorine and chloramines. Full details of the SDS testing approach and results are summarized in the October SDS and Disinfection Evaluation Report provided in Appendix B.

When the pilot plant was sampled for the October SDS evaluation, each train was operated in conventional treatment mode with PACl dosed at 0.90 mg/L as Al3+, and nonionic filter aid dosed at 0.010 mg/L. Train 1 was pre-chlorinated with a dose of 0.3 mg/L as Cl2 and 13 minutes

of contact time, and Train 2 was pre-ozonated with a dose of 1.0 mg/L as O3 and 13 minutes of contact time. The raw water turbidity was 0.5 NTU, TOC was 1.4 mg/L, and the temperature was 12°C.

Sampling for water quality analyses, including TTHMs and HAA5s, was performed at the beginning, middle, and end of the 14-day SDS period. Results for the 14-day CDD and DBP concentrations are summarized in Figures 6-25 and 6-26, respectively. During the SDS testing, calcium thiosulfate was dosed at 0.25 mg/L to quench the ozone residual. Calcium thiosulfate can exert a demand on chlorine, therefore the results for the CDD in Train 2 with pre-ozonation are conservative, and reflect additional demand of up to 0.25 mg/L from calcium thiosulfate.

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Figure 6-25. SDS test results for chlorine demand and decay with pre-chlorination and pre-ozonation

Figure 6-26. SDS test results for 14-day TTHMs and HAA5s with pre-chlorination and pre-ozonation

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Overall, both pre-oxidant trains showed improvement in terms of DBP concentrations in finished water compared to existing treatment during October 2019 testing, with all filters less than a quarter of the MCL. The following key observations were made between the pre- chlorinated and pre-ozonated filters for CDD and DBP concentration. • CDD measured in samples from ozonated Filters 1 and 3 was higher than in their pre- chlorinated counterparts (Filters 4 and 6, inclusive of demand exerted during the pre- chlorination; Filter 5 CDD results were not representative because of unintentional formation of dichloramine that was not stable during the 14-day incubation period). Some of this difference is likely a result of additional demand from calcium thiosulfate, used to quench ozone. The difference not attributable to the calcium thiosulfate demand, suggests that the ozonated train is producing higher levels of oxidizable material than the pre- chlorinated train, which is expected given that ozone is a stronger oxidant than chlorine. • DBP levels in all filtration treated water (Filters 1–6) were much lower than the control samples taken from the current full scale system (Lusted Outlet sample). • DBP concentrations were lower in samples collected from the pre-ozonated filters than in samples collected from the pre-chlorinated filters. HAA5s measured after 14 days ranged between 5.0 and 5.8 µg/L in ozonated samples, and 7.4 and 13.0 µg/L in pre-chlorinated samples. TTHMs measured after 14 days ranged between 8.5 and 10.4 µg/L in pre-ozonated samples, and 9.7 to 19.5 µg/L in pre-chlorinated samples.

6.5.4 Summary

Pre-chlorination and pre-ozonation showed comparable performance in terms of filterability and filter effluent water quality. The following key observations were made based on this testing period: • UFRVs were higher with pre-ozonation for the 12 gpm/sf filters than pre-chlorination. • There were no large differences in filter effluent turbidities from the two trains, with turbidities generally low (≤0.05 NTU) from all filters. • Particle counts through the majority of the filter runs with pre-chlorination and pre- ozonation were low with the 50th percentile ranging from 1 to 2 particles/mL for all filters. • Both pre-oxidation strategies produced very low DBPs (less than one-quarter of the MCL), but DBPs were lower from the pre-ozonated train. Compared to a current treatment system sample evaluated from the Lusted Hill Outlet, DBPs were reduced by 60 to 90 percent. DBP concentrations were lower with pre-ozonation.

6.6 Pre-Ozonation and Intermediate Ozonation

Side-by-side testing of intermediate ozonation and pre-ozonation started in early March, after operations stabilized with the new filter media. Operations from March 10 to March 28 involved frequent changes to chemical dosing to improve filter productivity. Through this period, the chemical dosing strategy was improved by increasing the coagulant dose and changing the filter aid dose location from the combined filter skid inlets to the individual filter

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inlets. On March 28 there was a plant shutdown, resulting in a 3 day period to troubleshoot operations upon startup. Operations starting on April 3 through May 12 were stable and were used to evaluate the side-by-side comparison of intermediate and pre-ozonation. The chemical dosing information for the testing period is summarized in Table 6-11.

The operational changes during this period were as follows: • April 3–April 28: Intermediate ozonation (Train 1) and pre-ozonation (Train 2) • April 30–May 12: Intermediate ozonation (Train 1) and pre-ozonation (Train 2) with shorter ozone contact time of 8 minutes Figure 6-27 presents the process flow configuration for the plant from April 3 to April 28, noting the change in filter aid dosing location on April 3. It also presents the configuration with the shorter contact time from April 30 to May 12. On April 29, for both Trains 1 and 2, the ozone injection location was moved from the first injection location to the third and last injection location in order to test shorter ozone contact times. Along with the change in the injection location, the ozone dose concentrations were also reduced on April 30 in order to target no residual leaving the oxidation contact chamber. Both the ozone injection location and dose adjustments were made to match the design team’s intended design of the ozonation system.

Table 6-11. Summary of Testing Scenarios for Pilot Plant Study, April 3-May 12, 2020 Test Testing Conditions

Duration Scenario Train 1 Train 2 Filter aid fed to individual filters Filter aid fed to individual filters Intermediate • Intermediate (0.7 mg/L) • Pre-ozone (0.8 mg/L) April 3– and Pre- • PACla (0.33–0.66 mg/L as Al3+) • PACla (0.39–0.42 mg/L as Al3+) April 28 ozonation • Coagulant aidb (0.28 – 0.3 mg/L) • Coagulant aidb (0.29–0.3 mg/L) • Nonionic filter aidc (0.011–0.050 mg/L) • Nonionic filter aidc (0.015–0.046 mg/L)

Intermediate Filter aid fed to individual filters Filter aid fed to individual filters and Pre- • Intermediate (0.35 mg/L) • Pre-ozone (0.5-0.55 mg/L) April 30– ozonation with • PACla (0.35–0.49 mg/L as Al3+) • PACla (0.42–0.48 mg/L as Al3+) May 12 lower ozone • Coagulant aidb (0.29 – 0.37 mg/L) • Coagulant aidb (0.3–0.37 mg/L) contact time • Nonionic filter aidc (0.012–0.022 mg/L) • Nonionic filter aidc (0.016–0.026 mg/L)

a. Coagulant = Polyaluminum Chloride (PACl) PAX-18, manufactured by Kemira, was tested as the coagulant. Dose reported as Al3+. b. Coagulant aid = Clarifloc C-359, manufactured by Polydyne, was tested as the coagulant aid. Dose reported as chemical. c. Filter aid = Nonionic polymer Clarifloc N-6310, manufactured by Polydyne, was tested as the filter aid. Dose reported as chemical.

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Figure 6-27. Pilot treatment train for intermediate ozonation and pre-ozonation evaluation, from April 3 to May 12, 2020

In contrast to testing in March, the filter aid feed locations on both Train 1 and Train 2 were moved to the individual filter heads, immediately upstream of the filter inlet pumps starting on April 3. This feed strategy allowed the filter aid feed dosing to be adjusted for each individual filter. During this test period, coagulation and flocculation on Train 1 and Train 2 were adjusted separately (i.e., there was no effort to match chemical doses between trains). On both trains, the coagulant and coagulant aid doses were adjusted based on measurements from the on-line SCM and grab sample measurements on the onsite Zeta potential.

6.6.1 Settled Water Quality

During this test period, the coagulation, flocculation, and sedimentation modules for both trains were operated in conventional treatment mode with three-stage flocculation and sedimentation, and an SLR of 0.2 gpm/sf.

Figure 6-28 compares the settled water turbidity in Train 1 with intermediate ozonation to Train 2 with pre-ozonation. Settled water turbidity between trains was similar from April 3 to April 28. Train 1 average settled water turbidity was 0.82 NTU compared to 0.78 NTU for Train 2 from April 3 to April 30. Settled water particle count data from Train 1 are also presented to compare to settled water turbidity in Train 1. A particle counter was not on Train 2 at the floc/sed outlet, and therefore settled water particle counts could not be compared between the two trains. Settled water particle counts were consistent throughout this time period. These observations are consistent with the prior month operations. The coagulant dosage was also higher in Train 2 (a difference of 0.05 mg/L as Al3+) for this reporting period.

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Figure 6-28. Comparison of raw and settled water turbidity and settled water particle counts in Train 1 (intermediate ozonation) and raw and settled water turbidity in Train 2 (pre-ozonation), April 3-May 12, 2020 From April 30 to May 12, 2020, the average TOC in the raw water was removed from an average of 0.81 mg/L to an average of 0.77 mg/L in the train with intermediate ozonation and 0.86 mg/L in the train with pre-ozonation. TOC was reduced by 5 percent with intermediate ozonation compared to no removal (-6 percent) with pre-ozonation. Overall, both ozonation schemes removed minimal TOC through sedimentation with slightly more in the intermediate ozonation train. The removal through the full process (after filtration) is more comparable between the oxidation schemes. See Section 6.6.4.1 for organics removal through filtration.

6.6.2 Clean Bed Head Loss

Figure 6-29 presents the CBHL data collected from April 3 to May 12, 2020, which was determined for a given run from the second head loss values recorded after backwashing (representing head loss after 5 to 10 minutes of operation).

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Figure 6-29. Clean bed head loss over time for filters runs, April 3-May 12, 2020 Filters 1, 2, 3 (F1, F2, F3) operated with pre-ozonation, and Filters 4,5,6 (F4, F5, F6) with no oxidant.

The filters with pre-ozonation (Filters 1, 2, and 3) had higher CBHL over time than their paired filters with intermediate ozonation (Filters 4, 5, and 6), while the CBHL data from the filters on Train 1 intermediate ozonation (Filters 4, 5, and 6) appear to be more consistent (Figure 6-29). There are two potential explanations for the observed difference in CBHL trends between the two trains. The first hypothesis is that the difference in CBHL is attributable to the difference between the microbiome downstream of pre-ozone oxidation (Train 2) and intermediate ozonation (Train 1). Alternatively, the increase in CBHL could be attributable to Train 2 having slightly higher filter aid doses than Train 1 (see Section 7.1), although the filter aid doses on both trains decreased over the duration of the test period.

6.6.3 Impact of Ozone Contact Time Variation

As described above in Section 6.1.2.1, the ozone injection location was adjusted to evaluate performance at a shorter contact time (8.0 minutes, 0.35–0.55 mg/L initial dose) to be more representative of the proposed full-scale design, and evaluate the impact to the pilot’s performance goals and whether they could still be achieved compared to performance with a longer contact time (13–16 minutes, 0.7–0.8 mg/L initial dose).

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For each train, UFRV, filter run time, filter effluent turbidity, and particle count log removals were compared with the longer ozone contact time (April 3–29), and with the shorter ozone contact time (April 30–May 12). The following key observations were made, with the overall conclusion that lowering the contact time did not compromise filter performance: • Overall, the UFRVs for both the 8- and 13-minute contact times for the pre-ozonation train and 8- and 16-minute contact times for the intermediate ozonation train were comparable, indicating that a shorter ozone contact time does not compromise performance. UFRVs surpassed the performance goal of 10,000 gal/sf for all filter runs at the shorter contact time of 8 minutes. • The effluent turbidity at the shorter contact time for both trains was low with the 95th percentiles for all filters well below the 0.1 NTU turbidity threshold (below 0.025 NTU). • For all filters, the average log removal was above the target of 2.0-log removal for 3 to 5 µm (Cryptosporidium surrogate) and 2.5-log removal for 5 to 15 µm (Giardia surrogate). A slightly higher particle count log removal was seen with the longer contact time for intermediate ozonation. The particle count log removals were comparable for pre- ozonation between the two ozone contact times. • The average filter effluent TOC concentrations were comparable at the two different ozone contact times. • Shortening the ozone contact time did not impact color removal. Excellent color reduction was observed (to non-detect levels).

6.6.4 Turbidity Spiking Study

The turbidity spiking event compared performance of pre-ozonation and intermediate ozonation. Train 1 was operated in the intermediate ozone scheme and Train 2 in pre- ozonation. Ozone was injected into the third contact chamber to target an ozone contact time of 8 minutes in each treatment train and the ozone residual analyzer was either measured at the end of the contactor (Train 2–pre-ozonation) or the time that corresponded to 8 minutes (Train 1–intermediate ozonation). The general approach towards ozone dosing was to try to dose enough ozone to match ozone demand. Additional details on the experimental approach and test results are described in the Bull Run Treatment Pilot Spiking Study TM in Attachment E. Influent water quality characteristics during the turbidity spiking study are also described in Section 5.7 of this Report.

Table 6-12 shows the estimated ozone demands during the turbidity spiking trials. Similar to what was experienced with prior testing, pre-ozonation had a higher ozone demand than intermediate ozonation. The distinction with the turbidity spiking study was that the difference in ozone demand between the two processes was greater, which is reflective of the higher turbidity creating additional ozone demand in pre-ozonation that was reduced with flocculation and sedimentation for intermediate ozonation.

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Table 6-12. Estimated Ozone Demands

Raw Water Ozone Demand (mg/L) Turbidity Spiking Study Condition Turbidity (NTU) Pre-ozonation (Train 2) Intermediate Ozonation (Train 1) PACl and coagulant aid 20 > 1.0 0.8 Alum as coagulant 20 > 1.2 0.3 Stress testing, alum as coagulant 100 > 2.3 --

Figure 6-30 presents ozone applied dose and ozone residual concentrations during the initial spiking study when PACl and coagulant aid were dosed on June 3, 2020. When 20 NTU influent water was first injected into the filtration pilot with PACl as the primary coagulant, the ozone doses on Trains 1 and 2 were gradually increased. The ozone residual rose above non- detectable levels in the intermediate ozone train as the ozone applied dose was increased above 0.8 mg/L. At a peak intermediate ozone dose of 1.05 mg/L, the ozone residual concentration measured 0.25 mg/L. For the pre-ozonation train, the ozone dose was also increased to 1.05 mg/L, but the ozone residual concentration never increased from the non- detectable levels, thus indicating that the required pre-ozone dose to meet ozone demands was greater than 1.0 mg/L. Additionally, when ozone was not being dosed, the ozone residual analyzer did not read 0 mg/L during this time. The background ozone analyzer levels are described in Section 6.1.2.1.

Figure 6-30. Ozone applied dose and ozone residual concentration during the spiking study when dosing PACl and coagulant aid with T1 (intermediate) and T2 (pre-ozone)

The spiking study was paused to explore different approaches to improve settled water quality and achieve a lower settled water turbidity. The primary coagulant was switched from PACl to alum because alum was found to produce a lower settled water quality for treating the spiking solution.

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Figure 6-31 presents the applied ozone doses and ozone residual concentrations with alum when raw water turbidity was 20 NTU, and then spiked up to 100 NTU. The applied ozone dose in Train 2 was increased as the spiking solution was added and raw water turbidity reached 20 NTU. The applied ozone dose was increased to 1.2 mg/L and the ozone residual was still not detectable. Thus, it was likely that there was additional ozone demand. Higher removal of particulates and organics was achieved through sedimentation when dosing with alum as compared to PACl, which decreased the ozone demand in the intermediate ozonation scheme on Train 1. A slight decrease in the ozone dose from 0.30 to 0.25 mg/L led to the ozone residual dropping to nondetectable levels, indicating an ozone demand of 0.3 mg/L.

Figure 6-31. Applied ozone doses and ozone residual concentrations during spiking study when dosing alum with T1 (intermediate) and T2 (pre-ozone)

A short duration stress test was completed during the turbidity spiking study where the raw water turbidity was increased to 100 NTU. Intermediate ozonation (Train 1) was turned off to lengthen the amount of time for this stress test and allow the pilot operations staff to focus on the ozone dose for a single train given the short duration of the test. The pre-ozonation dose was gradually increased from 0.55 mg/L to as high as 2.3 mg/L. As anticipated, a higher ozone demand was seen during the 100 NTU condition of at least 2.3 mg/L.

6.6.4.1 Ozone Decay Figures 6-32 and 6-33 present the ozone decay curves that highlight ozone demand and decay prior to adding the spiking solution and during the turbidity spiking study when alum was the coagulant. To develop the ozone decay curves, ozone residual was measured after the third contact chamber because ozone residual is highly variable in the contactor where ozone is being injected. Online ozone residual analyzer sample tubing was moved through the fourth and fifth contact chambers. The ozone decay curves show how the transferred ozone dose (time=0 minutes) is consumed throughout the contact time. There are 2.3 minutes of contact time in the tubing from the ozone residual sample location to the analyzer.

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Prior to the turbidity spiking solution being dosed, both the intermediate ozonation (Train 1) and pre-ozonation (Train 2) had an applied ozone dose of 0.55 mg/L (Figure 6-32). Raw water turbidity was 0.3 NTU. The intermediate ozonation train had a higher ozone residual at a contact time of 10 minutes, indicating that the intermediate train had less ozone demand. Intermediate ozonation (Train 1) required 10 additional minutes to consume the full 0.55 mg/L applied ozone dose. Therefore, pre-ozonation caused a more rapid exertion of the same ozone demand as intermediate ozonation, likely caused by a lack of coagulation, flocculation, or sedimentation of organics.

Figure 6-32. Ozone decay curves for intermediate oxidation (Train 1) and pre-oxidation (Train 2) from un-spiked period in June 2020

The initial ozone demand curve generated during spiking (Figure 6-33) corresponds to 0.25 and 1.2 mg/L applied ozone doses, chosen to offset ozone demands, on Trains 1 and 2, respectively. Both trains remained in the same intermediate and pre-oxidation configurations as during the baseline period; however, 20 NTU influent water entered the filtration pilot. Intermediate and pre-ozone both showed rapid exertions of ozone demand at these doses. Each reached nondetectable ozone concentrations within 10 minutes of contact time, with the pre-ozone train taking a higher ozone dose. The intermediate ozonation train (Train 1) on the other hand had a lower ozone demand due to organics removal in the flocculation and sedimentation modules prior to ozonation. For example, 25 percent of UV254 was removed through flocculation and sedimentation and approximately 75 percent color was removed, to below detection limit, in Train 1.

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Figure 6-33. Ozone decay curves for intermediate ozonation (Train 1) and pre-oxidation (Train 2) from turbidity spiking with alum on June 11, 2020

6.6.5 Filtration Performance

This section describes filtration performance when testing Intermediate ozonation in Train 1 and pre-ozonation in Train 2 in terms of turbidity, particle counts, filter run times and UFRVs, and organics removal.

6.6.5.1 Turbidity Figure 6-34 summarizes the effluent filter turbidity for all six filters comparing performance with intermediate ozonation compared to pre-ozonation. Overall, effluent turbidity was generally well below the 0.1 NTU goal for all filters during this testing period. This low effluent turbidity is reflected in the fact that no backwashes were triggered by turbidity during the analysis period. This shows a high degree of confidence in chemical doses during the April test period.

Figure 6-34. Filter turbidity, April 3-May 12, 2020

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Coagulation conditions resulted in an easily filterable floc and the filter aid dose was selected for and fed individually to each filter. Because of this, the filters generally maintained excellent filter effluent quality throughout their runs, until the developed head loss triggered the filter backwash.

The turbidity performance was well below the goal for both operational conditions. The 95th percentile turbidities for all filters were near or below 0.025 NTU, with a slightly higher 95th percentile for Filter 2 than the other filters as a result of a short period of inconsistent filter aid dosing.

6.6.5.2 Particle counts Figure 6-35 below presents the total particle counts during the intermediate and pre-ozonation trial from April 3 to May 12. The performance in both treatment trains was excellent, with total particle counts below 50 particles/mL, which indicates all filters met the goal of having less than 50 particles/mL in the 5 to 15 µm range. Overall, the median of filter effluent particle counts was slightly higher on Train 2 (pre-ozonation) than Train 1 (intermediate), even though the filter aid doses were slightly higher on Train 2 (Figure 6-35). During this period, Filter 2 had a 4-day period of inconsistent filter aid dosing because of air locking of the pump, resulting in a few hours of elevated particle counts. While the period with higher counts related to the air locking issue were excluded, there were still higher total particle counts in Filter 2 before and after the issue. As a result, the total particle counts for Filter 2 is slightly higher than the other filters.

Figure 6-35. Total particle counts from all filters during the intermediate and pre-ozonation trial, April 3-May 12, 2020 With excellent and consistent filter operations during this test period, individual filter runs had low particle counts and effluent turbidity. Two representative runs during this period are shown in Figure 6-36 to show there was minor differences between the trains and both filters had excellent performance. Both the example runs for Filter 2 (F2-Anth-66) and Filter 5 (F2-Anth-

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66), which operated at 10 gpm/sf extended past 20-hours and terminated on head loss without any particle count or turbidity break through.

Figure 6-36. Filter run examples for pre-ozonation and intermediate ozonation

6.6.5.3 Filter Run Time and UFRVs Figure 6-37 summarizes the filter productivity, as represented by UFRV, for each filter during the test period. There appears to be little consistent difference in filter productivity between filters receiving intermediate ozone and pre-ozone. Filters 3 and 4 had the lowest UFRVs, suggesting that for these test conditions operating the filters at higher filtration rates reduces overall productivity. This is more apparent for Filter 3 than for Filter 4 because of the period during which filter aid dose was still being adjusted at the beginning of the test period. Filters 1 and 6, which have the lowest filtration rate, had the highest UFRVs and most consistent performance. Regardless of minor differences between filters, the filtration UFRV data for this period can be considered excellent for all conditions as the median value for each filter is well above the goal of 10,000 gal/sf. The 5th percentiles for 5 out of 6 filters surpassed 10,000 gal/sf.

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Figure 6-37. Filter UFRV, April-May 12, 2020 Figure 6-38 summarizes the run time data for all six filters in a box and whisker plot format. The box and whisker plot reveals there is a distinct correlation between filter run time and filtration rate. This correlation is expected given the fact that lower filtration rates should result in longer run times because less water is being passed through the filter equivalent to a filter with a higher filtration rate. This correlation can be observed partly because filter performance was excellent for all filters, so filter run time was directly related to the rate at which the filters accumulated head loss.

Both intermediate and pre-ozonation effectively allowed for filter runs on average between 20 to 45 hours depending on the filtration rate that resulted in UFRVs that met the goal, as discussed above.

Figure 6-38. Filter Run time, April 3-May 12, 2020

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6.6.5.4 Organics Removal

Average percent removals of TOC and average reduction of filtered UV254 from raw water to filtered effluent are summarized below in Table 6-13 and Table 6-14, respectively, for operations from April 3 to May 12, 2020, comparing intermediate ozonation (Train 1) to pre- ozonation (Train 2).

The raw water TOC concentration ranged from 0.76 mg/L to 0.86 mg/L, with an average concentration of 0.80 mg/L. TOC was reduced to an average concentration of between 0.49 to 0.50 mg/L in Train 1 (intermediate ozonation) and 0.44 mg/L in Train 2 (pre-ozonation), with an average TOC removal between 38 to 39 percent and 45 to 46 percent, respectively. For all comparable filters between the trains, the average TOC was lower with pre-ozonation, and TOC reduction was consistently slightly better. While this may be partially attributable to the placement of the ozone in the process (before coagulation as opposed to post-settling), it is likely also associated with the higher PACl dose used on Train 2 for the majority of the testing period, typically higher than the Train 1 dose by about 0.05 mg/L as Al3+.

Table 6-13. Average TOC Removal Through Filtration, April 3–May 12, 2020

Test Sampling TOC Average Removal Condition Location Average TOC (mg/L) Average Percent Removala No. of Samples Std Dev Raw Water 0.80 NA 10 0.04 F1-Anth-60 0.44 46% 10 0.03 Pre-ozonation F2-Anth-66 0.44 46% 10 0.02 F3-Anth-72 0.44 45% 10 0.02 F4-Anth-72 0.50 38% 10 0.02 Intermediate F5-Anth-66 0.49 39% 10 0.03 Ozonation F6-Anth-60 0.49 39% 10 0.02 a. Average TOC removals were determined by averaging the computed daily removal of TOC between raw and individual filter effluent.

Table 6-14. Average Filtered UV254 Reduction Through Filtration, April 3-May 12, 2020

Filtered UV254 Average Reduction Test Sampling Average UV254 Condition Location Average Percent Reductiona No. of Samples Std Dev (cm-1) Raw Water 0.032 NA 15 0.009 F1-Anth-60 0.004 77% 15 0.001 Pre-ozonation F2-Anth-66 0.004 72% 15 0.002 F3-Anth-72 0.003 79% 15 0.002 F4-Anth-72 0.005 75% 15 0.001 Intermediate F5-Anth-66 0.005 73% 15 0.002 Ozonation F6-Anth-60 0.005 75% 15 0.002

a. Average reduction of UV254 were determined by averaging the computed daily reduction of UV254 between raw and individual filter effluent.

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During the testing period, reduction in UV254 was excellent with a reduction from raw to filtered effluent from an average of 0.032 cm-1 to an average between 0.003 to 0.005 cm-1 in the filtered effluent, with minimal standard deviation in results. Filtered UV254 in the filtered effluent was slightly lower in the filters with pre-ozonation, with a reduction from raw water on average between 72 to 79 percent, compared to 73 to 75 percent in the filters with intermediate ozonation. Color was reduced for both trains from an average of 4.7 Pt-Co to below the MRL of 3.0 Pt-Co.

While there were slight differences noted between the two trains (TOC < 0.06 mg/L and UV254 <0.002 cm-1), overall, the differences were not distinct. Therefore, during this testing period, there were no distinct differences in organics removal between trains based on the ozonation strategy (intermediate ozonation versus pre-ozonation).

6.6.6 Chlorine Demand and Decay and Disinfection By-Products

In April, PWB conducted additional SDS testing to compare DBP formation, free chlorine demand, and chloramine stability/decay when operating with intermediate ozonation versus pre-ozonation. Full details of the SDS testing set-up and results are summarized in the April SDS and Disinfection Evaluation Report provided in Appendix B.

When the pilot plant was sampled for the April SDS evaluation on April 22, 2020, each train was operated in conventional treatment mode using PACl as the coagulant, cationic coagulant aid (Clarifloc C-359, a polyamine), and nonionic filter aid (Clarifloc N-6310, a polyacrylamide). During the test, the PACl and coagulant aid doses fed to Train 1 were 0.36 mg/L as Al3+ and 0.3 mg/L, respectively, while the PACl and coagulant aid doses fed to Train 2 were 0.42 mg/L as Al3+ and 0.3 mg/L, respectively. Filter aid was dosed to individual filters with 0.015 mg/L to Filter 1, 0.025 mg/L to Filter 3, and 0.021 mg/L to Filter 4. Train 2 was pre-ozonated with a dose of 0.8 mg/L as O3 and 13.6 minutes of contact time prior to coagulant addition in the rapid mix tank. Train 1 was operated with intermediate ozonation using an ozone dose of 0.7 mg/L and 16.3 minutes contact time. The raw water contained 0.3 NTU turbidity and 0.8 mg/L TOC. Pilot raw water contained 0.3 NTU turbidity and 0.77 mg/L TOC. Turbidity was 0.02 NTU and total particle counts were <10/mL in all filtered samples.

6.6.6.1 Chlorine Demand and Decay Results for CDD over the course of the 60-minute free chlorine contact period and subsequent 14-day SDS incubation period are shown in Figure 6-39. Overall, both intermediate and pre- ozonation showed improvement in terms of lower CDD compared to existing treatment during the April 2020 testing. The following key observations were made between the intermediate and pre-ozonated filters for CDD: • Free chlorine demand during the 60-minute free chlorine contact period was 0.3 mg/L in filter effluent from all three filters tested, compared with 0.6 mg/L in the raw water and 0.5 mg/L in the Train 1 filter influent. Thus, the chlorine demand was reduced 20 percent through pretreatment, and 50 percent by the entire treatment process.

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• Total chlorine demand-decay was comparable between intermediate ozonation filter (Filter 4) measured to be about 0.3 mg/L compared to 0.2 mg/L for the pre-ozonated filters (Filters 1 and 3). • During the spring season, conventional treatment significantly reduces chlorine demand and decay, and pre-ozonation was slightly better than intermediate ozonation in reducing chlorine demand. (47 and 45 percent lower for Filters 1 and 3, respectively, compared to 32 percent lower for Filter 4).

Figure 6-39. SDS test results for chlorine demand and decay

6.6.6.2 Disinfection By-Products TTHMs and HAA5s were analyzed in samples collected 10 minutes following post-treatment as well as at the end of the 14-day SDS incubation period. Results for post-treatment and 14-day HAA5 and TTHM concentrations are shown in Figure 6-40 and Figure 6-41 respectively.

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Figure 6-40. HAA5 results at the beginning and end of the 14-day SDS period

Figure 6-41. TTHM results at beginning and end of the 14-day SDS period

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Overall, both intermediate and pre-ozonation showed improvement in terms of DBP concentrations in finished water compared to raw water adjusted using the same post- treatment targets during the April 2020 testing, with all filter effluents less than the MCL. The following key observations were made between the intermediate and pre-ozonated filters for DBP concentration: • Pre-treatment accounts for between 40 percent and 60 percent of the DBP reductions from the filter influent compared to raw water (TTHMs reduced by 65 percent post-treatment and 59 percent after 14 days, and HAA5s reduced by 56 percent post-treatment and 38 percent after 14 days). • TTHM and HAA5 concentrations were reduced to very low levels (<4 µg/L) in all post- treated filter effluent samples measured at the beginning and end of the 14-day SDS period, with no distinct difference between trains. HAA5s measured after 14 days were 3.2 µg/L in pre-ozonated samples and 3.6 µg/L in the sample with intermediate ozonation. TTHMs measured after 14 days ranged between 2.4 to 2.5 µg/L in pre-ozonated samples, and were 2.6 µg/L in the sample with intermediate ozonation. • The DBP concentrations were similar in filter effluent samples from both treatment trains, indicating that both pre-ozonation and intermediate ozone are highly effective at removing precursors of TTHMs and HAA5s. The pre-ozone train filters had slightly lower DBP concentrations. • DBPs with pre-ozonation or intermediate ozonation were consistently 90 percent less than in raw water both right after treatment and after the 14-day period. • Comparing the filter effluent DBP concentrations of the 14-day SDS samples to the historical May Stage 2 levels indicates that TTHM and HAA5 concentrations could be reduced greater than 90 percent from present levels using conventional treatment with either intermediate ozonation or pre-ozonation.

6.6.7 Summary

Intermediate ozonation and pre-ozonation showed comparable performance in terms of filterability and filter effluent water quality. The main differences were in terms of the ozone demand and filtered water characteristics. The following key observations were made based on this testing period: • Settled water turbidity was comparable between the intermediate and pre-ozone trains. In contrast to the filtration process, which showed strong benefits to having an upstream oxidant, the settling performance was largely the same with or without upstream ozone for the tested coagulation approach. The pre-ozonated train required a slightly higher coagulant demand than intermediate ozonation, as a result of dosing the coagulant after the ozonation process which transformed the organic material into a form with a greater ozone demand. • The filters with pre-ozonation (Filters 1, 2, and 3) had higher CBHL over time than their paired filters with intermediate ozonation (Filters 4, 5, and 6). Additionally, CBHL data from the filters on Train 1 intermediate ozonation (Filters 4, 5, and 6) appear to be more

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consistent. A definitive reason for the higher CBHL in the pre-ozone filters was not possible with the data collected, but is thought to either be a result of the ozonation strategy, or having slightly higher filter aid doses on Train 2 than Train 1 (see Section 7.1). • At both ozone contact times, the ozone demand was greater with pre-ozonation; 0.46 mg/L intermediate ozone demand and 0.6 mg/L pre-ozone demand for 13 to 16 minutes contact time, and 0.19 mg/L for intermediate and 0.39 mg/L for pre-ozonation at 8 minutes of contact time. • Lowering the ozone contact time from 13 to 16 minutes down to 8 minutes did not compromise filter performance. • Turbidity spiking: − Pre-ozonation had a greater ozone demand and the difference in demand between the two ozonation processes increased with increased turbidity. − The ozone demand for pre-ozonation was greater than 1.0 mg/L when treating 20 NTU water and greater than 2.3 mg/L when treating 100 NTU water. While ozone demand was greater in the pre-ozonated train, similar filter effluent quality and DBP reduction could potentially be achieved when operated at an ozone dose less than the observed demand. • Filter performance: − Both trains produced similar excellent low turbidity below the PSW criterion of 0.1 NTU. The 95th percentile turbidities for all filters were near or below 0.025 NTU, with no consistent difference based on the ozonation scheme. − Both trains had particle counts that were well below the project goal of 50 counts per milliliter through the filter runs. Overall, particle counts were slightly higher on Train 2 (pre-ozonation) than Train 1 (intermediate). − There appears to be little consistent difference in filter productivity between filters receiving intermediate ozone and pre-ozone. − There were slight differences noted between the two trains for organics control (TOC < -1 0.06 mg/L and UV254 <0.002 cm ), with lower TOC and UV254 in the pre-ozone train. Overall, the differences were not distinct. • CDD and DBPs: − Free chlorine demand decreased by 50 percent with intermediate and pre-ozonation compared to raw water during April sampling. − DBPs from filter effluents with pre-ozonation were slightly lower than with intermediate ozonation. In both trains, DBPs were consistently at least 90 percent less than the already low levels compared to post-treated unfiltered raw water, both right after treatment and at the end of the 14-day incubation period. − During the spring season, filtration significantly reduced CDD, with the greatest benefit occurring during the free chlorine contact period. Pre-ozonation may be more effective at removing chlorine demand (47 and 45 percent lower for Filters 1 and 3, respectively, compared to 32 percent lower for Filter 4).

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6.7 Oxidation Testing Summary

Oxidant testing results comparing pre-ozonation, pre-chlorination, and intermediate ozonation showed that oxidation is important to meet the performance goals for the future filtration facility. General observations comparing pre-oxidants and the oxidation mode are summarized as follows:

Pre-oxidation and No oxidation. Overall, pre-oxidation is important for pretreatment in the Bull Run water because of the improvements in filter productivity and reduction of filter effluent particle counts. • In general, pre-ozone appears to provide better filter productivity, and higher reduction of th UV254 than operation with no-oxidant. On average, the 50 percentile UFRVs with pre- ozonation were 1.5 times greater than the filters with no pre-oxidant. Pre-ozonation improved reduction of UV254 (an average of 92 percent in the ozonated train compared to 78 percent in the train with no pre-oxidant), indicating that pre-oxidation is transforming the organics present in the raw water. • Based on side-by-side testing with and without pre-chlorination, it is apparent that performance in terms of UFRVs and turbidity improved moderately with the use of chlorine as the oxidant. • DBPs were slightly lower in the pre-ozonated filters than the filters with no oxidant indicating pre-ozonation can improve DBP removal.

Pre-ozonation and Pre-chlorination. Both pre-ozonation and pre-chlorination were effective pretreatment methods, with few measurable differences. The few notable differences from the side-by-side comparison of pre-chlorination and pre-ozonation were as follows: • Particle counts in the filter effluent from the train with pre-chlorination were slightly lower than those from the train with pre-ozonation. As with the previous trials, the higher filter effluent counts were attributable to particles associated with breakthrough at the end of filter runs; particle counts through the majority of the filter runs were generally low. • Both pre-oxidation strategies produced very low DBPs (less than one-quarter of the MCL), but DBP concentrations were lower from the pre-ozonated train. During the pre-oxidant comparison, filter productivity was moderate, and overall pre- chlorination and pre-ozonation had similar moderate filter performance. • All of the filters produced excellent water quality for both pre-oxidation conditions. • For both conditions, UFRVs generally ranged between the minimum target of 6,500 gal/sf and the operational goal of 10,000 gal/sf. Review of the cause of backwash during the side- by-side comparison indicated that the majority of the filters backwashed because of head loss (based on a threshold of 12 feet). Based on these results, the dosing strategy changed to test the benefit of adding coagulant aid, which proved to be beneficial. • Overall, organics removal was excellent for both pre-oxidants, with no distinct differences.

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Intermediate ozonation and Pre-ozonation. Overall performance with intermediate and pre- ozonation were comparable, providing effective treatment in both ozonation modes. The main differences were in terms of the ozone demand and settled water characteristics. Performance compared between the two ozonation modes as follows: • Settled water turbidity was comparable. • Bromate samples measurements in filter effluent from both trains were non-detect. • Pre-ozonation exhibited a higher ozone demand compared to intermediate ozonation during typical operating conditions, and the difference in demand between the two ozonation processes increased with increased turbidity during the spiking study. On average, intermediate ozone demand ranged between 0.2 and 0.5 mg/L and pre-ozonation demand ranged between about 0.4 and 0.6 mg/L. • Overall, the UFRVs for both the 8- and 13-minute contact times for the pre-ozonation train and 8- and 16-minute contact times for the intermediate ozonation train were comparable, indicating that a shorter ozone contact time does not compromise performance. • The filters with pre-ozonation (Filters 1, 2, and 3) had higher CBHL over time than their paired filters with intermediate ozonation (Filters 4, 5, and 6). • Both ozonation modes produced low filter effluent particle levels achieving the water quality goals for particle counts and log removals. • Average TOC removal was about 5 percent higher with pre-ozonation. While measurable, the differences in organics removal were minor between trains based on the ozonation strategy (intermediate ozonation versus pre-ozonation). • During the spring season, filtration significantly reduced chlorine demand and decay, with the greatest benefit occurring during the free chlorine contact period, and pre-ozonation was slightly more effective at removing chlorine demand (47 and 45 percent lower for Filters 1 and 3, respectively, compared to 32 percent lower for Filter 4). • Comparing the filter effluent DBP concentrations of the 14-day SDS samples to the historical May Stage 2 levels indicates that TTHM and HAA5 concentrations could be reduced greater than 90 percent from present levels using conventional treatment with either intermediate ozonation or pre-ozonation. Pre-ozone showed slightly lower DBP formation. Intermediate and pre-ozonation both showed comparable performance with high filter productivity values. Regardless of minor differences between filters, the filtration UFRV data for this period can be considered excellent for all conditions as the median value for each filter was well above the goal of 10,000 gal/sf.

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7.0 Filtration

This section presents a summary of filter performance as it relates to the primary independent filtration variables tested throughout the pilot study: filter aid usage, filter media type, and filtration rate. Results will be presented across testing regimes, where applicable, to show overall trends from the study.

7.1 Filter Aid

Through the duration of pilot testing, filter aid proved essential in meeting filter effluent water quality goals for turbidity and particle counts. With seasonal changes in raw water, operational variations, as well as chemical dosing adjustments, filter aid proved instrumental in all instances. Limited trials performed without filter aid indicated that it was possible to achieve moderately lengthy filter runs without the use of filter aid, as shown in Figure 5-15, in Section 5.0. However, as Figure 5-15 indicates, filter performance was highly inconsistent when filter aid was not used and some very short filter runs were observed due to premature turbidity breakthrough.

Another example of the importance of filter aid is shown in Figure 7-1, which presents time series data for filter effluent turbidity and particle counts from Filter 6, a 60-inch deep anthracite filter operating at 8 gpm/sf. During the period shown, Train 1 was operating with pre-ozonation, PACl coagulant, coagulant aid, and filter aid. On May 23 the filter aid feed stopped because of air-locking, which caused an immediate increase in filter effluent turbidity and particle counts. This operational problem inadvertently provided a clear example of the influence that filter aid has in effectively retaining particles within the filters.

Figure 7-1. Turbidity and particle counts for Filter 6 example run when filter aid was removed

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Overall, the treated Bull Run water proved to be very sensitive to filter aid dosages. Although a certain amount of filter aid is necessary to minimize turbidity breakthrough and to retain the particles in the filter bed, the rate at which head loss accumulates in the filters increases proportionally with filter aid usage. Too much filter aid can prematurely shorten runs, as was observed during the November-December-January testing period along with subsequent testing in March. Average filter aid dosages for each season are summarized for both trains in Table 7-1.

Table 7-1. Average (Minimuma–Maximum) Filter Aid Doses per Season for Train 1 and Train 2 Spring Average Summer Average Filter Fall Average Winter Average Train Filter Aid Dose (mg/L) Aid Dose (mg/L) Filter Aid Dose (mg/L) Filter Aid Dose 1 0.020 (0.010–0.070) 0.018 (0.010–0.03) 0.028 (0.010–0.051) 0.029 (0.0045–0.048) 2 0.021 (0.010–0.050) 0.020 (0.01–0.05) 0.019 (0.010–0.045) 0.038 (0.019–0.056) Minimum doses are based on non-zero doses used per season

Because of operational limitations associated with the turndown on the chemical dosing pumps used to feed filter aid, prior to April 2020, filter aid was dosed at the floc/sed effluent in each train. Therefore, a common filter aid dose was shared among the filters on each train and filter aid dosing could not be tailored to the requirements of each individual filter. This, in turn, limited the extent to which filter operations could be optimized.

If particles are retained effectively in the filter and filter effluent turbidities are well-controlled, the factor limiting the length of filter runs is head loss accumulation. Throughout this pilot study, the terminal head loss threshold for triggering a backwash was 12 feet, i.e., when the total filter head loss exceeded 12 feet, a backwash would be triggered. Therefore, there are two relevant parameters that determine the length of time before a filter must be backwashed due to head loss: CBHL and head loss accumulation rate. CBHL is influenced both by the physical configuration of the filter underdrain, the inherent head loss associated with flow through the granular filter media, and any fouling head loss accumulation or particle retention that is not removed during backwashing. Head loss accumulation rate is influenced by clogging of the filter media void spaces (space between filter media particles) by flocs of particles and treatment chemicals retained in the filters (including filter aid), as well as fouling associated with biogrowth or adsorption of metals. This proved challenging when filter aid dosages were shared between the filters on a given treatment train. Because each filter had different CBHL, filters with higher CBHL (and, thus, less head loss that could be accumulated prior to reaching terminal head loss) would backwash after very short filter runs.

An example of this challenge was observed toward the end of 2019. During the latter half of November and most of December, the filter aid fed to Train 1 was low enough that Filters 5 and 6 experienced turbidity breakthrough and backwashed due to turbidity, instead of head loss. However, because of the high CBHL in Filter 4, the dose was at the high end of what Filter 4 could accommodate. Essentially, increasing the filter aid to the range that would optimize Filters 5 and 6 would cause extremely short filter runs in Filter 4. It was apparent that using a combined filter aid dose for all filters on a train would limit performance of some filters. The combined dose appeared to be lower than what was needed for the filters with the highest

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filtration rates but increasing filter aid would have reduced the run time on the lower rate filters.

In late March/early April, operational adjustments and improvements to dosing equipment were made to be able to dose filter aid to individual filters. This allowed for filter aid dosages to be optimized based on the individual filter’s CBHL, filtration rate, effluent turbidity, and particle counts, and more consistent operations.

7.2 Filter Media Type Comparison

One of the primary goals of the pilot study was to evaluate filter media configurations, including comparison of filter media types. The pilot design used for the first 8 months included 72-inch- deep GAC and anthracite filters on both trains operated at 12 gpm/sf (Filters 1 and 3 on Train 2, and Filters 4 and 6 on Train 1). These filters allowed for direct side-by-side comparison of GAC and anthracite under the operating conditions on either train. Similarly, each train had one 60-inch-deep column of different filter media types operated at 8 gpm/sf; the 60-inch-deep filter on Train 1 was anthracite (Filter 5), while the 60-inch-deep filter on Train 2 was GAC (Filter 2). These two filters (Filters 2 and 5) were intended to compare media depth to other filters within the same train. Therefore, filter media comparisons typically were restricted to comparing the performance between the 72-inch-deep GAC and anthracite filters on the same train.

The following section compares anthracite and GAC filters from three operating periods during the first 6 months of pilot plant operations. Important performance factors are compared in this section including CBHL, turbidity, particle counts, UFRVs, organics removal, biological monitoring, and DBP removal. This media comparison provided performance data to support the transition to all anthracite filters and discontinue the use of GAC media in February 2020.

Filter performance was compared between media types during three selected operating periods when operations were known to have been stable. These periods, summarized in Table 7-2, represent intervals when operations were relatively free of mechanical or process issues. During all three operating periods, the pilot plant was operated in conventional filtration mode, with flocculation/sedimentation followed by filtration. Pretreatment was varied during the operating periods to test pre-ozonation and pre-chlorination. For this section, only paired filters for each train will be considered. Data from the lower profile (60-inch total media depth) GAC and anthracite filters (Filter 2 and Filter 5, respectively) could not be directly compared because they were on different trains and not exposed to the same pretreatment conditions. However, data from those filters are presented in Appendix F, which evaluates the impact of filtration rate on both GAC and anthracite media during the first 7 months of the study.

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Table 7-2. Test Duration and Pretreatment Conditions for Filter Media Type Comparison Pretreatment Condition Train 1 (Filters 4 and 6) Test Durations Train 2 (Filters 1 and 3) Test Durations August 30–October 18, 2019 Pre-ozonation August 20–30, 2019 November 1–14, 2019 December 4–December 17, 2019 October 14–18, 2019 November 1–7, 2019 Pre-chlorinationa NA November 18–24, 2019 November 27–December 17, 2019 August 30–September 29, 2019 November 14–24, 2019 No oxidant November 14–18, 2019 November 27–December 4, 2019 Train 2 did not operate with pre-chlorination

The filtration rate was constant at 12 gpm/sf for all of the test durations shown above. Filters 2 and 5 were not included in this comparison due to differences in pretreatment conditions that made it difficult to differentiate between performance differences associated with media type and performance differences attributable to different pretreatment conditions.

It should be noted that the period of data included in this analysis aligns with those presented in Sections 5.0 and 6.0 for specific test conditions. This includes operations in November and early December, when equipment issues with the ozone and dechlorination systems prevented both trains from operating under consistent oxidation conditions for multiple weeks at a time. These changing conditions, as well as source water changes, made it difficult to consistently optimize pretreatment during this period. This was further complicated by the challenge in optimizing filter aid for all three filters on a given train, as discussed in Section 7.1.

7.2.1 Clean Bed Head Loss

As discussed previously, CBHL varied between filters. Figure 7-2 presents the observed CBHL for each filter run on the 72-inch filters between July 26, 2019, when the filtration rate was increased on each filter to 12 gpm/sf, through February 3, 2020, when the original filters’ media were removed and replaced with different filter media profiles. As Figure 7-2 shows, the CBHL on all filters increased over time; however, the rate of CBHL increase on the GAC filters exceeded that of the anthracite filters. Similarly, the Train 1 filters (Filters 1 and 3) tended to have higher CBHL than the Train 2 filters (Filters 4 and 6). The implications of high CBHL are discussed above. On December 19, in an effort to mitigate the high CBHL observed for the GAC filters, the filtration rates of Filters 3 and 4 were decreased from 12 gpm/sf to 10 gpm/sf. This did serve to restore CBHL to values similar to those for the anthracite filters (Filters 1 and 6) that were maintained at 12 gpm/sf.

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Figure 7-2. Clean bed head loss throughout the testing period for acceptable filter runs for Filters 1, 2, 4, and 6, July 26, 2019-February 3, 2020 Filtration rate on F3-GAC-72 and F4-GAC-72 decreased from 12 gpm/sf to 10 gpm/sf on December 17, corresponding to the apparent drop in CBHL on that date

Note that all filters exhibited an increase in CBHL during this period, with the two GAC filters (Filters 3 and 4) increasing at a faster rate than the anthracite filters (Filters 1 and 6). A particularly sharp increase in CBHL in the GAC filters was observed at the end of November, following a 3-day shutdown between November 24 and 27. The sharp increase in CBHL was reversed over the following weeks with increased backwash flow rates. Testing around this period suggested that some level of reversible fouling was occurring in the GAC filters. For example, back-to-back backwashes of Filter 3 at increased backwash rates on November 5 was found to temporarily decrease CBHL in Filter 3 by approximately 0.7 feet. This suggests that some of the increase in CBHL could be associated with a temporary foulant that persisted between normal backwashes, such as excess filter aid polymer and/or excess biogrowth. However, this improvement did not address the underlying issue; although the increased backwash rates lowered CBHL in the subsequent run, the average CBHL over the following 10 runs did not improve over the preceding ten runs. Therefore, while increasing the filter backwash rates did result in some short-term improvement, that change was not sufficient to reverse the observed increase in CBHL over time.

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Given the unacceptable clean bed head loss in the GAC filters (~6 feet) and the associated poor productivity of the 72” GAC filters, it was decided to reduce the filter loading rate from 12 gpm/sf to 10 gpm/sf on December 17 to match the CBHL range of the anthracite filters (4.5 to 5 feet) and increase UFRVs.

During the CBHL evaluations, it was apparent that filter underdrain losses could have a strong influence on the CBHL observed for each filter. The rebuild of the filters with new media profiles in February 2020 provided an opportunity for direct observation of the filter underdrain losses. After the original filter media were removed, and prior to placing the new media, each filter was operated at its target filtration rate using clean water. Because no media were present, the observed head losses during these empty bed trials was directly attributable to filter underdrain losses and associated structural losses (e.g., wall effects).

Table 7-3 summarizes the average observed CBHL in each column prior to the media change and underdrain cleaning from January 30 through February 3, 2020, with an average raw water temperature of 6.7 degrees C. Along with the observed CBHL for this period, the theoretical CBHL due to media friction based on the water temperature, filtration rate, and media specifications (i.e., effective size and uniformity coefficient of the sand and GAC or anthracite) are summarized, as well as unaccounted for head loss. The unaccounted for head loss may be due to biological activity, underdrain fouling, or particles in the media not being removed because of insufficient backwashes. For further detail with regards to CBHL, refer to Appendix G.

Table 7-3. Clean Bed Head Loss for All Filters, January 30-February 3, 2020 Filtration Observed Empty Observed Estimated CBHL Theoretical Unaccounted for Head Filter Rate Bed Underdrain CBHL Without Underdrain CBHLb Loss (gpm/sf) Head Loss (ft)a (ft) (ft) (ft) (ft) F1-Anth-72 12 1.20 5.98 4.78 3.70 1.08 F2-GAC-60 8 0.51 4.26 3.75 2.46 1.29 F3-GAC-72 10 0.74 6.08 5.34 3.49 1.85 F4-GAC-72 10 0.51 5.28 4.77 3.49 1.28 F5-Anth-60 8 0.04 2.46 2.42 2.40 0.02 F6-Anth-72 12 0.85 4.82 3.97 3.70 0.27

a. Losses shown collected prior to underdrain chlorine soak. See Section 7.2.1.1 for additional detail. b. Theoretical CBHL calculations did not consider underdrain losses

7.2.1.1 Underdrain Fouling CBHL When the media were removed and the filters rebuilt in February 2020, pressure measurements were collected from the empty columns before and after soaking in chlorinated water to understand how underdrain fouling may have contributed to the observed increase in CBHL over time. Theoretical head loss data were not provided by the pilot filter column manufacturer. Prior to this evaluation, head loss through the filter underdrains was thought to be nominal.

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Table 7-4 summarizes the average decrease in empty column operating head across all of the sample locations for each filter. CBHL measurements were taken at the filtration rate at which each column had previously operated, as indicated.

Table 7-4. Observed Decrease in CBHL Following Chlorine Soak Flow Rate CBHL Prior to Soak CBHL After Soak Average Decrease in CBHL Filter (gpm/sf) (ft) (ft) (ft) 1 12 1.20 0.74 0.46 2 8 0.51 0.16 0.35 3 10 0.74 0.39 0.35 4 10 0.51 0.28 0.23 5 8 0.04 0.04 0.00 6 12 0.85 0.62 0.23

In general, recovery of head loss following the chlorine soak is thought to be associated with oxidizable material being removed from the underdrain. All of the GAC filters (Filters 2, 3, and 4), as well as one anthracite filter (Filter 1), saw CBHL decrease after the chlorine soak. However, the 60-inch depth anthracite filter (Filter 5) appeared to have CBHL increase following the chlorine soak. There was no observed change in the 72-inch depth anthracite filter (Filter 6). This is because Filters 5 and 6 had been continuously chlorinated for a lengthy period prior to the media changeout and underdrain testing.

Remaining head loss that is not accounted for through the theoretical estimate of clean filter media head loss or observed underdrain head loss may be attributable to biological growth in the media, particles in the media not adequately removed in backwashing, or clogging from adhered media.

7.2.2 Turbidity

Figure 7-3 shows the filter effluent runs’ turbidities recorded during accepted filter runs conducted during the three testing periods, defined by pretreatment. In both pre-ozonation and pre-chlorinated periods, GAC filters produced lower filter effluent turbidities; however, when no oxidant was present, filter effluent turbidities were comparable for GAC and anthracite media. While GAC filters had lower filter effluent turbidities, CBHL was higher, leading to lower productivity. In all testing scenarios there does not appear to be a clear benefit of one filter media type over the other on filter effluent turbidity because all filters tested met the filter effluent turbidity goals, and observed differences in filter effluent turbidities were minimal. Turbidities in all filters were below the goal of 0.1 NTU.

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Figure 7-3. Filter effluent turbidities recorded during three operating periods: Pre-Ozone, Pre-Chlorine, and No oxidant, August 20-December 17

7.2.3 Particle Counts

Particle counts from the two media types are summarized in Table 7-5, based on pretreatment conditions. In general, the filters performed well when a pre-oxidant was present in both GAC and anthracite media, achieving greater than 2-log removal for particles in the 3 to 5 µm size range.

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Table 7-5. Particle Counts Summary, Averaged by Media Type, August 20-December 17, 2019 Sampling Location Raw Water Parameter 50th Percentile 95th Percentile Turbidity (NTU) 0.43 0.91

Particles 3 to 5 µm 682 986 (particles/mL) 5 to 15 µm 563 769 Filter Configuration GAC–72, 12 gpm/sf Anth–72, 12 gpm/sf 50th 95th Average Log 50th 95th Average Log Parameter Percentile Percentile Removala Percentile Percentile Removala Testing Condition Pre-ozonation Turbidity (NTU) 0.03 0.08 -- 0.04 0.09 --

Particles 3 to 5 µm 1 65 2.5 1 106 2.2 (particles/mL) 5 to 15 µm 1 44 2.4 1 83 2.2 Testing Condition Pre-chlorination Turbidity (NTU) 0.03 0.07 -- 0.05 0.09 --

Particles 3 to 5 µm 1 49 2.6 1 57 2.4 (particles/mL) 5 to 15 µm 1 49 2.6 1 69 2.4 Testing Condition No oxidant Turbidity (NTU) 0.03 0.07 -- 0.03 0.05 --

Particles 3 to 5 µm 20 115 1.6 6 27 2.0 (particles/mL) 5 to 15 µm 5 78 2.0 2 8 2.3 a. Average log removals are calculated based on averaging log removals from paired data (raw water and filter effluent for the same aliquot of water based on the HRT) when raw water particles in the indicated size range exceeded 500 particles/mL

The large difference between the 50th and 95th percentiles for these data is notable, particularly because this difference was not as large during some of the prior testing as presented in Sections 5.1.2.5 and 6.3.2.2. Insight into the cause of this differential can be found when reviewing individual filter runs, particularly those conducted during November and early December, such as the runs presented in Figure 7-4.

Due to operational considerations discussed above, particularly those involving filter aid dosing, many of the filter runs conducted during this period exhibited a regular pattern similar to that shown in Figure 7-4; uniformly low filter effluent particle counts throughout the majority of the run, followed by a sharp increase in filter effluent particle counts ahead of increases in filter effluent turbidity. These increases in particle counts at the end of the filter runs result in the higher 95th percentile values shown in Table 7-5.

A few higher-than-normal runs particularly skew the data set presented in Table 7-5; if one were to average the 95th percentiles from each filter run instead of taking the 95th percentile of the aggregated data set (similar to the procedure presented previously in the Interim Pilot Study Report), four of the six conditions presented in Table 7-5 would have average 95th percentile particle counts below the 50 particles/mL criterion listed in Table 1-1 for the 3 to

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5 µm range and five of the six conditions presented in Table 7-5 would have average 95th percentile particle counts below the 50 particles/mL criterion for the 5 to 15 µm range.

Following observations discussed in Section 6.0, filter effluent particle counts were higher when no oxidant was applied. This was particularly notable in the GAC filters, but also apparent in the higher-than-normal 50th percentile particle counts in the anthracite filters. Both pre-zonation and pre-chlorination were beneficial in reducing particle counts for the majority of the filter runs.

Figure 7-4. Filter run example for anthracite and GAC media with pre-ozonation

During both the pre-ozone and pre-chlorine periods, GAC and anthracite performed similarly with respect to log removal. During no oxidant testing, the log removals were lower than with pre- oxidation, with anthracite filters having a slightly higher log removal when compared to GAC.

7.2.4 UFRVs

Figure 7-5 presents the calculated UFRVs from each of the runs corresponding to the filter effluent turbidities presented in Figure 7-3, above. These figures compare filters with different media types, but the same depth and filtration rate in each train: Filters 1 and 3 for Train 2, and Filters 4 and 6 for Train 1.

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Figure 7-5. Comparison of calculated UFRVs by media type during three operating periods: Pre-Ozone, Pre-Chlorine, and No Oxidant, August 20-December 17

In general, the anthracite filters were more productive than the GAC filters, based on the pilot plant study observations presented. This is likely attributable to the higher CBHL in the GAC filters, as discussed previously. Note that the results from testing pre-chlorination were limited to the 72-inch deep filters. The 60-inch deep GAC filter (F5-GAC-60) showed the improvement with pre-chlorination over no-oxidant, as discussed in Section 6.4, above. Therefore, this presentation is limited by the data presented and does not indicate that pre-chlorination was not effective compared to no-oxidant.

7.2.5 Filter Efficiency

The pilot study had set a goal that the FTW would be less than 5 percent of the filter production or the filters would have a 95 percent efficiency for 95 percent of the operational time; however, this goal was not the primary driver for operational decisions (i.e., the pilot was not operated to optimize compliance with this goal). Instead, FTW efficiency was monitored for tracking and analysis and was not used to differentiate between processes or filter media profiles.

Figure 7-6 presents filter efficiency or the percentage of the FTW cycle of the overall filter production. The triangle on the box-whisker plot represents the 95th percentiles. If the FTW was recorded as zero minutes in the HMI because the FTW time was less than 5 minutes, 5 minutes was used for this assessment to be conservative.

All of the filters had 95th percentile efficiencies greater than 90 percent, meaning that the FTW cycle represented less than 10 percent of production. The majority of all filter run efficiencies surpassed the goal. The filters with no oxidant had the highest efficiencies. A few of the

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anthracite filters had 95th percentile efficiencies that were below 95 percent. For the pre- ozonated anthracite filter (12 gpm/sf), six of the 74 filter runs had a FTW that was greater than 5 percent of filter production or had an efficiency less than 95 percent. The pre-chlorinated anthracite filter (12 gpm/sf) had four out of 57 filter runs that did not achieve an efficiency of 95 percent. Three of the four filter runs were consecutive. However, the majority of filter runs for both pre-ozone and pre-chlorine had FTW that lasted less than 15 minutes. Given the nature of piloting, there were a few days when the operation could have been improved, but overall, the production was still good. The average filter efficiency was 97 percent and 98 percent, respectively, for the pre-ozone and pre-chlorine anthracite filters. These percentiles would likely be higher if a FTW recorded as 0 minutes in the HMI was not adjusted to 5 minutes.

Figure 7-6. Comparison of filter efficiency by filter media type

7.2.6 Organics Removal

Average removals for TOC and UV254 from the raw water to filtered effluent are presented in Table 7-6 and Table 7-7 for the three pretreatment conditions. The GAC filters (Filters 3 and 4) removed similar levels of TOC and UV254 across pre-chlorination and no oxidant treatment schemes. During pre-ozonation testing, GAC filters removed approximately 15 percent more TOC and UV254 compared to anthracite filters. During all three pretreatment conditions, all filters (GAC and anthracite) reduced color from an average of 6.4 Pt-Co in the raw water to below the MRL (3 Pt-Co).

Organics removal is also influenced by potential adsorption of organic compounds by the GAC, because virgin GAC was used for the pilot. Over time, as the media became exhausted and adsorption sites were occupied, biological activity became the primary mechanism through which organics were removed through in the GAC filter media. This transition was largely completed around December 2019, as indicated by a stabilization of relative TOC removal in the GAC filters. Even after that time the GAC filters still had a larger TOC percent removal.

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Table 7-6. Average TOC Removal by Media Type and Pretreatment Condition, August 20-December 17, 2019 Pretreatment TOC Average Removal Filter Media Condition Average TOC (mg/L) Average Percent Removala No. of Samples Std Dev Raw Water 1.03 NA 45 0.24 GAC 0.37 62% 33 0.12 Pre-ozonation Anthracite 0.51 45% 33 0.07 Pre- GAC 0.48 60% 12 0.05 chlorination Anthracite 0.57 52% 12 0.05 GAC 0.38 62% 30 0.1 No oxidant Anthracite 0.49 50% 31 0.06 a. Average TOC removals were determined by averaging the computed daily removal of TOC between raw and individual filter effluent.

Table 7-7. Average Reduction of UV254 by Media Type and Pretreatment Condition, August 20-December 17, 2019 Pretreatment UV254 Average Reduction Filter Media -1 a Condition Average UV254 (cm ) Average Percent Reduction No. of Samples Std Dev Raw Water 0.041 NA 70 0.012 GAC 0.004 88% 48 0.005 Pre-ozonation Anthracite 0.006 84% 48 0.006 Pre- GAC 0.013 77% 16 0.012 chlorination Anthracite 0.017 62% 16 0.021 GAC 0.007 84% 49 0.008 No oxidant Anthracite 0.009 76% 50 0.004

a. Average reduction of UV254 were determined by averaging the computed daily reduction of UV254 between raw and individual filter effluent.

While the raw water organics levels are very low when compared to other water supplies and therefore regulatory TOC removal requirements would not be applicable, the findings support improved organics removal by GAC media compared with anthracite media.

7.2.7 Metals and Inorganics

The inorganic constituents of interest, based on the water source and treatment chemicals used, were aluminum, iron, and manganese. This section presents the concentrations of these constituents in the filter effluent through the filter media comparison period, August 20 through December 17, 2019.

Figures 7-7 and 7-8 present concentration of total aluminum measured in the anthracite and GAC filter effluent, respectively. During this period, raw water concentrations of aluminum ranged between 9 µg/L and 27 µg/L, with the highest concentrations in the month of December. Therefore, aluminum levels in the filtered water were generally higher than the raw, with median concentrations of 21.1 µg/L and 17.7 µg/L for the anthracite and GAC filters, respectively. This added aluminum comes from the coagulant used, PACl.

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Figure 7-7. Total aluminum in anthracite filter effluent, August 20-December 17, 2019

Figure 7-8. Total aluminum in GAC filter effluent, August 20-December 17, 2019

USEPA has not established an MCL for aluminum, although a secondary MCL (SMCL) range from 50 to 200 µg/L has been established for aesthetic reasons. USEPA established a range, instead of a single SMCL, in recognition that some systems will have difficulty meeting 50 µg/L level. The total aluminum levels measured in the effluent of both the GAC and anthracite filters were relatively consistently below 50 µg/L, with several exceptions in one or more filters that are considerably higher than 50 µg/L (although no exceedances of 200 µg/L were observed). These irregular exceedances are characteristic of particulate breakthrough, suggesting that small flocs containing aluminum hydroxide were periodically present in the filter effluent. In the full-scale Filtration Facility, finished water aluminum levels should be controlled by limiting particle breakthrough through the filters.

Total iron in anthracite and GAC filter effluent are shown below in Figures 7-9 and 7-10, respectively. While iron concentrations had increased in the raw water through fall (described in Section 3.7), filter effluent concentrations were consistently below the detection limit of 5 µg/L (presented as half the MRL), in all filters. The only detection of iron in filter effluent above detection limits occurred in the effluent from Filters 1 and Filter 3 on October 2, 2019; however, these detections were well below the iron SMCL of 300 µg/L.

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Figure 7-9. Total iron in anthracite filter effluent, August 20–December 17, 2019

Figure 7-10. Total iron in GAC filter effluent, August 20–December 17, 2019

Total manganese concentrations in the anthracite and GAC filter effluents are shown in Figures 7-11 and 7-12, respectively. While the filter effluent manganese concentrations varied, they were generally below the raw water manganese concentrations during this period, which ranged from 3.5 and 14 µg/L with the highest concentrations in late September, early October 2019. Filter effluent manganese concentrations were significantly below the manganese SMCL of 50 µg/L.

Figure 7-11. Total manganese in anthracite filter effluent, August 20–December 17, 2019

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Figure 7-12. Total manganese in GAC filter effluent, August 20–December 17, 2019

For all inorganic constituents evaluated, there were no apparent differences in removal between the two filter media types.

7.2.8 Biological Monitoring

Biologically active filtration (i.e., biofiltration) at a drinking water treatment facility is an operational practice of managing, maintaining, and promoting biological activity on granular media in the filter to enhance the removal of organic and inorganic constituents before treated water is introduced into the distribution system. Naturally occurring biomass can accumulate when there is minimal to no chlorine residual in the filter influent. In biological filtration of most surface waters, aerobic respiration occurs and reduces organic compounds. Aerobic biofilters contain primarily heterotrophic bacteria, which use organic compounds as a substrate for growth (electron donor) and DO is consumed as an electron acceptor. Ozonation enhances biological filtration by creating a supersaturated DO condition and breaking down organic compounds to more readily biodegradable substrates.

Biological monitoring during the pilot study consisted of the following standard monitoring techniques including ATP, carboxylic acids, and AOC to assess the amount of biomass and biological activity in the two pilot treatment trains.

The following section presents the biological monitoring results from the testing period prior to the media change, to observe the general differences in biological growth and activity between the two media types. Overall, for the media comparison, biological monitoring demonstrated more biomass and biological activity in the GAC media filters compared to the anthracite filters. One hypothesis is that the higher CBHL and the higher organics removal observed in the GAC filters is in part associated with the higher biological activity in the GAC filters.

7.2.8.1 Media ATP ATP is a bioenergy molecule used in all living cells for energy transfer. The amount of ATP in a sample provides is a semi-quantitative means to assess the amount of biomass in a system. ATP analysis was conducted using commercially available test kits from LuminUltra. Media ATP was monitored in the first sample port at the top of the filter media bed (approximately a 6-inch depth from the top of media). The Media ATP samples were collected at different times during a filter run, which could explain some of the variation in the data. For example, not all samples

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were collected from freshly backwashed filter media. Evaluation of ATP variation during a backwash cycle or throughout a filter run was not evaluated as part of this study. The ATP filter media sampling results from four sampling events between December 2019 and February 2020, prior to the media change out, are presented in Figure 7-13. The measurements were based on dry media and adjusted for the water content. The percent water content of the wet samples varied considerably between samples, with an average water content of 50 percent for GAC samples and 20 percent for anthracite samples. Across the sampling periods, dry adjusted media ATP measured from below 20,000 picograms (pg) of ATP/g of dry filter media, to a high of 180,000 pg ATP/g. The samples from December 18 and January 15 were influenced by chlorine residual carryover from the pre-chlorination process, as presented in Section 6.2.1, on the anthracite filters in Train 1 (Filters 5 and 6). As a result, the ATP levels are low in the Train 1 anthracite filters from those sampling events.

For comparison, filter media from eight different facilities in North America with biofiltration (including anthracite or GAC media caps over a sand layer) ranged from 2,500 to 5.2 million pg ATP/g (Hooper et al. 2019). The filter media ATP levels in this pilot are on the lower side compared to the range of ATP media levels seen in these other full-scale biofiltration facilities, which is not surprising given the raw water low temperature and low organics levels. Also, those full-scale facilities have been operating biofiltration for several years. The observed levels in the pilot GAC filters would be comparable to ATP media levels observed at Halifax Water (~150,000 pg ATP/g dry media) (Hooper et al. 2019), which also has a cold, high quality source water.

Figure 7-13. Dry (adjusted) filter media ATP, December 2019–February 2020 prior to filter media change

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Overall, the ATP results were mostly influenced by the pretreatment mode, and to some extent by the media type. From December to January, the media ATP increased in Train 2 (Filters 1, 2, and 3), after longer operation with water exposed to ozone, while media ATP decreased in the Train 1 GAC filter (Filter 4) with pre-chlorine. The low ATP in Filters 5 and 6 was expected as a result of carryover of chlorine residual in the filter effluent for the anthracite filters. As of January 15, Train 2 had been ozonated for 58 days, while Train 1 had been pre-chlorinated for 49 days. While Train 1 transitioned to pre-ozone on January 21, there was not enough time before the February 3 sampling to see an impact of ozone on ATP in Train 1. Overall, ozone appears to increase media ATP compared to the GAC filter with pre-chlorination (Filter 4), consistent with other studies.

When the filters are compared within the individual train, it is evident that the GAC filters, Filter 2 (F2-GAC-60) and Filter 3 (F3-GAC-72), had higher ATP compared to the anthracite filter (F1-Anth-72). Pre-chlorination inhibited biological growth in Filters 4, 5, and 6 (Train 1). Therefore, all three filters had low ATP, making differences between the media less pronounced for the December and January sampling. The high ATP measured in the GAC filters compared to anthracite is consistent with other studies as well.

7.2.8.2 AOC Removal AOC is a measure of organic material available for microorganisms to metabolize and serves as an indicator to represent bacterial regrowth potential in distribution systems. By removing the AOC in the filtration process, there is less substrate for biological regrowth in the distribution system. Reduction of AOC is indicative of biomass acclimation. AOC is the fraction of DOC that can be easily assimilated by microorganisms and converted to cell biomass. Figure 7-14 shows the various forms of natural organic matter (NOM). Generally, for all NOM, roughly 50 percent is TOC, and DOC is roughly 80 to 90 percent of the TOC fraction (Crittenden et al. 2012).

Figure 7-14. Forms of natural organic matter (Adapted from Crittenden et al. 2012)

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AOC data observed for this pilot are presented below in Figure 7-15 for operations with pre- ozonation from August to October and in Figure 7-16, below, for operations with pre- chlorination and pre-ozonation until the media change out in early February. An overall statistical summary of the AOC data is presented below in Figure 7-17 for all samples collected from August 1, 2019, through January 29, 2020.

Hatched bars in both figures indicate samples that were pre-ozonated. Ozonation is expected to increase the amount of AOC in the treatment process as it breaks down the organic carbon into more readily biodegradable substrates, followed by removal through filtration. This process is generally observed in the filters between both time periods showing lower AOC in the filters with pre-ozonation. In addition, while treatment conditions were the same for Train 2 samples from September 11 and 25, there was considerable variability in the AOC results, indicating that AOC is inherently a variable parameter.

Figure 7-15. AOC concentration by sample location, August–October 2019 Hatched bars indicate pre-ozonation. No samples were collected at the ozone module outlet in either train for sampling events on August 1, 21, or September 11.

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Generally from August to October, the filters with pre-ozonation in Train 2 removed AOC from over 300 µg/L in the ozone effluent to below 50 µg/L in the filter effluent, with one exception for Filter 3 on September 25. The filters on Train 1, which operated without ozonation on September 11 and 25, showed a consistent decrease in the filtered effluent AOC from December 9 when ozonation was applied.

Figure 7-16. AOC concentration by sample location, November 2019-January 2020 Hatched bars indicate pre-ozonation

For the samples collected during the pre-chlorination testing, generally pre-chlorination inhibited biological activity compared to the pre-ozonated filters, indicated by higher AOC in the filter effluent from the pre-chlorinated filters. When comparing between just the anthracite filters, AOC was more comparable between pre-ozonated and pre-chlorinated trains than for the GAC filters. The use of pre-chlorine on December 2, 2019, and January 15, 2020, resulted in comparable results to using no oxidant on December 12 for Filters 5 (F5-Anth-60) and 6 (F6-Anth-72) in Train 1. This is expected given there was chlorine residual carryover from the pre-chlorination process onto the filters, inhibiting biological growth. Overall, AOC reduction from ozonation to filtered effluent increased the longer the filters were exposed to ozone treatment.

In addition to the trends observed for pre-ozonation, there appears to be slight differences in AOC reduction, and thus biological activity between the media types. Throughout the testing period, the GAC filters generally had lower AOC concentrations in the filtered effluent than their comparable anthracite filters. This trend is most evident when compared in the Train 2 filters between January 2 and January 15, 2020. For example, on January 2 the anthracite filter on Train 2 (F1-Anth-72) AOC was 56 µg/L compared to the GAC filters that were 24 µg/L and 35 µg/L for Filters 2 (F2-GAC-60) and 3 (F3-GAC-72), respectively. This same trend continued for

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the January 15 event, in which the anthracite filter was 150 µg/L compared to 50 µg/L and 120 µg/L in the GAC filters (Filters 2 and 3, respectively). GAC has a larger surface area, therefore the media can host a larger concentration of bacteria, and higher concentration of attached microbes, which contribute to more AOC reduction. These observations suggest the GAC filters have more biomass than on the anthracite filters.

When reviewing the 50th percentile of the AOC data (Figure 7-17), the filter effluent reduced the AOC concentration in the finished water from the raw water concentrations with both media types, with the exception of Filter 6 (F6-Anth-72). Train 2, which operated with more ozonation than Train 1, saw lower levels of AOC in the filtrate effluent, and appeared to generally reduce the AOC concentrations, which could indicate biomass acclimation. The differences between the media are not as distinct when evaluated from the full time period, compared to isolating the results to specific sample events, as presented in the figures above. For Train 1, the 50th percentile for the GAC 72-inch filter (F4-GAC-72) was 27 µg/L, which is slightly lower than the 50th percentiles for the anthracite filters (F5-Anth-60 and F6-Anth-72) on the same train of 35 and 64 µg/L, respectively. The 50th percentiles for the GAC filters on Train 2 are less distinct from the anthracite filter on the same train (F1-Anth-72), which were all low and about the same (5, 15, and 25 µg/L for Filters 1, 2, and 3, respectively). Additionally, in both trains, the 8 gpm/sf filter (60-inch) had lower AOC levels compared to the 12 gpm/sf filter with the same media. Impacts to AOC with changing filtration rate are discussed in more detail below in Section 7.3.10.1.

Figure 7-17. Statistical summary of AOC data, July 2019-January 2020

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7.2.8.3 Carboxylic Acids Removal One carboxylic acid sampling event occurred on January 15, 2020, prior to the media change out. Carboxylic acid data by location from January 15 are summarized in Figure 7-18 for Train 1 and Train 2, respectively, when the plant operated in a side-by-side comparison of pre- chlorination to pre-ozonation. Samples were analyzed with the RD 100 method measuring acetate (acetic acid), formate (formic acid), and oxalate (oxalic acid), each with an MRL of 10 µg/L. Results for both the pilot raw water and Filter 2 (F2-GAC-60) were below the MRL and depicted as half the MRL on the figures (5 µg/L).

Figure 7-18. Summary of carboxylic acid data collected on January 15, 2020

During this sampling time, Train 1 operated with pre-chlorine at a dose of 1.0 mg/L as Cl2, while Train 2 operated with pre-ozone at a dose of 1.0 mg/L as O3. Both trains were fed PACl (0.72 to 0.80 mg/L as Al3+) with nonionic filter aid (0.03 to 0.05 mg/L). In addition, anthracite filters (Filters 5 and 6) were influenced by chlorine residual carryover from the pre-chlorination process, as presented in Section 6.2.1. Train 2 had considerably higher carboxylic acids at the ozone outlet after ozonation, compared to pre-chlorination, indicating ozone is a stronger oxidant. Both trains showed a reduction in carboxylic acids through filtration, indicating that oxidation converts organic matter into more biodegradable substrate that is further removed as a result of biological activity in the filters. When comparing between filters not influenced by chlorine residual, Filter 1 (F1-Anth-72) had higher carboxylic acids than the GAC filter on Train 1, indicating the GAC filter resulted in further reduction in carboxylic acids than the anthracite filter for the January 15 sample. There were no consistent differences in the distribution of carboxylic acids between the media types. Oxalate was the most prominent carboxylic acid in Train 2, while formate and oxalate were both prominent in Train 1.

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7.2.8.4 EPS, Biofilm Morphology (SEM), and Enzyme Activity Assessment PWB contracted with the University of Texas-Austin (UT-Austin) to complete additional biological activity assessment between the GAC and anthracite filters. Samples were collected from Filter 1 (F1-Anth-72) with anthracite media (labeled as FM 104 in presented results) and Filter 3 (F3-GAC-72) with GAC media (labeled as FM 304 in presented results) on February 3, 2020. Results from the assessment are summarized in this section below from the assessment report provided by UT Austin (Kirisits 2020). Both filters were pre-ozonated for 68 days prior to sampling. Biological assessment included quantifying extracellular polymeric substances (EPS), evaluating biofilm morphology with a Scanning Electron Microscope (SEM), and measuring of enzyme activity. EPS were extracted from each homogenized sample using the method of Keithley and Kirisits 2018 (Keithley and Kirisits 2018). The filtrate containing EPS was analyzed for proteins and polysaccharides. The SEM Quanta 650 in the Texas Materials Institute at UT Austin was used in this assessment to visualize biofilm morphology. In addition, the activity of four extracellular enzymes (α-D-glucosidase, β-D-glucosidase, β-Nacetylglucosaminidase, and acid/alkaline phosphatase) was determined using an assay with fluorogenic substrates as outlined in Keithley and Kirisits 2019 (Keithley and Kirisits 2019).

EPS data are plotted in Figure 7-19 and tabulated in Table 7-8. The protein values are typical of what UT Austin has observed from other water treatment facility sampling, but the polysaccharides are on the higher side (but not out of ranges observed). Polysaccharides are correlated to EPS, which would contribute to head loss through the filter.

0.6

0.5

0.4

0.3

Proteins as mg BSA/g TS 0.2 Polysaccharides as mg Gluc/g TS or or TS Gluc/g as mg Polysaccharides 0.1

0 FM 104 FM 304 Polysaccharides as mg glucose/g TS Proteins as mg BSA/g TS Figure 7-19. EPS measured as polysaccharides and proteins in sample FM 104 (Filter 1, anthracite) compared to sample FM 304 (Filter 3, GAC) from February 3, 2020 Source: Kirisits 2020 FM 104 collected from Filter 1 (F1-Anth-72, 12 gpm/sf), FM 304 collected from Filter 3 (F3-GAC-72, 10 gpm/sf) Train 2 operation: Pre-ozone (1.0 mg/L O3) with PACl (1.3 mg/L), coagulant aid (0.5 mg/L), and nonionic filter aid (0.02 mg/L)

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Table 7-8. Tabulated EPS Proteins and Polysaccharides Proteins (mg BSA/g TS) Polysaccharides (mg glucose/g TS) Sample Filter Average Standard Deviation Average Standard Deviation FM104 Filter 1 (F1-Anth-72, 12 gpm/sf) 0.54 0.02 0.07 0.01 FM304 Filter 3 (F3-GAC-72, 10 gpm/sf) 0.46 0.00 0.25 0.00 Source: (Kirisits 2020)

SEM images from the filter samples are shown in Figure 7-20 for the anthracite filter and in Figure 7-21 for the GAC filter. Overall, the results indicate that the GAC filter (FM 304) has more biological activity compared to the anthracite filter (FM 104). Tendrils are observed in the SEM results (Figure 7-21) for Filter 3, which are likely EPS.

Figure 7-20. SEM images of samples taken from sample FM 104 (Filter 1, anthracite) Source: Kirisits 2020

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Figure 7-21. SEM images of samples taken from sample FM 304 (Filter 3, GAC) Source: Kirisits 2020

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Figure 7-22 shows the phosphatase to total glycosidase activity ratio (PHO:GLY ratio) in each filter. The PHO:GLY ratio is used to assess phosphorus limitations and potential EPS production. The PHO:GLY ratio for Filter 3 is near 40, which is higher than the UT Austin lab has observed for other full or pilot scale systems. The PHO:GLY ratios observed in the two samples indicate balanced growth, compared to water sources with higher PHO:GLY around 250, characterized by high EPS or filamentous biofilm morphology.

Figure 7-22. PHO: GLY ratio in each filter sample Source: Kirisits 2020

7.2.9 Chlorine Demand and Decay and Disinfection By-Products, and Flavor Profile Analysis

SDS testing was conducted to assess DBP formation and CDD in the treated water from each filter. Two rounds of SDS testing were conducted before the filter media were changed: one in late October, followed by another in mid-November.

CDD results are summarized from the two sampling periods by media types in Table 7-9. In October, for the free chlorine period, the CDD was greater in the anthracite filters. The CDD after the 14-day chloraminated incubation period, however, were all very similar between the filters, with no distinct differences. In November, within both trains, the CDD measured during the free chlorine contact period was slightly lower in samples from the GAC filters (Filters 3 and 4) than the anthracite filters (Filters 1 and 6). Within the filters with no pre-oxidant (Train 1), CDD calculated during both the free chlorine contact period and during the 14-day SDS period was lower in the GAC-filtered sample than the anthracite-filtered samples. GAC media appears to provide a small benefit in reducing chlorine demand.

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Table 7-9. Comparison by Media of CDD, October and November 2019 SDS Testing CDD (mg/L-Cl2) Train 1 Train 2

SDS Test Perioda Anthracite GAC Anthracite GAC (F6-72, 12 gpm/sf) (F4-72, 12 gpm/sf) (F1-72, 12 gpm/sf) (F3-72, 12 gpm/sf) Free Chlorine 14- Free Chlorine 14- Free Chlorine 14- Free Chlorine 14- Period day Period day Period day Period day Octoberb (Train 1 Pre-chlorination, 0.44 0.31 0.38 0.39 0.51 0.46 0.31 0.68 Train 2 Pre-ozonation) Novemberc (Train 1 No oxidant, 0.37 0.22 0.30 0.19 0.69 0.31 0.59 0.35 Train 2 Pre-ozonation) a. Samples were treated with disinfection (free chlorine contact and secondary disinfection with chloramines) and incubated for 14 days. b. For October sampling, Train 1 was pre-chlorinated with a dose of 0.3 mg/L as Cl2, and Train 2 was pre-ozonated with a dose of 1.0 mg/L as O3, both with 13 minutes of contact time. c. For November sampling, Train 1 was operated without a pre-oxidant, and Train 2 was pre-ozonated with a dose of 1.0 mg/L- O3 and 13 minutes of contact time prior to coagulant addition in the rapid mix tank.

The results shown in Table 7-10 represent the DBP formation observed following disinfection treatment and 14 days of incubation, comparing the results by media type. Although DBP values in SDS samples from the GAC columns were generally lower than those in the anthracite columns, DBP values in both were less than half of the water quality targets (40 µg/L TTHM, 30 µg/L HAA5), which, in turn, are set at half the MCLs for each constituent. DBP control in the filtered water produced by both media types is excellent. For further details on SDS testing, please refer to Appendix B.

Table 7-10. Comparison by Media of 14-day DBP Formation, October and November 2019 SDS Testing Train 1 Train 2b Anthracite GAC Anthracite GAC SDS Test Perioda (F6-72, 12 gpm/sf) (F4-72, 12 gpm/sf) (F1-72, 12 gpm/sf) (F3-72, 12 gpm/sf) TTHM HAA5 TTHM HAA5 TTHM HAA5 TTHM HAA5 Octoberc (Train 1 Pre-chlorination, 14.1 10.8 9.7 7.4 8.5 5.0 10.4 5.8 Train 2 Pre-ozonation) Novemberd (Train 1 No oxidant, 8.4 6.4 7.9 5.2 6.7 5.5 4.9 4.4 Train 2 Pre-ozonation) a. Samples were treated with disinfection (free chlorine contact and secondary disinfection with chloramines) and incubated for 14 days prior to analysis. b. During the SDS testing, calcium thiosulfate was dosed at 0.25 mg/L to quench the ozone residual. Calcium thiosulfate can exert a demand on chlorine, therefore the results for the CDD in Train 2 with pre-ozonation are conservative and reflect additional demand of up to 0.25 mg/L from calcium thiosulfate. c. For October sampling, Train 1 was pre-chlorinated with a dose of 0.3 mg/L as Cl2, and Train 2 was pre-ozonated with a dose of 1.0 mg/L as O3, both with 13 minutes of contact time. d. For November sampling, Train 1 was operated without a pre-oxidant, and Train 2 was pre-ozonated with a dose of 1.0 mg/L- O3 and 13 minutes of contact time prior to coagulant addition in the rapid mix tank.

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The November 2019 test included a taste and odor evaluation in addition to sampling for disinfectant residual and DBP concentrations. The taste and odor of pilot plant-treated water was assessed through FRA (Standard Method 2160) and FPA (Standard Method 2170), by the Seattle Public Utilities (SPU) Flavor Profile Panel. Members of the panel tasted each sample and assigned an FRA rating between 1 and 9, which is a measure of the acceptability or offensiveness of the water, with 1 being “very happy to accept as their everyday drinking water.” The panel members generally found the filtered water samples to be highly acceptable as their everyday drinking water and assigned the highest FRA score of 1.0 to all filtered samples with the exception of Filter 5, which scored slightly higher at 1.75. The evaluation did not show any distinct differences between filtered samples treated with ozone and/or GAC. For further details on the testing, please refer to Appendix C, November SDS Testing Report.

7.2.10 Summary

Between June 2019 and February 2020, the performance of the anthracite and GAC filter medias were compared; a summary of results are shown in Table 7-11. The GAC media filter effluent had lower levels for organic constituents and DBPs compared to the anthracite media filters. However, the anthracite filters had good organics removal as well and experienced higher UFRVs, and thus improved filter productivity. The deeper bed GAC filters, operated at 12 gpm/sf, were hindered by their CBHL. It is not completely certain the causation for the increased CBHL. The GAC filters had silica sand with a smaller effective size, but the CBHL increased in the GAC filters over time and above would be expected given the seasonally declining water temperatures. Biological monitoring indicated the GAC media filters produced more biologically stable water compared to anthracite filters. Given the fact that filtration performance was better in the anthracite filters, the anthracite filters had good organics removal, and anthracite media is less expensive, it was recommended that the GAC media be swapped with additional anthracite media to allow for more scrutiny of the effective size, media depth, and filtration rates.

Table 7-11. Filter Media Comparison Summary Filter Factor Units Anthracite GACa Unit Filter Run Volume (UFRV)b gal/sf 7,500–11,500 6,500–10,000 TOC Removalc % 45–52 60–62 DBPs: TTHMsd µg/L 6.7–14.1 4.9– 10.4 DBPs: HAA5sd µg/L 5.0–10.8 4.4–7.4 a. GAC filter media life was less than 8 months old. b. Range of median (50th percentile) UFRVs from the 12 gpm/sf anthracite or GAC filters from August 20 to December 17, 2019. c. Minimum and maximum TOC removal from the 12 gpm/sf anthracite or GAC filters from August 20 to December 17, 2019. TOC removal based on a comparison of raw water and filtered water. d. Minimum and maximum DBP formation from October and November SDS testing. The DBP information presented is based on a 14-day water age from SDS testing.

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7.3 Filtration Rate Comparison

After the original filter media were removed in February 2020, the filters were rebuilt with three anthracite media profiles, mirrored on both trains, each of which was designed for a different filtration rate: 8, 10, or 12 gpm/sf. This section compares filter performance of each filter design, through operations from February 24–May 24, 2020. The testing period includes the period from February 24 to March 10, when both trains were operated with pre-ozonation right after the media change, followed by the side-by-side comparison of intermediate ozonation (Train 1) and pre-ozonation (Train 2). Data in Appendix F evaluates the impact of filtration rate on both GAC and anthracite media during the first 7 months of the study.

CBHL will be presented along with filter performance evaluated with filter effluent turbidity, run time, UFRV, and organics removal, with the goal to compare the filter designs and filtration rates tested.

7.3.1 Clean Bed Head Loss

Figure 7-23 presents the observed CBHL in each column from February 24 through May 12, 2020, during which each filter media profile was operated at its design filtration rate. There are three distinct groupings of CBHL data, each corresponding to the three filtration rates tested.

Figure 7-23. Clean bed head loss over time for all filters, February 24-May 12, 2020

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From February 24 to March 28, the CBHL increased gradually in all filters, corresponding to the start-up and acclimation period after the media rebuild. During that period, the filters operated with pre-ozonation until March 10 when Train 1 filters switched to intermediate ozonation. The amount of head loss buildup during that first period increased with filtration rate consistently in both trains. Head loss in the 12 gpm/sf filters (Filters 3,4) increased by about 1.0 foot for both filters, while the 8 gpm/sf filters increased by about 0.75 feet and the 6 gpm/sf filters increased by about 0.5 feet. The CBHL leveled off for most of the filters with fluctuations of about 1 foot, until around April 20, when Filter 2 started to accumulate more head loss, while Filter 5 head loss gradually decreased, both by about 0.25 feet. Generally, the CBHLs from the Train 1 filters (Filters 4, 5, and 6) tended to be slightly lower than the CBHLs from the corresponding Train 2 filters (Filters 1, 2, and 3) up to about 0.25 feet. Nonetheless, the difference between the two trains was relatively minor compared to the differences previously observed between the GAC and anthracite media.

7.3.2 Turbidity

Figure 7-24 shows the filter effluent turbidities recorded during accepted filter runs throughout the period of filtration rate testing when each filter media profile was operated at its design filtration rate. Analysis includes the entire period, with no differentiation based on pretreatment.

Figure 7-24. Filter effluent turbidities recorded, February 24-May 12, 2020

Overall, filter effluent turbidities were well-controlled on all six filters at all filtration rate configurations, each of which had 75th percentiles under 0.05 NTU. The 95th percentiles were higher, but still under 0.1 NTU, because those data points were representative of the period immediately after a FTW period or the period at the end of a filter run, prior to backwashing. Filters 5 and 6 were exceptionally consistent, although all filters had relatively narrow bands of filter effluent turbidities.

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These data show that filtration rate did not appear to significantly impact the filter effluent turbidity during this trial period, and that all filters can meet the regulatory requirements for turbidity for all filtration rates tested during this period (8, 10, and 12 gpm/sf).

Figure 7-25 presents two example filter runs from this testing period, comparing performance between the higher and lower filtration rates. Both Filter 4 (F4-Anth-72, 12 gpm/sf) and Filter 6 (F6-Anth-60, 8 gpm/sf) terminated their filter runs due to head loss. These filter runs are examples of typical runs during the time period where both turbidity and particle counts were very low.

Figure 7-25. Filter run examples for loading rate testing

7.3.3 Particle Counts

Total particle counts are summarized in Figure 7-26 from February 24 to May 12 for all accepted filter runs. This testing duration includes the period from February 24 to March 10 when both trains were operated with pre-ozonation right after the media change, followed by the first month of the side-by-side comparison of intermediate ozonation (Train 1) and pre- ozonation (Train 2) when filter aid dosing was refined, and the last month from April 3 to May 12 once operations stabilized.

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It is clear from Figure 7-26 that, while the variability in the particle counts appears to increase with filtration rate, the median particle counts are similar between the filters, all well below 25 counts/mL. Operations from March 10 to March 28 involved frequent changes to chemical dosing to improve filter productivity. Through this period, the chemical dosing strategy was improved by raising the coagulant dose and changing the filter aid dose location from the combined filter skid inlets to the individual filter inlets. During this time, the 12 gpm/sf filters were noted to have insufficient backwashing for some runs, and therefore higher filter effluent particle counts.

Figure 7-26. Total particle counts from all filters, February 24-May 12, 2020 Given the start-up conditions following filter media changeout, Table 7-12 presents a subset of the operational period from April 3 to May 12. During this period, the pilot operated with intermediate (Train 1) and pre-ozonation (Train 2). The performance was excellent for all filters at each filtration rate, with all filters meeting the goal of having less than 50 particles/mL in the 5 to 15 µm range. All filters had greater than 2.0-log removal for 3 to 5 µm range and 2.5-log for 5 to 15 µm range. The 95th percentiles of the particle counts in the 3 to 5 µm and 5 to 15 µm size ranges were all low and similar between filters. In the intermediate train, there were slightly higher particle counts in the higher filtration rate filters (12 gpm/sf) compared to the 8 gpm/sf filters; however, the differences were minor. These data demonstrate that particles are sufficiently removed for each of the three filter media designs tested with filtration rates from 8 to 12 gpm/sf. Additionally, as demonstrated above in Figure 7-25 for two individual filter runs, the performance for Filters 4 and 6 (8 gpm/sf and 12 gpm/sf, respectively) was excellent, with low effluent particle counts in both.

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Table 7-12. Raw Water and Filter Effluent Particle Counts Summary, April 3–May 12, 2020 Sampling Location Raw Water Parameter 50th Percentile 95th Percentile Turbidity (NTU) 0.32 0.61 Particles 3 to 5 µm 1,172 1,622 (particles/mL) 5 to 15 µm 953 1,148 Testing Condition Train 2: Pre-Ozone Train 1: Intermediate Ozone 50th 95th Average Log 50th 95th Average Log Parameter Percentile Percentile Removala Percentile Percentile Removala Filter Configuration F1–Anth–60, 8 gpm/sf F6–Anth–60, 8 gpm/sf Turbidity (NTU) 0.01 0.06 0.01 0.01 Particles 3 to 5 µm 2 8 2.7 1 2 3.0 (particles/mL) 5 to 15 µm 2 6 2.7 1 4 2.8 Filter Configuration F2–Anth–66, 10 gpm/sf F5–Anth–66, 10 gpm/sf Turbidity (NTU) 0.01 0.03 0.01 0.01 d Particles 3 to 5 µm 2 22 2.6 1 4 2.9 (particles/mL) 5 to 15 µm 2 17d 2.5 1 5 2.8 Filter Configuration F3–Anth–72, 12 gpm/sf F4–Anth–72, 12 gpm/sf Turbidity (NTU) 0.01 0.02 0.01 0.02 Particles 3 to 5 µm 2 10 2.7 2 7 2.8 (particles/mL) 5 to 15 µm 2 6 2.7 2 7 2.7 a. Average log removals are calculated based on averaging log removals from paired data (raw water and filter effluent for the same aliquot of water based on the HRT) when raw water particles in the indicated size range exceeded 500 particles/mL

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7.3.4 Filter Run Times and UFRVs

Figures 7-27 and 7-28 present the observed run times and UFRVs, respectively, for the period during which the filter media profiles were operated at their design filtration rates from February 24 to May 12. The testing period includes the period from February 24 to March 10, when both trains were operated with pre-ozonation right after the media change, followed by the side-by-side comparison of intermediate ozonation (Train 1) and pre-ozonation (Train 2).

Figure 7-27. Filter run hours for accepted filter runs, February 24-May 12, 2020

Figure 7-28. Filter UFRVs for accepted filter runs, February 24-May 12, 2020

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For all filtration rates, median UFRVs were above the desired UFRV goal of 10,000 gal/sf. The minimum UFRV goal of 6,500 gal/sf for 95 percent of the time was achieved, with the exception of Filter 5, which was slightly under the 6,500 gal/sf goal. For Train 1 filters, median productivity varied proportionally with filtration rate. On Train 2 filters, median UFRVs at 8 and 10 gpm/sf were similar, and both more productive than the 12 gpm/sf filter. For both trains, run times for the 12 gpm/sf filters also tended to fall below 24 hours, suggesting that filters would need to be backwashed more than once per day if the full-scale facility were operated under similar conditions.

7.3.5 Head Loss Threshold Comparison

The full-scale design may be limited to a 10-foot head loss threshold due to hydraulic constraints. Therefore, the data used to determine the UFRVs presented above in Figure 7-28 were revaluated against the lower 10-foot threshold to determine how filter productivity may be impacted.

The results of this analysis are presented side-by-side with the filter run time and corresponding UFRV data to illustrate the impact that reducing the terminal head loss threshold would have on filter productivity (Figure 7-29 and Figure 7-30, respectively).

Figure 7-29. Filter run time when terminated on 10 ft of head loss compared to 12 ft of head loss for accepted filter runs, February 24-May 12, 2020

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Figure 7-30. Filter UFRVs when terminated on 10 ft of head loss compared to 12 ft of head loss for accepted filter runs, February 24–May 12, 2020

In addition, Table 7-13 compares the average UFRVs for each filter from this period, as calculated with both the 12-foot and 10-foot terminal head loss thresholds. Overall, the lower terminal head loss threshold reduced filter productivity by 15 to 25 percent, depending on the filter. At both head loss thresholds, all filters had median and average UFRVs above the goal of 10,000 gal/sf (Figure 7-30, Table 7-13); however, only the filters operated at 8 gpm/sf were able to consistently meet this goal throughout the operational period.

Table 7-13. UFRV Averages for 10- and 12-ft Head Loss Threshold Filter F1-Anth-60, F2-Anth-66, F3-Anth-72, F4-Anth-72, F5-Anth-66, F6-Anth-60, Filtration rate, gpm/sf 8 gpm/sf 10 gpm/sf 12 gpm/sf 12 gpm/sf 10 gpm/sf 8 gpm/sf 10 ft Head loss 15,817 16,533 12,586 12,071 15,363 16,659 12 ft Head loss 18,434 20,243 15,726 14,650 18,380 19,168 % Difference between 12 ft and 10 ft 17% 22% 25% 21% 20% 15%

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7.3.6 Filter Efficiency

Figure 7-31 presents a summary of the FTW as a portion of the overall filter production. The pilot study had set a goal that the FTW would be less than 5 percent of the filter production or the filters would have a 95 percent efficiency for 95 percent of the operational time. The triangle on the box-whisker plot represents the 95th percentiles. If the FTW was recorded as zero minutes in the HMI because the FTW time was less than 5 minutes, 5 minutes was used for this assessment to be conservative.

All of the filters had 5th percentile efficiencies greater than 97 percent and surpassed the water production goal defined in Table 1-1. The FTW cycle represented less than 3 percent of production and the goal was to be less than 5 percent. This corresponds to a 95th percentile FTW length ranging from 10 to 30 minutes. The filter loading rate did not negatively impact filter efficiency. The highest loading rate filters (Filters 3 and 4) had the highest efficiencies.

Figure 7-31. Comparison of filter efficiency by filtration rate

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7.3.7 Organics Removal

Average removals for TOC and UV254 from the raw water to filtered effluent are presented below in Tables 7-14 and 7-15. Removal for all organics was fairly consistent across the filtration rates, with improved TOC removal in the pre-ozonated train. TOC removals ranged from 32 to 37 percent, with the higher average removals seen in Filters 2 and 3. UV254 and color removals were similar across all filters. UV254 reduction ranged from 77 to 81 percent, while color was reduced from an average of 5.0 Pt-Co to below the MRL for all samples (3 Pt-Co), with no noticeable trend based on filter or filtration rate.

Table 7-14. Average TOC Removal by Filter, February 24-May 12, 2020 TOC Average Removal Sample Location Average TOC (mg/L) Average Percent Removala No. of Samples Std Dev Raw Water 0.82 -- 20 0.07 F1-Anth-60, 8 gpm/sf 0.53 35% 20 0.13 F2-Anth-66, 10 gpm/sf 0.52 37% 20 0.10 F3-Anth-72, 12 gpm/sf 0.52 37% 20 0.08 F4-Anth-72, 12gpm/sf 0.55 33% 19 0.07 F5-Anth-66, 10 gpm/sf 0.56 32% 19 0.09 F6-Anth-60, 8 gpm/sf 0.53 35% 19 0.07 a. Average TOC removals were determined by averaging the computed daily removal of TOC between raw and individual filter effluent.

Table 7-15. Average UV254 Reduction by Filter, February 24-May 12, 2020

UV254 Average Reduction

Sample Location Average UV254 Average Percent No. of Samples Std Dev (cm-1) Reductiona Raw Water 0.034 -- 26 0.007 F1-Anth-60, 8 gpm/sf 0.005 80% 26 0.002 F2-Anth-66, 10 gpm/sf 0.005 77% 26 0.002 F3-Anth-72, 12 gpm/sf 0.004 81% 26 0.003 F4-Anth-72, 12 gpm/sf 0.005 79% 26 0.002 F5-Anth-66, 10 gpm/sf 0.005 78% 26 0.002 F6-Anth-60, 8 gpm/sf 0.005 80% 26 0.002 a. Average reduction of UV254 were determined by averaging the computed daily reduction of UV254 between raw and individual filter effluent.

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7.3.8 Metals and Inorganics

Total aluminum, iron, and manganese concentrations that were measured in the filter effluent through the filtration rate comparison period, February 24–May 12, 2020, are presented in this section. Figure 7-32 and Figure 7-33 present the total aluminum concentrations measured in the effluent of the Trains 1 and 2, respectively. Throughout this period, effluent total aluminum concentrations in all media types were below 50 µg/L, with a median concentration of 16.7 µg/L in Train 1 and a median concentration of 17 µg/L in Train 2. Raw water aluminum concentrations during this time ranged from 21 µg/L and 44 µg/L. This suggest that, for the operating conditions evaluated during this period, the pilot treatment process effectively removed total aluminum. Compared to the 2019 observations presented in Section 7.2.7, there was no apparent breakthrough of particulate aluminum hydroxide floc during this period.

Figure 7-32. Total aluminum in Train 1 filter effluent, February 24–May 12, 2020

Figure 7-33. Total aluminum in Train 2 filter effluent, February 24–May 12, 2020

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Total iron concentrations in both the raw water and the filter effluent were all below detection limit (presented as half the MRL) throughout this testing period, as shown in Figure 7-34 and Figure 7-35.

Figure 7-34. Total iron in Train 1 filter effluent, February 24–May 12, 2020

Figure 7-35. Total iron in Train 2 filter effluent, February 24–May 12, 2020

Throughout the filtration rate comparison trial, filter effluent total manganese concentrations were less than 1.1 µg/L, as shown in Figure 7-36 and Figure 7-37. During this period, raw water manganese concentrations ranged from 1.3 µg/L and 1.7 µg/L.

Figure 7-36. Total manganese in Train 1 filter effluent, February 24-May 12, 2020

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Figure 7-37. Total manganese in Train 2 filter effluent, February 24-May 12, 2020 For all inorganic constituents evaluated, there was no apparent difference in removal based on filtration rate or filter configuration.

7.3.9 Filtration Rate Comparison Trial

This section focuses on filter performance of each filter design during a 2-week period in May 2020 during which each filter media profile was operated over a range of four filtration rates: 6, 8, 10, and 12 gpm/sf. Specifically, this trial was designed to investigate filter performance at filtration rates that were above and below the designated design filtration rates. For example, Filters 1 and 6, with a 60-inch media depth, were designed to operate at 8 gpm/sf and were tested up to 12 gpm/sf. This test was important to understand because the filtration facility will normally operate at some lower production level than the design capacity, and because it is desired to choose a robust design that has some flexibility to turn up the production level in an emergency (within regulatory approved rates) without compromising filtered water quality and productivity goals.

Initially, filter effluent turbidity and particle counts are presented showing there is minimal direct impact on those parameters with changing filtration rate. Next, UFRVs, filter run time, and head loss accumulation are presented, demonstrating distinct differences in UFRVs by filtration rate (and the corresponding filter run times), which are directly related to changes in head loss accumulation. Additionally, filter productivity is compared between a head loss threshold of 10 feet compared to 12 feet to see if the performance goals are met at a lower head loss threshold.

7.3.9.1 Filter Effluent Turbidity Filter effluent turbidity over the study period is shown below in Table 7-16, along with the turbidity threshold of 0.1 NTU. Overall, effluent turbidity was generally well below the 0.1 NTU goal for all filters. In addition, filter effluent turbidity did not vary with changes in the filtration rate from 6 gpm/sf to 12 gpm/sf across all filters and trains. This demonstrates that even the coarse media designs at low filtration rates can meet water quality goals. This was achieved with control of pretreatment processes and because filter aid dosing was adjusted to target similar filter effluent quality.

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Table 7-16. Turbidity for each Filter Design with Pre-Ozonation, over all Filtration Rates Tested, May 12-May 26, 2020 60-inch Media, gpm/sf 66-inch Media, gpm/sf 72-inch Media, gpm/sf

6 8 10 12 6 8 10 12 6 8 10 12 No. of Samples 2,144 2,105 1,416 1,472 1,627 2,136 869 1,232 1,673 1,366 1,361 1,396 95th Percentile 0.07 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.02 0.06 0.04 0.01 50th Percentile 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01

7.3.9.2 Particle Counts Tables 7-17 and 7-18 show the particle counts recorded during the test period. Consistent with other filter performance metrics during this period, the particle counts were consistently below the goal of less than 50 particles/mL for all filtration rates. These data again demonstrate that all filter designs tested were able to meet water quality goals at each of the tested filtration rates.

Table 7-17. Ozonated Water and Filter Effluent Particle Counts Summary, May 12-May 18, 2020 Sampling Location Ozonated Watera Parameter 50th Percentile 95th Percentile Turbidity (NTU) 0.27 0.32

Particles 3 to 5 µm 450 825 (particles/mL) 5 to 15 µm 220 719 Testing Condition Train 2, pre-ozonation: 12 gpm/sfb Train 1, pre-ozonation: 10 gpm/sfb Parameter 50th Percentile 95th Percentile 50th Percentile 95th Percentile Filter Configuration F1–Anth–60, 12 gpm/sf F6–Anth–60, 10 gpm/sf Turbidity (NTU) 0.01 0.01 0.01 0.01

Particles 3 to 5 µm 2 9 2 5 (particles/mL) 5 to 15 µm 5 11 4 9 Filter Configuration F2–Anth–66, 12 gpm/sf F5–Anth–66, 10 gpm/sf Turbidity (NTU) 0.01 0.01 0.01 0.01

Particles 3 to 5 µm 3 6 2 5 (particles/mL) 5 to 15 µm 6 10 4 7 Filter Configuration F3–Anth–72, 12 gpm/sf F4–Anth–72, 10 gpm/sf Turbidity (NTU) 0.01 0.04 0.01 0.01

Particles 3 to 5 µm 3 11 2 4 (particles/mL) 5 to 15 µm 6 14 4 7 a. Train 1 was ozonated during this period, therefore particle counts are post-ozonation. Particle counts may be lower than would be expected in untreated raw water. Ozonated water data are based on 1,646 to 1,706 number of samples. b. Filtrate data in Trains 1 and 2 are based on 509 to 1,472 number of samples.

Particle count log removals are not presented during the filtration rate period from May 12– May 27, 2020 because the influent counts were conservatively lower (< 500 particles/mL) than would have been in true raw water as a result of the influence from ozonation. Because of an

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operational limitation of the pilot system, the particle counter at the Floc/Sed 1000 train inlet sampled ozonated water during pre-ozone testing instead of raw water. Ozone lowered the particle counts likely due to breaking particles apart into sizes smaller than the < 2 µm threshold of the counter, and therefore less of the original raw water particles were counted. As a result, the log removals are not presented.

Table 7-18. Ozonated Water and Filter Effluent Particle Counts Summary, May 18-May 27, 2020 Sampling Location Ozonated Watera Parameter 50th Percentile 95th Percentile Turbidity (NTU) 0.22 0.29

Particles 3 to 5 µm 394 504 (particles/mL) 5 to 15 µm 220 336 Testing Condition Train 2, pre-ozonation: 6 gpm/sfb Train 1, pre-ozonation: 8 gpm/sfb Parameter 50th Percentile 95th Percentile 50th Percentile 95th Percentile Filter Configuration F1–Anth–60, 6 gpm/sf F6–Anth–60, 8 gpm/sf Turbidity (NTU) 0.01 0.01 0.01 0.07

Particles 3 to 5 µm 2 9 2 43 (particles/mL) 5 to 15 µm 5 10 3 58 Filter Configuration F2–Anth–66, 6 gpm/sf F5–Anth–66, 8 gpm/sf Turbidity (NTU) 0.01 0.01 0.01 0.01

Particles 3 to 5 µm 2 7 2 8 (particles/mL) 5 to 15 µm 4 9 3 11 Filter Configuration F3–Anth–72, 6 gpm/sf F4–Anth–72, 8 gpm/sf Turbidity (NTU) 0.01 0.06 0.01 0.02

Particles 3 to 5 µm 2 33 2 10 (particles/mL) 5 to 15 µm 4 41 4 14 a. Train 1 was ozonated during this period, therefore particle counts are post-ozonation. Particle counts may be lower than would be expected in untreated raw water. Ozonated water data are based on 2,272 to 2,395 number of samples. b. Filtrate data in Trains 1 and 2 are based on 925 to 2,144 number of samples.

7.3.9.3 Filter Run Time and UFRVs Figure 7-38 presents the run times for each filter over the filtration rate comparison trial period. As expected, run times decrease as filtration rate increases, and for a given filtration rate, run time increases as filter media depth and media effective size increases (allowing for more space to retain filtered materials). UFRV data from Trains 1 and 2 are presented in Figure 7-39, comparing operation with filtration rates ranging from 6 to 12 gpm/sf. During this period, all representative runs were terminated due to exceeding 12 feet of head loss. Additionally, there were some filter runs that were manually backwashed when switching treatment conditions—because these runs were artificially shortened when switching treatment, they have been excluded from the data set as non-representative data.

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Figure 7-38. Average run time with pre-ozonation, over all filtration rates testing, May 12-May 26, 2020 Bar plots represent average value with the minimum and maximum shown with brackets. Filter configurations at the design configuration were 60-inch at 8 gpm/sf, 66-inch at 10 gpm/sf, and 72-inch at 12 gpm/sf.

Figure 7-39. Average UFRVs with pre-ozonation, over all filtration rates testing, May 12-May 26, 2020 Bar plots represent average value with the minimum and maximum shown with brackets. Filter configurations at the design configuration were 60-inch at 8 gpm/sf, 66-inch at 10 gpm/sf, and 72-inch at 12 gpm/sf

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As per the experimental plan, the number of filter runs collected during the low-filtration rate testing was limited because of the very long (>60 hour) run times. Filters 3, 4, and 5 each had a filter run that surpassed the UFRV goal of 10,000 gal/sf-run, but their filter runs were terminated early through initiation of a manual backwash in order to switch to the next operational scheme. These filter runs were not included in the UFRV summaries shown in Figure 7-39. They are summarized in Table 7-19 because they represent a value that the UFRV would have reached if it had been allowed to continue operation. For example, when the filter run for Filter 3 was terminated, the head loss was at 6.8 ft. If a linear head loss accumulation is assumed and the Filter 3 operation was allowed to continue, the resultant UFRV from that run is estimated to be greater than 18,000 gal/sf-run.

Table 7-19. Filter Runs Removed from Analysis Due to Early Manual Termination F3-Anth-72 F4-Anth-72 F5-Anth-66 Filter Run UFRV, gal/sf-run 10,672 14,344 15,699 Terminal Head Loss, ft 6.80 6.57 7.47 Terminal Turbidity, NTU 0.01 0.01 0.01 Head loss Accumulation Rate 0.16 0.11 0.12 Estimated UFRVa, gal/sf-run >18,000 >26,000 >25,000 a. Estimated UFRV if filter run had been allowed to continue to terminal head loss and filter run was not terminated via a manual backwash for operational change.

All filters generally maintained excellent filter effluent quality throughout their runs, until the developed head loss triggered a filter backwash. This consistent filtration performance was due to excellent pre-oxidation, filter aid dosing, and coagulation conditions resulting in easily filterable floc, speaking to the experience gained by the operations team in learning to operate the pilot treatment facility over the course of the year-long testing.

For the higher filtration rate period, the UFRVs started out below the 10,000 gal/sf goal for four of six filters and increased over time in all filters. The ozone system had issues with feeding the target dose between May 12–14, resulting in an ozone dose of only 0.4 mg/L as O3 for Train 1, and 0.1 mg/L as O3 for Train 2, which could explain the shorter filter runs and lower UFRVs toward the start of the period. Filter aid was also decreased at the start of the trial to improve performance from about 0.025 mg/L to 0.018 mg/L for Train 1 filters, and from 0.02 mg/L to 0.013 mg/L for Filter 1 and Filter 2, and 0.014 mg/L for Filter 3.

For Filters 4, 5, and 6, lowering the filtration rate from 12 gpm/sf to 6 gpm/sf increased the observed average UFRVs by 111–133 percent, while lowering the filtration rate from 10 gpm/sf to 8 gpm/sf for Filters 1, 2, and 3 increased the observed average UFRVs by 31–48 percent (Figure 7-39). The coarser and deeper filter profile (Filters 3 and 4) did best at both the high filtration rates (12 gpm/sf for Filter 4 and 10 gpm/sf for Filter 3) and the lower filtration rates when the head loss was allowed to accumulate up to 12 feet. Increasing the bed depth from 60 inches to 66 inches increased the UFRV on average by 8–27 percent, and increasing the bed depth from 66 inches to 72 inches increased the UFRV on average by 3–18 percent (Figure 7-39).

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For all filters, the changes in UFRVs with filtration rate indicate that, for these test conditions, operating the filters at higher filtration rates reduces overall productivity. The average UFRVs for filtration rates of 6 and 8 gpm/sf can be considered excellent for all conditions as the average value for each filter is well above the goal of 10,000 gal/sf, as seen in Figure 7-39 above. UFRVs were still acceptable at 10 gpm/sf with all of the average UFRVs in excess of the 10,000 gal/sf goal, but the 60-inch column (Filter 1) had filter runs with UFRVs below the 10,000 gal/sf goal. At the highest filtration rate tested, 12 gpm/sf, the average UFRV was above the 10,000 gal/sf goal for the 72-inch and 66-inch media configurations (Filters 4 and 5). The 60-inch column (Filter 6) average UFRV was slightly below the 10,000 gal/sf goal, but still above the performance goal of 6,500 gal/sf for 95 percent of the operational time.

7.3.9.4 Head Loss Accumulation Rate During this testing period, the filters all effectively removed turbidity to below 0.1 NTU (Section 7.3.9.1); thus, the only parameter controlling the length of the filter runs during this period was the rate at which head loss accumulated in the filters. The head loss in the filters is directly related to the velocity of the flow through the media void spaces (space between filter media particles), which, in turn, is directly related to the filtration rate. Therefore, filtration rate impacts both the CBHL and head loss accumulation. Outside of filtration rate, the rate at which head loss accumulates in the filters is impacted by the extent to which the filter’s void spaces become filled with particles and/or other material filtered from the filter influent, which is associated with the media effective size and the depth of the total column and each individual layer. Figure 7-40 presents the filter head loss accumulation over the course of the filter run for each filter, at the four filtration rates. Each individual curve represents an acceptable filter run. The differences in the number of filter runs was a result of shorter (and therefore more) filter runs at the higher filtration rates. As expected, the slopes of the head loss curves (representing the head loss accumulation rate for each filter run) are directly related to the difference in filtration rate—as the filtration rate increases, the head loss curve becomes steeper. As expected, the head loss accumulation rate was highest for the filter with the 60-inch media depth, which has smaller media and a “tighter” filter composition. Interestingly, the head loss accumulation in the 66-inch and 72-inch depth filters was similar for several runs when compared against the range of observed data (i.e., head loss curves were similar when looking at the overall range of observations, even if they may have differed when comparing runs conducted side-by-side during the period). The similarity can be attributed to ineffective backwashing on the 72-inch filters, resulting in more retained solids than expected. This could have made the head loss characteristics appear to be similar to the tighter filter that would have had somewhat higher CBHL at the same flowrate, despite being a shorter column. The wide range of head loss accumulation rates during this period, particularly for the tests at 10 and 12 gpm/sf, was surprising. The variability was likely because of operational modifications made during the test period to increase the length of the filter runs and to lower the head loss accumulation rate by lowering the filter aid dose. These data suggest that the filters are very responsive to filter aid. It appears that relatively small dose changes can have a significant impact on head loss accumulation rate and, thus, on filter productivity in terms of run time and UFRV. These pilot results suggest that the filter aid feed system in the full-scale

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treatment facility may need a high level of granularity in chemical dosing to allow for fine-tuned adjustments to the filter aid feed. Figure 7-41 through Figure 7-43 present the filter runs separated by each filter bed depth (60 inches, 66 inches, and 72 inches, respectively) to more directly see the impact filter bed depth and media effective size has on head loss accumulation. These results show a clear difference between the 60-inch filters and the 66- and 72-inch filters. At all flow rates, the 60-inch filters accumulated head loss more rapidly than the 66- and 72-inch filters. The accumulated head loss impacted the filter productivity (i.e., UFRVs) as discussed in the subsequent section. There was less overall difference in head loss accumulation rate between the 66-inch and 72-inch filters as each of these filters had head loss accumulation rates that fell within similar ranges. However, comparing observed filter UFRVs, shown in Figure 7-40, suggests that on a side-by-side basis, the 72-inch filters were slightly more productive than the 66-inch filters. Again, as mentioned above, the difference between the 72-inch and 66-inch filters would have likely been greater if the 72-inch filters were effectively backwashed.

Figure 7-40. Head loss accumulation by filtration rate (6, 8, 10, and 12 gpm/sf) for each acceptable filter run, May 12-May 26, 2020

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Figure 7-41. Head loss accumulation for the 60-inch media filters at all filtration rates (6, 8, 10, and 12 gpm/sf) for each acceptable filter run, May 12-May 26, 2020

Figure 7-42. Head loss accumulation for the 66-inch media filters at all filtration rates (6, 8, 10, and 12 gpm/sf) for each acceptable filter run, May 12-May 26, 2020

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Figure 7-43. Head loss accumulation curves for the 72-inch media filters at all filtration rates (6, 8, 10, and 12 gpm/sf) for each acceptable filter run, May 12-May 26, 2020 Based on the data presented above, the 60-inch filters were less productive than the other filter media profiles. Performance between the 66- and 72-inch filters was comparable; however, there would be a tradeoff between the slightly higher productivity in the 72-inch filters and the increased cost of media and the hydraulic impact of having an extra 6 inches of filter media).

7.3.9.5 Head Loss Threshold Comparison As discussed in Section 7.3.4, the full-scale design may be limited to a 10-foot head loss threshold used to establish the end of the run when evaluating filter run times and the associated UFRVs. Figure 7-44 and Figure 7-45 present the average UFRVs for all filters with the 10 foot threshold compared to the 12-foot threshold, as discussed in the above section.

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Figure 7-44. Average UFRV for Train 1 (12 gpm/sf) and Train 2 (10 gpm/sf) both with pre-ozonation evaluated with the 10-ft head loss threshold compared to 12-ft threshold, May 12–May 18, 2020 Bar plots represent average value with the minimum and maximum shown with brackets. Filter 2 (10 gpm/sf) and Filter 4 (12 gpm/sf) operated at their design rate.

Figure 7-45. Average UFRV for Train 1 (6 gpm/sf) and Train 2 (8 gpm/sf) both with pre-ozonation evaluated with the 10-ft head loss threshold compared to 12-ft threshold from May 18 to May 26, 2020 Bar plots represent average value with the minimum and maximum shown with brackets. Filter 1 (8 gpm/sf) operated at the filter design rate.

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In addition, Table 7-20 and Table 7-21 summarize the average UFRVs from the limited trial for the higher and lower filtration rate periods, respectively, and the percent difference between UFRVs with the 12-foot threshold compared to the 10-foot threshold. Overall, the average UFRVs for all filters, except Filter 6 at 12 gpm/sf, met the 10,000 gal/sf goal for all filtration rates when using a 12-foot threshold for terminating filter runs. In comparison, if a 10-foot threshold is used for terminating filter runs, all filters still met the performance goal of 6,500 gal/sf with the 10-foot threshold, but none of the filters’ average UFRV met the additional goal of 10,000 gal/sf.

Table 7-20. Average UFRV Train 1 (12 gpm/sf) and Train 2 (10 gpm/sf) Both with Pre-Ozonation Evaluated for 10- and 12-ft Head Loss Threshold, May 12-May 18, 2020 Filter Filtration Rate F1-Anth-60 F2-Anth-66 F3-Anth-72 F4-Anth-72 F5-Anth-66 F6-Anth-60 gpm/sf 10 10 10 12 12 12 10 ft Head loss 9,235 11,520 13,636 9,191 8,288 7,011 12 ft Head loss 11,874 14,558 17,116 12,015 10,591 9,802 % Difference between 25% 23% 23% 27% 24% 33% 12 ft and 10 ft

At the higher filtration rates, increasing the terminal head loss value from 10 feet to 12 feet increased average UFRVs between 23–33 percent.

Table 7-21. Average UFRV for Train 1 (6 gpm/sf) and Train 2 (8 gpm/sf) Both with Pre-Ozonation Evaluated With the 10-ft Head Loss Threshold Compared to 12-ft Threshold, May 18-May 26, 2020 Filter Filtration Rate F1-Anth-60 F2-Anth-66 F3-Anth-72 F4-Anth-72 F5-Anth-66 F6-Anth-60 gpm/sf 8 8 8 6 6 6 10 ft Head loss 13,857 17,678 15,040 21,899 21,179 18,495 12 ft Head loss 17,020 21,555 22,415 25,349 24,645 21,620 % Difference between 20% 20% 39% 15% 15% 16% 12 ft and 10 ft

At the lower filtration rates, increasing the head loss threshold from 10 feet to 12 feet increased average UFRVs between 20 to 39 percent at the 8 gpm/sf filtration rate, but at the 6 gpm/sf filtration rate, the average UFRVs only increased by 15 to 16 percent. Filter 3 was more challenged during this time when compared to Filter 4 because its initial CBHL was greater than Filter 4. It is hypothesized that this is the reasoning for the dip in performance of Filter 3 at 8 gpm/sf when a head loss trigger of 10 feet is used.

7.3.9.6 Organics Removal TOC reductions observed through the treatment process during the filtration rate comparison period are summarized in Table 7-22.

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Table 7-22. Average TOC Removal by Filter Design During the Filtration Rate Trial Filter Design Filtration Ratea Average TOC (mg/L)b Average Percent Removalc Raw Water 0.94 -- 6 gpm/sf 0.42 54% 60-inch 8 gpm/sf 0.45 52% (Filters 1 and 6) 10 gpm/sf 0.44 54% 12 gpm/sf 0.43 54% 8 gpm/sf 0.42 55% 66-inch 6 gpm/sf 0.42 55% (Filters 2 and 5) 10 gpm/sf 0.42 55% 12 gpm/sf 0.42 55% 6 gpm/sf 0.42 55% 72-inch 8 gpm/sf 0.42 55% (Filters 3 and 4) 10 gpm/sf 0.42 55% 12 gpm/sf 0.42 55% a. Filters operated at 10 gpm/sf and 12 gpm/sf from May 12 to May 18, and at 6 gpm/sf and 8 gpm/sf from May 18 to May 26, 2020. b. Average TOC based on two samples for each filtration rate, with the exception of Filter 4, which only had one sample for the 12 gpm/sf condition. Standard deviation varied from 0 to 0.02 mg/L for all samples. c. Average TOC removals were determined by averaging the computed daily removal of TOC between raw and individual filter effluent.

No significant difference in TOC removal was found between filters operated with different configurations and rates. During the filtration rate comparison trial, TOC was found to be consistently removed at a rate ranging from 52 to 55 percent. Reducing or increasing the filtration rates to filters did not appear to influence TOC reduction. During this period, the average raw water color was 6.7 Pt-Co, and was below the detection limit in all filter effluent samples.

7.3.10 Turbidity Spiking Filtration Performance

This section describes the filter performance observed during the turbidity spiking study performed in early June 2020, for the alum testing phases. For details regarding the logistics of the spiking study, see Section 5.7 and Section 6.6.4. For further information regarding preliminary jar testing, operational changes, as well as filtration performance for the PACl testing phase, see Appendix H.

Four filters were in service during the turbidity spiking trial: 1. Filters 1 and 6, operated at the designed filtration rate of 8 gpm/sf 2. Filters 3 and 4, operated at the designed filtration rate of 12 gpm/sf.

During both phases, Train 1 (Filters 4 and 6) was operated with intermediate ozonation, and Train 2 (Filters 1 and 3) was operated with pre-ozonation. Because Filters 2 and 5 were not operated during the study, the flow rates through the upstream treatment processes were reduced to minimize the usage rate of the spiking solution and maximize the length of the trial.

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This, in turn, increased the overall HRT of the system to 112 minutes for Train 1 and to 107 minutes for Train 2.

The initial spiking trial was conducted on June 3, 2020, with PACl testing. As discussed in Section 5.7, the settled water turbidity was elevated (around 15 NTU) and did not meet target goals. During this first attempt at introducing spiked water to the pilot, turbidity was not effectively removed during sedimentation. Because of concerns of overloading the filters, the operations team made the decision to halt operations until further jar testing was completed and a more effective coagulant approach could be developed.

Following the PACl testing and subsequent jar testing to explore alternate coagulation conditions, alum testing was initiated on June 10. Compared to the initial testing with PACl, this phase of testing was able to significantly reduce settled water turbidity, as discussed in Section 5.7.3.

Figure 7-46 shows raw, settled, and filter effluent turbidities for the period of the spiking test, including before and after the period during which raw water turbidity was elevated.

Figure 7-46. Raw, settled, and filter effluent turbidity during turbidity spiking study, alum testing

Filter effluent turbidities remained uniformly low throughout the alum testing phase. Operations were briefly interrupted during an unanticipated shut down several hours into the spiking event, but the pilot team was able to restore operations without impact to filter effluent water quality.

As described in previous sections, prior to the spiking study, it was challenging to demonstrate the potential log removal that treatment could achieve because of the low particle counts in the raw water. It is numerically impossible to demonstrate 2.5-log removal of particles if there are fewer than 316 particles/mL in the raw water, and if there are more than 1 particles/mL in the filter effluent water. The raw water particle counts need to exceed 316 particles/mL to

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demonstrate 2.5-log removal. There were many times during the pilot study when raw water particle counts were lower than this threshold, so one of the goals of the spiking trial was to increase the particles in the raw water so that the pilot could demonstrate the potential of treatment processes being evaluated.

Table 7-23 summarizes the raw water turbidity and particle counts, as well as those in the filter effluent, during the alum testing period. It is clear from these data that treatment processes that were evaluated performed beyond expectations. In all filters, turbidity remained below or at the detection limit of the instrument and particle counters (in both the 3 to 5 µm and 5 to 15 µm size ranges) remained in the low, single digits. On average, across all filters, particle removal was 3.7-logs in the 3 to 5 µm size range and 4.1-to 4.2-logs in the 5 to 15 µm size range. Overall, the treatment was robust and maintained excellent water quality throughout the duration of the spiking trial.

Table 7-23. Summary of Raw Water and Filter Effluent Turbidity and Particle Counts During the Turbidity Spiking Study, Alum Testing Sampling Location Raw Watera Parameter 50th Percentile 95th Percentile Turbidity (NTU) 19.1 22.5

Particles 3 to 5 µm 6,283 7,231 (particles/mL) 5 to 15 µm 21,056 22,732 Testing Condition Train 1: Pre-ozonationb Train 2: Intermediate- ozonationb 50th 95th Average Log 50th 95th Average Log Parameter Percentile Percentile Removalc Percentile Percentile Removalc Filter Configuration F1–Anth–60, 8 gpm/sf F6–Anth–60, 8 gpm/sf Turbidity (NTU) 0.01 0.01 -- 0.01 0.01 --

Particles 3 to 5 µm 1 2 3.7 1 2 3.7 (particles/mL) 5 to 15 µm 1 2 4.2 1 3 4.1 Filter Configuration F3–Anth–72, 12 gpm/sf F4–Anth–72, 12 gpm/sf Turbidity (NTU) 0.01 0.01 -- 0.01 0.01 --

Particles 3 to 5 µm 1 3 3.7 1 2 3.7 (particles/mL) 5 to 15 µm 1 3 4.2 1 5 4.2 a. Raw water data are based on 271 to 283 number of samples. b. Filtrate data in Trains 1 and 2 are based on 11 to 141 number of samples c. Average log removals are calculated based on averaging log removals from paired data (raw water and filter effluent for the same aliquot of water based on the HRT) when raw water particles in the indicated size range exceeded 500 particles/mL

In addition to filter effluent quality, filter productivity is an important consideration for the challenging raw water quality conditions. Even if the treatment is able to maintain good filtered water quality, if filters cannot remain in service for an acceptable length of time, then the treatment facility capacity will be limited. Because of the relatively short duration of the turbidity spiking study, a statistically significant number of runs could not be conducted to directly assess filter productivity. However, review of the filter head loss graphs from the

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spiking trial can provide insight into expected filter productivity. These curves are shown in Figure 7-47.

Figure 7-47. Filter head loss during turbidity spiking study, alum testing

The slope of the curves in Figure 7-47 indicate the rate at which head loss accumulates during the filter runs. While this rate is not constant, preliminary review of the graph from the 8 gpm/sf filter show that head loss accumulated at a rate from 0.18 to 0.25 ft/hr. Filter 3, the 12 gpm/sf filter operating with pre-ozone, had head loss accumulate rates ranging from 0.23 to 0.52 ft/hr, while Filter 4, operating at 12 gpm/sf with intermediate ozone, exhibited head loss accumulation rates from 0.21 to 0.26 ft/hr. Overall, these head loss accumulation rates were similar to, if not lower than, the rates observed under normal operating conditions throughout the duration of the pilot study.

The effect of spiking can be seen by comparing the head loss accumulation rates during the turbidity spiking study testing to the un-spiked water testing. The head loss accumulation rate of the alum testing and alum stress testing periods was generally slightly higher (lower productivity) when the spiking pump was turned off, and it returned to standard operations. The important finding though is that the head loss accumulation rates during the spiking conditions were not drastically higher than the baseline conditions, indicating that the increased pilot influent solids loading did not significantly hamper filter productivity.

Table 7-24 summarizes the UFRVs for the filters that backwashed during the study and estimates the UFRVs for the filters that did not, along with presenting the turbidity and head loss at the end of the study. All of the filters had UFRVS that surpassed 10,000 gal/sf-run.

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Overall, the filter performance was excellent and the filters handled the turbidity spike well when the coagulation process was dialed in.

Table 7-24. Filter Runs' UFRVs and Estimated UFRVs During the Turbidity Spiking Test, June 10–11, 2020 F1-Anth-60 F3-Anth-72 F4-Anth-72 F6-Anth-60 Operational Condition Pre-ozone Pre-ozone Intermediate Ozone Intermediate Ozone Filter run time, hrs > 30.3 16.4, > 14.2 24.8, > 3.4 > 28.7 UFRV, gal/sf-run > 14,600 11,800; > 10,200 17,900 > 13,800 Head loss at end of test, ft 9.1 9.7 6 7.8 Turbidity at end of test, NTU 0.01 0.01 0.01 0.01 Head loss accumulation rate 0.19-0.29 0.23-0.52 0.20-0.28 0.11-0.24

7.3.10.1 Chlorine Demand and Decay and Disinfection By-Products SDS tests were performed on select filter effluent samples collected during the turbidity spiking study. The following four filter effluent samples were disinfected and treated for corrosion control: • Filter 1 – 0.55 mg/L pre-ozonation dose • Filter 1- 1.2 mg/L pre-ozonation dose • Filter 3 – 1.2 mg/L pre-ozonation dose • Filter 4 – 1.2 mg/L intermediate ozonation dose Samples were collected over a 13-day period to evaluate DBP formation and CDD. CDD during the 13-day chloraminated period was low in all filters, ranging from 0.15 to 0.3 mg/L. Filter 4 (intermediate ozonation) had the lowest CDD of 0.15 mg/L. After a water age of 13-days, both TTHMs and HAA5s were all under 5 µg/L for all filter effluent samples, well below the water quality goals of 30 µg/L for HAA5 and 40 µg/L for TTHM. For further detail on water quality characteristics and CDD and DBP results, refer to Appendix E.

7.3.11 Biological Monitoring As discussed initially in Section 7.2.7 for the media comparison, biological monitoring during the pilot study consisted of the following standard monitoring techniques including ATP, carboxylic acids, and AOC to assess the amount of biomass and biological activity in the two pilot treatment trains.

Results presented in this section discuss the influence of filtration rate on biological activity in the filters. Biological growth, while related to the filtration rate, is actually impacted by the EBCT, which varies based on the filtration rate. The EBCT is the measure of time the water passing through a filter is in contact with the media. The range of EBCTs for the filters are summarized below in Table 7-25 by the filter media depth and filtration rate during typical operations, and during the filtration rate trial from May 16 through May 26.

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Table 7-25. Summary of Empty Bed Contact Times

a,b Filtration rate EBCT (min) (gpm/sf) 60 inch 66 inch 72 inch 6 6.2 6.9 7.5 8 4.7 5.1 5.6 10 3.7 4.1 4.5 12 3.1 3.4 3.7 a. EBCT calculated based on the filtration rate, filter cross-sectional area for a 6” filter, and the filter media depth. EBCT = (Filter Area *Depth) / Flow Rate b. EBCTs for typical operations prior to the filtration trial are bolded in the table.

7.3.11.1 Media ATP Two media ATP samples were collected after the media changeout through the end of the study. Media ATP samples from March 10 and May 12 are compared in Figure 7-48. The March 10 sample was collected after 21 days of ozone exposure with pre-ozonation operation for both trains, while the May 12 sample was collected 78 days after the start-up with new media and operation with pre-ozonation for Train 2, and 63 days for Train 1 operating with intermediate ozonation. The media samples were collected from the first sample port at the top of each filter media bed. In Filters 1, 3, 4, and 6, the first sample port is 6 to 8 inches deep into the bed, similar to all filters before the rebuild. Differently, for Filters 2 and 5, the top sample port is only 2 to 4 inches deep into the bed.

Figure 7-48. Comparison of dry (adjusted) filter media ATP on the top of the filter column, March 10-May 12, 2020 It is clear from the comparison that the length of ozone operation increased the media ATP in all filters, and most dramatically in Filters 5 and 6 over the 2-month period. ATP increased between 60,000 pg ATP/g for Filter 1 to over 190,000 pg ATP/g for Filter 5. During this time average the temperature increased by about 4 degrees (an average of 6.0°C in March to 9.6°C in May), which could have also contributed to the increase in ATP from March to May.

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There does not appear to be a trend based on filtration rate from the May sampling event. There was generally more media ATP in both trains in the 66-inch filters (10 gpm/sf), compared to the 60-inch (8 gpm/sf) and 72-inch (12 gpm/sf) filters. The 72-inch (12 gpm/sf) filters had the lowest ATP levels from the May 12 sample in both trains. The dry adjusted filter media ATP from the May 12 sample was, on average, lower in the pre- ozonation train than the intermediate ozonation train, with the pre-ozonation train ranging from 100,000 to 138,000 pg ATP/g, compared to the intermediate train ranging from 104,000 to 224,000 pg ATP/g. All three filters in Train 1 are higher than their paired filter in Train 2, suggesting some of the difference between trains for the May 12 sample could be related to the intermediate ozonation operational scheme increasing biomass growth in the filters.

7.3.11.2 AOC Removal AOC results from samples collected after the media change are presented in this section to compare AOC removal at the different filtration rates, and pre-ozonation and intermediate ozonation operation. Results from samples collected on February 26, March 18, March 24, and April 28 are compared in Figure 7-49 (after the media change), while results from June 2, collected right after the filtration rate trial, are presented in Figure 7-50. An overall statistical summary of the AOC data is presented below as well. Samples collected on April 7 and May 5, 2020, were excluded because of issues with the sample preservative. Both trains were pre-ozonated on February 26, so only Train 2 data are shown for this data. As expected, in the pre-ozonated train, AOC increased (excluding the sample from March 24) with ozonation from non-detect in the raw water to between 50 to 100 µg/L in the ozone contactor outlet, as ozonation breaks down the organic carbon in solution. A similar increase through intermediate ozonation was only observed in one of three samples. This could be a result of the nature of the AOC method, which was found to produce variable results.

Figure 7-49. AOC concentration by sample location from February, March, and April 2020

As the biological activity in the filters increased (see Figure 7-48), the AOC in the filtered water was reduced. This same trend was observed in the earlier sampling before the media changeout. Filtered water AOC ranged from less than the MRL (shown as 5 µg/L) to 98 µg/L.

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AOC was measured at the PWB distribution system entry point (Entry Point) after these sampling events to compare the existing AOC levels to the pilot. The PWB Entry Point AOC levels averaged 156 µg/L from four AOC samples taken from April 26 through June 30. All pilot filter effluent samples have observed lower AOC than the current full-scale finished water, though the pilot effluent samples were not treated with disinfection, a process that has the potential to increase AOC. In terms of the filtration rate comparison, the data are variable between sampling event and filter. During this testing period, the EBCTs were 3.7 minutes for the 72-inch media (12 gpm/sf), 4.1 minutes for the 66-inch (10 gpm/sf), and 4.7 minutes for the 60-inch filters (8 gpm/sf) (Table 7-25). On average, the pre-ozonated train’s data demonstrated increasing AOC removal with decreasing filtration rate. For some of the samples, the filters with the shortest EBCT had the highest AOC generally. On the intermediate ozone train, Filter 6 (F6-Anth-60 with the longest EBCT) had the lowest amount of AOC on average. AOC was then sampled for on June 2, 2020, prior to the start of the turbidity spiking trial, one week after the conclusion of the filtration rate comparison trial during which both trains operated with pre-ozonation. The two trains returned to operations in intermediate (Train 1) and pre-ozonation (Train 2) mode. During this time, Filters 2 and 5 were shut off to prepare for the turbidity spiking. For this sample, AOC was lower in the pre-ozonation train filter effluent, and higher AOC was observed in filters with the highest filtration rate, and shortest EBCT in both trains (Figure 7-50). Additionally, the PWB entry point continued to be higher than the unchlorinated filtered effluent.

Figure 7-50. Summary of AOC collected on June 2, 2020

The media ATP and AOC results seem to show somewhat different trends in terms of differences based on the ozonation scheme. The media ATP results from the May 12 sample indicate there may be more biomass in the intermediate train, while the AOC was slightly higher in the intermediate ozonation train for the June 2 sample (indicative of less biological activity). When reviewing the 50th percentile of the AOC data (Figure 7-51) the 50th percentiles were close between the trains, with slightly lower levels in the pre-ozonation train; 50th percentile on average was 39 µg/L with pre-ozonation, compared to the intermediate

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ozonation train with average 50th percentile of 52 µg/L. The differences between the trains are noticeable, but do not indicate a consistent difference in AOC removal with the train operation. Overall, the filter effluent AOC levels were greater than the raw water; however, the AOC concentration in the finished water were consistently reduced from the ozonated water in both trains, indicating biological activity was present.

Figure 7-51. Statistical summary of AOC data, February-June 2020

7.3.11.3 Carboxylic Acids Removal Carboxylic acid data collected after the media change are summarized in this section to compare how carboxylic acid formation and removal varied with changes in pretreatment (between intermediate ozonation and pre-ozonation and conventional filtration and direct filtration) and filtration rate. Samples collected on March 18, April 28, May 5, and June 2 are presented for the intermediate and pre-ozonation comparison, along with samples collected on May 26 for the filtration rate comparison trial. In addition to the pilot data, the PWB Entry Point was also to compare biological activity in the current finished water to the filter effluent from the pilot.

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Variation in carboxylic acids as a result of varying filtration rate (based on differences in EBCT) were consistently observed in the carboxylic acid data. Results from samples collected on March 18, April 28, and May 5, during the intermediate and pre-ozonation side-by-side comparison trial, are summarized in Figures 7-52 through 7-54. More carboxylic acid formation occurred with intermediate ozonation, resulting in greater concentrations in the filter effluent. During all three sampling events, oxalate was the most prominent carboxylic acid for both trains, similar to trends observed in past sampling. More formate was present in the filters with intermediate ozonation. As operational performance improved (based on other filter performance indices), similarly, lower carboxylic acid concentrations were measured and the difference between carboxylic acid concentrations between intermediate and pre-ozonation decreased.

Figure 7-52. Carboxylic acid concentrations measured in samples collected on March 18, 2020

Figure 7-53. Summary of carboxylic acid data collected on April 7, 2020

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Figure 7-54. Summary of carboxylic acid data collected on May 5, 2020

For the May 5 sampling event, the PWB entry point contained primarily oxalate, but also some formate, similar to the ozonated water. It appears the formate is all filtered out in the pilot system (measured as non-detect and presented as half the MRL), as no detectable formate was measured in the filter effluent. The total carboxylic acid concentration in the entry point sample was 57 µg/L, compared to the average filter effluent of 20 µg/L for Train 1 and 23 µg/L for Train 2. Based on this initial result, there are lower levels of carboxylic acid concentrations in the filter effluent compared to the PWB entry point to the distribution system. The filter effluent samples are not disinfected like the PWB entry point, so this is not a direct comparison; however, the results indicate that there is an overall improvement in biostability likely with filtration.

There appears to be a consistent trend in carboxylic acid removal with filtration rate, and thus EBCT between the filters. Carboxylic acids generally increased in the filter effluent with increasing filtration rate and shorter EBCT, as demonstrated by Filters 1 and 6 (60 inch, 8 gpm/sf) having the lowest carboxylic acids and longest EBCT (4.7 minutes), and Filters 3 and 4 (72 inch, 12 gpm/sf) with the highest carboxylic acids of the filters, and shortest EBCT (3.7 minutes). The higher carboxylic acids in filters with shorter EBCT indicate that there is likely more biological degradation occurring with longer EBCT, and therefore lower carboxylic acids in the filter effluent for Filters 1 and 6.

Figure 7-55 summarizes the carboxylic acids measured through the treatment train on May 26, when Trains 1 and 2 were both pre-ozonated at a dose of 0.55 mg/L as O3. The filtration rates were 6 gpm/sf for Train 1 filters and 8 gpm/sf for Train 2 filters. All filters were non-detect (presented as half the MRL), except Filter 1, which measured 11 µg/L of oxalate. These results, in comparison to the samples collected on May 5, suggest that the lower filtration rate improved carboxylic acid removal through the filters. Additional data points would need to be taken to confirm this finding, but it is also generally supported in the literature.

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Figure 7-55. Summary of carboxylic acid data collected on May 26, 2020, with Train 1 operating at 6 gpm/sf and Train 2 operating at 8 gpm/sf

Consistent with the PWB entry point sample from May 5, the PWB entry point total carboxylic acid on May 26 was higher (114 µg/L) than the filter effluent values, which were all non-detect, with the exception of Filter 1 (11 µg/L). This finding suggests that while carboxylic acids are generated through the ozonation process, they are lowered through the biofiltration process to lower levels than measured at the PWB entry point, and represent an improvement over the existing finished water quality. AOC analysis will be carried into SDS tests in the future to determine if the lower AOC levels observed in the filtered water persist through post-filtration disinfection and distribution.

Carboxylic acids were then sampled for on June 2, 2020, prior to the start of the turbidity spiking trial, with the two trains operating with intermediate ozonation (Train 1) and pre- ozonation (Train 2), one week after the conclusion of the filtration rate comparison trial. During this time, Filters 2 and 5 were shut off to prepare for the turbidity spiking. Results from June 6 are summarized in Figure 7-56.

Figure 7-56. Summary of carboxylic acids collected on June 2, 2020

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Based on comparison to the May 26 sample, it appears the Train 1 carboxylic acids increased when the system went back to intermediation ozonation. Carboxylic acids were notably higher in the settled water outlet and oxidation outlet (between 120 and 161 µg/L) on June 6, with a jump in the filtered effluent to between 45 and 69 µg/L, from the previous samples on May 26, indicating going back to operations at the higher filtration rate could have contributed to higher carboxylic acid, with returning Filters 3 and 4 to 12 gpm/sf and Filters 6 to 8 gpm/sf. Filter 1 operated at 8 gpm for both the May 26 and June 2 samples.

7.3.12 Chlorine Demand and Decay and Disinfection By-Products The results from the April SDS testing are summarized below for the Train 2, pre-ozonated filters, Filter 1 (F1-Anth-60) and Filter 3 (F3-Anth-72) in Tables 7-26 and 7-27, respectively, to compare CDD and DBP results at the two filtration rates, 8 gpm/sf and 12 gpm/sf. The April results indicate that there is no noticeable difference in CDD or DBPs based on filtration rate directly. The DBPs were low (<4 µg/L) in all filters following 14 days of incubation following post-filtration disinfection treatment regardless of filtration rate. Refer to Section 6.6.5 and Appendix B for more detailed results from the April SDS evaluation.

Table 7-26. SDS Test Results for CDD from April 22, 2020, by Filtration Rate CDD (mg/L) Parameter F1-Anth-60 F3-Anth-72 8 gpm/sf 12 gpm/sf CDD during 60-min free chlorine contact period 0.29 0.29 CDD during 14 day SDS period 0.21 0.23

Table 7-27. DBP Resultsa from April 22, 2020, by Filtration Rate DBP Concentrations (µg/L) DBPs F1-Anth-60, 8 gpm/sf F3-Anth-72, 12 gpm/sf TTHM 2.44 2.52 HAA5 3.20 3.20 a. Samples were treated with disinfection (free chlorine contact and secondary disinfection with chloramines) and incubated for 14 days prior to analysis.

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7.4 Filtration Summary

Review of filtration data throughout the duration of the pilot finds several trends. General observations regarding filter performance are summarized as follows:

Filter Aid • Overall, the treated Bull Run water proved to be very sensitive to filter aid dosages. A certain amount of filter aid is necessary to minimize turbidity breakthrough and to retain the particles in the filter bed; however, the rate at which head loss accumulates in the filters increases proportionally with filter aid usage. • Prior to late March 2020, there were periods when filter operations could not be optimized for all filters because a common filter aid dose was shared between the three filters on each train. Unless all three filters happened to require the same filter aid dose, one or more filters may have been receiving too high or too low of a dose, because lowering or raising the dose would have adversely impacted the operations of the other filter(s) on that train. The resulting effect of the filter aid dosing limitation is that the filters operated at higher rates generally would backwash because of turbidity breakthrough due to inadequate filter aid and the filter operated at the lower design rates would backwash on head loss because of a higher filter aid dose than needed.

Clean Bed Head Loss • In general, prior to changing out the filter media profiles, CBHL accumulated in all filters over time (i.e., decreased temperatures, insufficient backwash, or underdrain fouling). Increases in CBHL were also observed in March 2020. During April and May 2020, CBHL was relatively stable in all filters. • Over time, the GAC filters accumulated between 1 and 2 feet of CBHL that was not attributable to measured losses through the underdrains or theoretical losses through the filter media. Filter 1 was the only anthracite filter to have head losses to which a cause could not be attributed. It is thought that these unaccounted for head losses are caused by oxidizable material associated with biogrowth in the filters and underdrains. • CBHL was a limiting factor for some filters during the testing, particularly if a 10-foot terminal head loss threshold and 12 gpm/sf filtration rates were used.

Filter Media Type Comparison • Filter effluent turbidities were slightly lower in the GAC filters for the conditions tested, although the difference between the turbidities produced by the two filter media types was minimal. Either filter media was able to meet all filter effluent turbidity and particle count goals. • For all conditions tested, anthracite tended to be more productive than GAC, with higher filter UFRVs. • During pre-ozonation testing, GAC filters removed approximately 15 percent more TOC and UV254 compared to anthracite filters. However, some of this testing was conducted during a period when the adsorptive capacity of the GAC had not yet been exhausted, which would

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have contributed to organics removal across the GAC filters. Overall, organics removal was acceptable with both filter media types. • Overall, biological monitoring demonstrated more biological activity in the GAC media filters compared to anthracite, producing lower levels of AOC and carboxylic acids and higher ATP in the filtered effluent. • DBP values in disinfected SDS samples from the GAC filters were generally lower than those in the anthracite filters; however, DBP values in both were less than half of the water quality goals (<40 µg/L TTHM, <30 µg/L HAA5) indicating that both filter media types were more than capable of surpassing goals for DBP reduction.

Filtration Rate Comparison • After changing the filter media profiles to the three anthracite profiles tested, filtration rate testing indicated that there was no significant difference in filter effluent quality across the filters at all filtration rates tested. All filters produced acceptable filter effluent turbidity and low single-digit particle counts across the range of filtration rates tested. • When operated at their design filtration rate, the filters operated at 8 gpm/sf and 10 gpm/sf were more productive than the filters operated at 12 gpm/sf. • Lowering the terminal head loss threshold from 12 feet to 10 feet reduced UFRVs. Overall, the lower terminal head loss threshold reduced filter productivity by 15 to 25 percent, with reduction in productivity increasing as filtration rate increased. • When comparing filters operated at their design filtration rate, TOC removals ranged from 32 to 55 percent. UV254 reduction was similar across all filters, ranging from 77 to 81 percent, with no noticeable trend based on filter or filtration rate. Color was removed to below the MRL for all filters. • During the filtration rate comparison trial, the 60-inch anthracite filters were less productive than the other filter media profiles. However, UFRVs were consistently above productivity goals when operated at its design filtration rate of 8 gpm/sf. Performance between the 66- and 72-inch filters was comparable. • During the filtration rate comparison trial, UFRVs increased for all media designs as the filtration rate was reduced. • During the Turbidity Spiking Study, PACl Testing trial, the filters met turbidity and particle reduction goals despite being loaded with approximately 15 NTU water while receiving properly coagulated water. • During the Turbidity Spiking Study, Alum Testing trial, filter effluent quality was exceptional, with extremely low turbidities and low single-digit particle counts. The filters demonstrated greater than 3-log removal in both 3–5 µm and 5–15 µm particle size ranges. Filter productivity achieved the desired UFRV goal of 10,000 gal/sf for all filters. • As filtration rate decreases, the corresponding increase in EBCT improves the amount of AOC removal through filtration as indicated by a limited duration test. This result suggests that AOC removal during average demand flowrates may be better than observed in the pilot study.

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8.0 Summary of Pilot Plant Study Results and Findings

From July 1, 2019 through June 30, 2020, the Portland Water Bureau conducted pilot testing to support the design of the future Filtration Facility. The pretreatment ahead of granular media filtration, as well as the media selection and design criteria for granular media filtration itself has been informed based on this pilot study and a larger decision-making process.

The main objectives of the pilot study were to: • Inform treatment process selection for the Filtration Facility, • Support development of a sound, buildable, and operable basis of design for the Filtration Facility that meets regulatory requirements, • Inform design parameters and seasonal operating parameters, • Evaluate data for consistency and potential future consideration of PSW/OHA’s AWOP, and • Provide an educational tool for operators and engineers, through which they can engage in treatment process understanding.

This pilot study focused on treatment of the high-quality Bull Run Watershed source water, which is preserved through the existing watershed protection program that serves as the first barrier in a multi-barrier approach towards risk reduction and protecting water quality. Multiple treatment configurations were evaluated over the course of the pilot study. Overall, the pilot study has demonstrated that a variety of treatment options can be effective in meeting water quality objectives. The treatment trains that were evaluated have demonstrated that they can remove Cryptosporidium from the source water, and other water quality benefits have also been observed, including significantly reducing the levels of DBPs. Treatment options, such as ozone, demonstrated improvements in fine particle control in the filter effluent as well as increases in filter efficiency and productivity. Multiple high-rate granular filter media designs were shown to achieve and even surpass water quality objectives, regulatory requirements, and productivity goals.

Detailed summaries describing observations and findings for specific treatment processes are provided in the preceding sections. This section provides a general summary of the overall findings, relevant to OHA and the design, and concludes with an overall summary of the filter configurations that met the treatment requirements and performance goals.

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8.1 Coagulation, Flocculation, and Sedimentation

Four primary coagulants (alum, ferric chloride, PACl, and ACH) were evaluated during bench- and pilot-scale testing. PACl and alum both performed well at the pilot-scale in terms of filter productivity and organics removal, and offered better performance than ferric chloride and ACH under the conditions tested. PACl was used as the primary coagulant for subsequent testing because it performed as well as alum and did not require supplemental alkalinity for successful coagulation. PACl and alum were both evaluated during the turbidity spiking study, and alum produced a lower settled water turbidity and excellent filtered water quality. A coagulant was selected to make other pilot comparisons, but was not intended to define which coagulant the full-scale facility will use. For all testing except the turbidity spiking study, coagulant dosages ranged from 0.04 to 2.08 mg/L as Al3+ or Fe3+ and the PACl dose ranged from 0.1 - 1.1 mg/L as Al3+. PWB will continue to evaluate coagulants with the pilot test equipment.

Coagulant aid addition improved filtration performance during winter conditions when using PACl. Coagulant aid dose ranged between 0 and 1 mg/L.

Given the low turbidity of the Bull Run source, the majority of the coagulation conditions tested focused on charge neutralization. As expected, there was an increase in turbidity in the settled water through addition of treatment chemicals (mainly the primary coagulant) in the flocculation/sedimentation process. On average, the settled water turbidity met the pilot operational goal of ≤ 2 NTU when the source water was below 10 NTU. The source water was below 10 NTU for the entire study period, excluding the turbidity spiking study. There were a few instances where settled water exceeded 2 NTU during the pre-ozonation and intermediate ozonation test period (see Section 6.6.1), but this was also a time when some of the best filtered water quality was produced (see Section 6.6.4).

Settled water turbidity was a poor indicator of coagulation performance. Other indicators that were found to be more useful to monitor coagulation were filter water quality, filter productivity, SCM readings, and zeta potential readings. It is difficult to mimic full-scale sedimentation at pilot-scale, and performance full-scale could be better than what was experienced at the pilot-scale. The settled water turbidity was anticipated to be higher than the raw water turbidity (due to the low raw water turbidity and addition of a coagulant) and so this performance finding was as expected.

A conventional treatment process including coagulation, flocculation, sedimentation, and filtration improved filter water quality compared to direct filtration. Even though the sedimentation process did not capture the majority of solids produced at the pilot under normal operations, comparison of equivalent conditions between conventional treatment and direct filtration treatment found that filtration was more productive with sedimentation than without it at pilot scale. Both conventional treatment and direct filtration were able to meet filtered water quality goals under low turbidity raw water conditions. Filter run times were lower with direct filtration.

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The benefits of conventional treatment were evaluated through the turbidity spiking trial. Raw water turbidity was increased to approximately 20 NTU. Initially, PACl was used as the primary coagulant, which produced good filtered water quality at a charge-neutral dosing, but the settled water turbidity was higher than preferred and a settleable floc was not produced. Given this fact, the coagulant was switched to alum during the turbidity spiking trial. Alum was supplemented with sodium bicarbonate to target a pH of 7 and alkalinity around 20 mg/L as 3+ CaCO3 in the settled water. The alum dose ranged from about 1.3 to 1.7 mg/L Al and the sodium bicarbonate dose was at 33 mg/L as CaCO3. Alum in combination with sodium bicarbonate provided lower settled turbidity and approximately 75 percent of the raw water turbidity was removed through coagulation, flocculation, and sedimentation. Filtered water quality was excellent and is further described below in Section 8.3.

8.2 Oxidation

This section describes the differences observed between the oxidant type (ozone or chlorine) and feed location (pre- or intermediate ozonation) under the conditions tested. Pre-oxidation was evaluated during this study for the purposes enhancing conventional filtration and improving finished water quality; the study did not evaluate pre-oxidation for the purposes of receiving pre-filtration disinfection credit. Oxidation was determined to be an important process for maintaining particle retention in the filters compared to operation with no oxidant. In general, when no oxidant was used, increases in total particles, particles in the 3 to 5 µm size range, and particles in the 5 to 15 µm size range were observed in the filter effluent. Additionally, ozonation provided better filter productivity, and higher reduction of UV254 than operation with no-oxidant. Filtered UV254 in the pre-ozonated train was lower than with no oxidant, indicating that pre-oxidation is transforming the organics present in the raw water. Pre-ozonation significantly improved filter productivity. On average, the 50th percentile UFRVs with pre-ozonation were 1.5 times greater than the filters with no pre-oxidant.

Ozonation did produce lower levels of DBPs than pre-chlorination and filter productivity was generally higher than pre-chlorination. Overall, performance with intermediate and pre- ozonation were comparable, both ozonation modes performed well and provided effective treatment. There was little consistent difference in filter productivity between pre-ozonation and intermediate ozonation but pre-ozonation provided slightly better organics control. Pre- ozonation exhibited a higher ozone demand compared to intermediate ozonation during typical operating conditions. On average, intermediate ozone demand ranged between 0.2 and 0.5 mg/L and pre-ozonation demand ranged between about 0.4 and 0.6 mg/L. In general, these ozone demands are relatively low.

Both ozonation modes were evaluated during the turbidity spiking trial and both processes produced exceptional water quality despite the increased raw water turbidity. The difference in ozone demand between the two ozonation processes increased with increased turbidity during the spiking study. A summary of ozone demands during the turbidity spiking study are presented in Table 8-1.

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Table 8-1. Estimated Ozone Demands Ozone Demand (mg/L)a Raw Water Turbidity Turbidity Spiking Study Condition (NTU) Pre-ozonation Intermediate Ozonation (Train 2) (Train 1) PACl and coagulant aid 20 > 1.0 0.8 Alum as coagulant 20 > 1.2 0.3 Stress testing, alum as coagulant 100 > 2.3 -- a. These ozone demands are an estimation and not meant to represent absolute values.

8.3 Filtration

Through the piloting effort, filter media type, filter media effective media size, and filtration rates were assessed.

All of the filter media designs tested met turbidity performance goals at filtration rates up to their design filtration rate. The limited-duration filtration rate comparison trial found that each of the filter media profiles can meet filter effluent turbidity targets for all of the four filtration rates tested: 6, 8, 10, and 12 gpm/sf. Specifically, all the filter media designs met the turbidity goal of <0.1 NTU for 95 percent of the filter run for each of the flow rates tested: 6, 8, 10, 12 gpm/sf. Color was removed to below the MRL for all filters.

When comparing filter media type, the anthracite filters had better filter productivity, good organics removal, and are less expensive than the GAC media filters. Given these facts, all six filters were re-built in February 2020 to allow for testing of three different anthracite media profiles (two of which were identical or similar to the anthracite media profiles tested initially).

Organics removal was comparable for the anthracite filters at filtration rates of 8, 10, and 12 gpm/sf. When comparing filters operated at their design filtration rate, TOC removals (from raw water to filtered water) ranged from 32 to 55 percent, with no noticeable trend based on filter or filtration rate. The pilot filters improve the biostability of the finished water and improve finished water quality. All pilot filter effluent samples had lower AOC and lower chlorine demand and decay than the current full-scale finished water, due to filters removing material with contributions from biological activity observed on the media.

During the turbidity spiking study, the raw water turbidity was approximately 20 NTU for 30 hours comparing conventional treatment with intermediate ozonation in Train 1 and conventional treatment with pre-ozonation in Train 2. The filter effluent quality was exceptional and consistent with pilot filter effluent quality when treating unspiked raw water. Filtered water turbidities were extremely low (<0.05 NTU) and low single-digit particle counts. Filter productivity achieved the desired UFRV goal of 10,000 gal/sf for all filters.

Pilot influent particle counts increased by an order of magnitude during the turbidity spiking study compared to normal influent levels in both organism surrogate ranges. Average log removals comparing raw water to filtered water were quite high: 3.7-logs for particles of 3 to 5 µm and 4.2-logs for particles of the 5 to 15 µm size range. Comparable filter effluent quality

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was seen between the two filters tested (48 inches of 1.1 millimeter (mm) anthracite with 12 inches of 0.55 mm silica sand, and 60 inches of 1.3 mm anthracite with 12 inches of 0.65 mm silica sand).

The turbidity spiking study demonstrated the resilience of these treatment trains, as well as their ability to produce exceptional filtered water quality.

8.4 Chlorine Demand and Decay, Disinfection By- Products, and Flavor Profile Analysis

SDS testing was conducted four times (October and November of 2019 and April and June of 2020) to evaluate CDD and DBPs. DBP levels in all filtration treated water were much lower than the control samples taken from the current full-scale system (Lusted Outlet sample). DBP concentrations were lower in samples collected from the pre-ozonated filters than in samples collected from the pre-chlorinated filters. After a water age of 14 days, HAA5s were less than 6 µg/L in pre-ozonated samples and less than 14 µg/L in pre-chlorinated samples; pre-ozonated samples had half the level of TTHMs compared to pre-chlorinated samples (10 µg/L versus 20 µg/L). Comparing the filter effluent DBP concentrations of the 14-day April SDS samples to the historical May Stage 2 levels indicates that TTHM and HAA5 concentrations could be reduced significantly from present levels using conventional treatment with ozonation.

Overall, both intermediate and pre-ozonation showed improvement in terms of lower CDD compared to existing treatment during the April 2020 testing. Free chlorine demand during the primary disinfection step of the SDS test (60-minute free chlorine contact period) was 0.3 mg/L in filter effluent from all three filters tested, compared with 0.6 mg/L in the raw water and 0.5 mg/L in the Train 1 filter influent. Thus, the free chlorine demand was reduced 20 percent through pretreatment, and 50 percent by the entire treatment process. Total chlorine demand- decay was comparable between intermediate ozonation filter (Filter 4) measured to be about 0.3 mg/L compared to 0.2 mg/L for the pre-ozonated filters.

Based on the October and November SDS testing when organics are the highest, filtration reduced CDD (combination of CDD measured during the free chlorine contact period and the subsequent 14-day chloraminated SDS period) compared to the Lusted Hill Outlet sample by 50 percent. The total CDD ranged from 1.9 to 2.0 mg/L for the Lusted Hill Outlet sample compared to less than 1 mg/L total CDD exhibited by the filter effluent samples.

In November, a set of samples was sent to Seattle Public Utilities for sensory analysis, including Flavor Profile Analysis (FPA) and Flavor Rating Assessment (FRA). The five-member panel rated the filtered water to be highly acceptable as everyday drinking water, and it was given a top FRA of 1 on a scale of 1 to 9. No distinct differences were found between samples based on filter media or pre-treatment. In comparison, unfiltered, disinfected water samples collected from PWB’s system received FRA scores ranging between 1 and 4. Overall, filtration is expected to maintain or exceed customer acceptance of the water as indicated by these results.

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8.5 Design Considerations

The pilot provided a great opportunity to inform the design of the full-scale Filtration Facility. Under the charge neutralization conditions tested, it was observed that coagulation was sensitive to chemical dosing, and that small changes in coagulant and coagulant aid dosing could reduce coagulation performance. It is recommended that the coagulant and coagulant aid chemical feed systems within the Filtration Facility be designed to control chemical dosing to increments of a tenth of a mg/L, and the Filtration Facility be configured to provide supplemental alkalinity prior to coagulation.

Turbidity was not the best indicator of pretreatment for typical raw water quality. An SCM and zeta potential analyzer were very beneficial to optimize pretreatment and are therefore recommended as tools for operators to use at the future Filtration Facility. Online instrumentation was challenged by the low alkalinity, low turbidity source water. Care should be taken in selection of online analytical equipment. The pilot can continue to serve as a tool to evaluate online instrumentation through demonstration testing.

Filter aid was found to be important for controlling particle breakthrough in the filters during some seasonal conditions. While there were occasions when the filters retained particles well without filter aid, performance was inconsistent. Feeding excess filter aid will increase the rate at which head loss develops in the filters, so filter aid usage must balance particle control and head loss accumulation rate. Due to equipment limitations, the lowest filter aid dose tested during this pilot study was 0.008 mg/L, at which point particles were still well controlled. The minimum filter aid feed dose at which point particles are not well controlled was not determined during this study. It is recommended that filter aid storage and feed facilities be included in the design of the Filtration Facility with the capability to control dosage to the thousandth of a mg/L (0.001 mg/L) and turndown the dose to at least as low as 0.008 mg/L.

The pilot primarily evaluated a terminal head loss of 12 feet. Managing head loss accumulation rates is particularly important if a lower terminal head loss threshold is selected. While testing found that the filters could meet productivity goals at a terminal head loss threshold of 10 feet, lowering the terminal head loss threshold from 12 feet to 10 feet reduced filter productivity by 15 to 33 percent.

Filter CBHL increased over time and required more vigorous backwashes and chlorine soaks periodically. Increases in CBHL appeared to be related to oxidizable material in the underdrain, additional biogrowth, and/or higher-than-necessary doses of filter aid. The pilot underdrains are not what will be installed full-scale so this may be an area where the pilot performance will vary from full-scale. Regardless, the ability to dose a high chlorine residual in the backwash is recommended for filter maintenance should the need arise.

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8.6 Regulatory Considerations for OHA

This Report fulfills the Bilateral Compliance Agreement (OHA 2017) requirement for a pilot study. This Report presents documentation to request approval for high filtration rates exceeding 6 gpm/sf for deep bed (>60-inch media) filters. Multiple filter configurations were tested for their ability to meet turbidity standards equivalent to water produced by standard filter loading rates. Tested filter configurations are summarized in Table 8-2 below. The highest filtration loading rate for which each filter configuration was demonstrated to meet effluent turbidity criteria are shown. Additionally, the highest loading rate for which each configuration met other criteria, including particle count removal and unit filter run volumes, are also shown. Based on Cryptosporidium levels, the Bull Run source is considered Bin 1 classification based on source water monitoring results, and therefore, no additional treatment is required for filtered systems.

It is requested that each of the conventional filtration configurations listed below be approved at the designated filtration loading rate for providing 2.5-log removal for Giardia and 2-log removal for Cryptosporidium. The specific configuration that will be implemented in the future Filtration Facility will be recommended subsequently in future design reports and plans.

Additional credits (if needed due to a change of bin classification) can be granted for watershed control programs and combined filter performance and individual filter performance through the LT2 Rule. A 0.5-log credit for Cryptosporidium removal can be granted for a state approved watershed control program. It is expected that the current watershed protection program will continue after installation of the full-scale Filtration Facility, and this additional credit could be leveraged if needed in the future. An additional 0.5-log credit (for a total of 1.0-log credits) for Cryptosporidium can be granted if individual filter effluent is less than 0.15 NTU in at least 95 percent of measurements in each month in each filter and 0.3 NTU is never exceeded. This study has demonstrated that filtration can consistently produce filter effluent that is less than 0.1 NTU. Therefore, these additional credits could be explored if needed in the future.

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Table 8-2. Filter Media Designs for OHA Approval Filter media configurations Anth-60 Anth-60 Anth-66 Anth-72 GAC-60 GAC-72 Performance assessment Proposed approval filtration rate 8a 8b 10a 12c 8b 12d Maximum filtration rate tested that 12e 8 12e 12 8 12 achieved desired turbidity goal Maximum filtration rate that 10e 8 12e 12 8 12 achieved desired UFRV goal Top layer filter media design Media type Anthracite Anthracite Anthracite Anthracite GAC GAC Depth (in.) 48 48 54 60 48 60 Effective size (mm) 1.05 – 1.15 1.15 – 1.25 1.15 – 1.25 1.25 – 1.35 1.25 – 1.35 1.25 – 1.35 Bottom layer filter media design Media type Silica Sand Silica Sand Silica Sand Silica Sand Silica Sand Silica Sand Depth (in.) 12 12 12 12 12 12 Effective size (mm) 0.50 – 0.60 0.55 – 0.65 0.55 – 0.65 0.60 – 0.70 0.50 – 0.60 0.50 – 0.60 Total Filter Media Design L/d ratio 1,660 1,520 1,650 1,640 1,490 1,730 Total depth (in.) 60 60 66 72 60 72 a. Proposed approval filtration rate is based on data presented in Sections 6.6.5, 7.3.2, 7.3.3, and 7.3.9. b. Proposed approval filtration rate is based on data presented in Sections 6.3.2, 6.5.2, and Appendix F. c. Proposed approval filtration rate is based on data presented in Sections 6.3.2, 6.5.2, 7.2.2, 7.3.2, 7.3.3, 7.3.9, and Appendix F. d. Proposed approval filtration rate is based on data presented in Sections 6.3.2, 6.5.2, 7.2.2, 7.3.2, and Appendix F. e. Filtration rates evaluated during filtration rate comparison trial.

Direct filtration options are not being considered at this time for the full-scale Filtration Facility. However, the pilot results demonstrate that such a process configuration meets filter effluent water quality goals under low turbidity raw water conditions.

This Report documents benefits and explores options for including oxidants in the treatment train. Ozonation is studied in this report as pretreatment to enhance other processes. No credit for pre-filtration disinfection is being requested at this time. The specific oxidants and location within the process train will be proposed in subsequent design documentation.

Finished water disinfection demand and decay and DBPs were investigated with this study. A specific final disinfection approach will be proposed in subsequent design documentation. Subsequent bench-scale corrosion control and coupon studies are currently being undertaken. Results and requests for approval on corrosion control will be submitted separately.

Portland Water Bureau 8-8 Brown and Caldwell

9.0 References

American Water Works Association (AWWA).1999. Water Quality and Treatment. McGraw-Hill, 5th edition, page 16.10. Association of State Drinking Water Administration (ASDWA). 2016. Area Wide Optimization Program (AWOP) Compliance Assistance Through Optimization. https://www.asdwa.org/wp-content/uploads/2016/07/AWOP-Exec-Summary_revised03-04-14.pdf BC (Brown and Caldwell). 2020. Project Definition Report, Bull Run Treatment Projects–Filtration. October, 2020. BC. 2019. 2019 Pilot Plant Work Plan. Prepared for PWB. Revised May 2019. Crittenden, J.C., Montgomery Watson Harza (firm). 2012. MWH’s Water Treatment: Principles and Design, 3rd Edition, 3rd ed. John Wiley & Sons, Hoboken, New Jersey. Evans, P.J., J.L. Smith, M.W. LeChevallier, O.D. Schneider, L.A. Weinrich, and P.K. Jjemba. 2013. A Monitoring and Control Toolbox for Biological Filtration (No. 4231b). Water Research Foundation, Denver, Colorado. Gong, B., J.K. Edzwald, T. Tran, and J. Kim. 1993. Pilot Plant Comparison of Dissolved Air Flotation and Direct Filtration. In Proc. of the AWWA Annual Conference, Denver, Colo.: American Water Works Association. Hooper, J., Alito, C., Vickstrom, K., Evans, P., Black, S., Lauderdale, C. 2019. Guidance Manual for Monitoring Biological Filtration of Drinking Water (No. 4620). Water Research Foundation, Denver, Colorado. Huck, P.M., B.M. Coffey, A. Amirtharajah, and E.J. Bower. 2000. Optimizing Filtration in Biological Filters (No. 252). AWWA Research Foundation, Denver, Colorado. Keithley, S.E. & Kirisits, M.J. 2018. An Improved Protocol for Extracting Extracellular Polymeric Substances from Granular Filter Media. Water Res., 129:419-427. Keithley, S.E. & Kirisits, M.J. 2019. Enzyme-Identified Phosphorus Limitation Linked to More Rapid Headloss Accumulation in Drinking Water Biofilters. Environ Sci Technol., 53(4):2027-2035. Kirisits, M., Venu, I.S., Gallo, C., and Palmer, E. 2020. Report for EPS, biofilm morphology, and enzyme activity. Prepared by the University of Texas at Austin for Brown and Caldwell. February 2020. LeChevallier, MW and Norton, WD. 1992. Examining Relationships Between Particle Counts and Giardia, Cryptosporidium, and Turbidity, Journal AWWA. December. Page 54–60. OHA (Oregon Health Authority). 2017. Bilateral Compliance Agreement between the Oregon Health Authority and the Portland Water Bureau. December 18, 2017. PSW (Partnership for Safe Water). 2014. Guidelines for Phase IV Application for the “Excellence in Water Treatment” Award. https://www.awwa.org/Portals/0/files/resources/water%20utility%20management/partnership%20safe%20water/f iles/p4guidelines%20Dec%2014_Final.pdf Yorton, R.A., W. Bellamy, J.K. Edzwald, S. Braun, and T. Tran. 1993. Particle Counting for Evaluating Treatment of Low- turbidity Waters. In Proc. Of the AWWA Annual Conference. Denver, Colo.: American Water Works Association.

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