1191 Second Ave, Suite 630 Seattle, WA 98101 206-652-4905 206-652-4927 (Fax City of Longview Mint Farm Regional Water Treatment Plant Preliminary Design Report Part 1 Basis of Design Report March 2010 Prepared for City of Longview 1525 Broadway Street Longview, WA 98632 K/J Project No.0997003*00 Table of Contents List of Tables ................................................................................................................................ vi List of Figures.............................................................................................................................. vii List of Appendices ....................................................................................................................... vii Section 1: Introduction ............................................................................... 1-1 1.1 Authorization ....................................................................................... 1-1 1.2 Project Description .............................................................................. 1-1 1.3 Purpose of Report ............................................................................... 1-2 1.4 Abbreviations ...................................................................................... 1-2 Section 2: Water Quality and Treatment Objectives ................................. 2-1 2.1 Water Quality ...................................................................................... 2-1 2.2 Treatment Objectives .......................................................................... 2-2 2.3 Pretreatment Assessment ................................................................... 2-2 2.3.1 Oxidation .................................................................................. 2-2 2.3.2 Pre-Treatment for Arsenic Removal ......................................... 2-3 2.4 Granular Media Pilot Study ................................................................. 2-3 2.4.1 Pilot Study Protocol .................................................................. 2-3 2.4.1.1 Introduction and Purpose ....................................... 2-3 2.4.1.2 Preliminary Oxidant Demand Testing .................... 2-4 2.4.1.3 Pilot Study Equipment............................................ 2-4 2.4.1.4 Backwash Protocol ................................................ 2-5 2.4.1.5 Backwash Water Settling Tests ............................. 2-5 2.4.1.6 Pilot Study Operations ........................................... 2-5 2.4.1.7 Raw Water Characterization .................................. 2-5 2.4.1.8 Pilot Study Sampling and Analysis ........................ 2-5 2.4.2 Pilot Study Results and Conclusions ....................................... 2-7 2.4.2.1 Operational Parameters ......................................... 2-7 2.4.2.2 Removal of Target Inorganic Contaminants .......... 2-8 2.4.2.3 Filter Run Time ...................................................... 2-9 2.4.2.4 Disinfection By-Products in the Treated Water .... 2-11 2.4.2.5 Backwash Water Settling Tests ........................... 2-11 2.4.2.6 Conclusions and Recommendations ................... 2-12 Section 3: Filtration Alternatives Evaluation ............................................. 3-1 3.1 Alternatives Evaluation Process .......................................................... 3-1 3.1.1 Project Stakeholders ................................................................ 3-1 3.1.2 Feasible Filtration Alternatives ................................................. 3-1 3.1.3 Evaluation Criteria .................................................................... 3-2 3.1.4 Stakeholder Preparation .......................................................... 3-2 City of Longview – Mint Farm RWTP Part 1 Basis of Design Report Part 1, Page i y:\projects\09proj\0997003.00_longview\09. reports\9.11 predesign report\march 2010\part 1_basis of design_3-5-10.doc Table of Contents (cont’d) 3.1.5 Alternatives Evaluation Workshop ........................................... 3-3 3.2 Evaluation Criteria and Weighting ....................................................... 3-3 3.2.1 Weighting Matrix ...................................................................... 3-4 3.3 Filtration Alternatives ........................................................................... 3-5 3.3.1 Greensand Granular Media Filtration ....................................... 3-5 3.3.1.1 Pretreatment .......................................................... 3-5 3.3.1.2 Ancillary Equipment and Systems ......................... 3-5 3.3.1.3 Capacity ................................................................. 3-6 3.3.1.4 Evaluation .............................................................. 3-6 3.3.2 Membrane Filtration ................................................................. 3-7 3.3.2.1 Pretreatment .......................................................... 3-7 3.3.2.2 Ancillary Equipment and Systems ......................... 3-7 3.3.2.3 Capacity ................................................................. 3-7 3.3.2.4 Evaluation .............................................................. 3-8 3.3.3 Rehabilitate the Existing Treatment Plant ................................ 3-9 3.3.3.1 Key Elements in Repair and Rehabilitation ............ 3-9 3.3.4 Alternatives Cost Comparison .................................................. 3-9 3.3.4.1 Comparative Capital Construction Costs ............... 3-9 3.3.4.2 Capital and Net Present Value Costs for Repair and Rehabilitation of the Existing RWTP .................................................................. 3-11 3.3.4.3 Comparative Net Present Value Costs ................ 3-13 3.4 Evaluation of Filtration Alternatives ................................................... 3-14 3.4.1 Evaluation Matrix .................................................................... 3-14 3.5 Selected Filtration Alternative ............................................................ 3-15 Section 4: Water Treatment Plant Process Design Elements ................... 4-1 4.1 Water Treatment Plant Basis of Design .............................................. 4-1 4.1.1 Water System Demand Projections ......................................... 4-1 4.1.2 Design Criteria Summary ......................................................... 4-1 4.2 Greensand Filters ................................................................................ 4-2 4.2.1 Filter Design Summary ............................................................. 4-2 4.2.2 Air Scour Blowers ..................................................................... 4-2 4.3 Oxidation Alternatives ......................................................................... 4-2 4.3.1 Constituents Exerting Oxidant Demand ................................... 4-2 4.3.2 Alternative Oxidation Chemicals .............................................. 4-3 4.3.2.1 Aeration ................................................................. 4-3 4.3.2.2 Chlorine ................................................................. 4-4 4.3.2.3 Potassium Permanganate ..................................... 4-5 4.3.2.4 Ozone .................................................................... 4-5 4.3.3 Oxidation Alternative Recommendation ................................... 4-5 4.3.4 Hypochlorite Storage and Metering System Design Summary ................................................................................. 4-6 4.4 Fluoridation ......................................................................................... 4-6 City of Longview – Mint Farm RWTP Part 1 Basis of Design Report Part 1, Page ii y:\projects\09proj\0997003.00_longview\09. reports\9.11 predesign report\march 2010\part 1_basis of design_3-5-10.doc Table of Contents (cont’d) 4.4.1 Sodium Fluoride ....................................................................... 4-7 4.4.2 Fluorosilicic Acid ...................................................................... 4-8 4.4.3 Fluoridation Alternative Recommendation ............................... 4-8 4.4.4 Fluoridation Storage and Metering System Design Summary ................................................................................. 4-9 4.5 Corrosion Control and pH Adjustment ................................................. 4-9 4.5.1 Sodium Hydroxide Storage and Metering System Design Summary ............................................................................... 4-10 4.6 Backwash Water Recovery Alternatives ........................................... 4-11 4.6.1 Backwash Quantities .............................................................. 4-11 4.6.2 Backwash Water Handling ..................................................... 4-11 4.6.2.1 Backwash Water Infiltration Basin Disposal System ................................................................. 4-12 4.6.2.2 Discharge to the Sewer........................................ 4-12 4.6.2.3 Backwash Water Recovery System ..................... 4-12 4.6.3 Backwash Water Recovery System Recommendation .......... 4-14 4.7 Waste Solids Handling and Dewatering Alternatives ........................ 4-14 4.7.1 Backwash Waste Solids Quantities ........................................ 4-14 4.7.2 Waste Solids Handling and Dewatering Alternatives ............. 4-15 4.7.2.1 Thickening Lagoons/Drying Beds ........................ 4-15 4.7.2.2 Mechanical Dewatering and Solids Storage Tank ....................................................................