Kirt Ervin – 4-February-2014 To: Utility Service Group Date: Melinda Friedman, Andrew Hill, Stephen From: Booth, and Michael Hallett– Project: Ice Pigging Demonstration at City of Longview, WA Confluence Engineering Group, LLC
Cc: Amy Blain, Jeff Cameron, City of Longview Subject: Summary of Results
BACKGROUND In January 2013 the City of Longview (City) started up the new Mint Farm Regional Water Treatment Plant (MFRWTP), which treats groundwater supplied by four production wells. The treated groundwater replaces the surface water supply, which was in use for approximately 67 years and formerly treated at the plant on Fishers Lane. Approximately 30 days after the source changeover, the City began experiencing water quality problems in the area served by the Baltimore Street main between Oregon Way and 22nd Avenue and has received taste, odor, and color complaints from residents in that area. The majority of pipe in this area is old, unlined cast iron with significant tuberculation. Due to the source changeover, the accumulated pipe scales and tubercles have been undergoing a re-equilibration process resulting from changes in water chemistry, flow direction, and increased water age.
The City contracted with Utility Services Group (USG) to conduct a week of ice pigging trials on five parallel water mains between Baltimore Street and Nichols Boulevard. The City had contracted independently with Confluence to evaluate the effectiveness of flushing practices in the area. Subsequently, USG contracted with Confluence to conduct an independent review of ice pigging by conducting monitoring for a variety of inor- ganic, organic, and microbial parameters over the profile of one ice pigging run.
It is important to note that the application of ice pigging at the City of Longview was not intended to “solve” a legacy metals or biofilm accumulation problem, as might be the case for application at other water systems. As mentioned above, the City of Longview is experiencing an ongoing pipe scale destabilization problem, resulting in the continued release of accumulated materials from the pipe scale into the bulk water. Re-equi- libration to the new water chemistry and flow conditions could take many months. The City was eager to implement a main cleaning technique that could remove the destabilized materials from the distribution system, thereby reducing the total solids load that could be delivered to customers, without further destabi- lizing the fragile scales through aggressive physical disruptions (such as would occur with swabbing or pig- ging). Thus, continued water quality problems are therefore expected in the regions that were ice pigged, until the distribution system scale re-stabilizes, despite removal of undesirable constituents that had accu- mulated in the water mains.
SAMPLING APPROACH Confluence arrived on site on July 29, 2013 to profile ice pigging operations along 19th Avenue and Baltimore. Approximately 2,000 feet of 6-inch and 8-inch pipe were cleaned. Table 1 summarizes the sampling plan that was implemented by Confluence. Ambient background samples were collected from the discharge hydrant, before and after pigging, and at various times during the pig. The sampling plan was developed so as to maximize understanding of the ice pig profile while trying to conserve labor resources and laboratory costs. Thus, not all parameters were analyzed at all time steps. A map of the area is shown in Attachment A.
Sampling was also conducted by Confluence during a flushing event on July 18th, 2013 from a hydrant at 20th Avenue and Baltimore. Unfortunately, the City was not able to achieve high velocities during this flush, so sampling represented more of a bulk water turnover, not high velocity unidirectional flushing (UDF). Thus, an “apples-to-apples” comparison of high velocity UDF vs. ice pigging was not able to be performed as origi- nally intended.
Table 1. Summary of Ice Pigging Sampling Plan Measured Group Parameter Before After During Total On Site/Field General Temperature* 1 1 6 8 pH 1 1 2 4 Turbidity* 1 1 2 ORP 1 1 6 8 Alkalinity 1 1 2 TDS 1 1 6 8 Disinfection Cl2 Residual (free) 1 1 3 5 Cl2 Residual (total) 1 1 3 5 Ammonia 1 1 1 3 Solids Apparent Color 1 1 6 8 True Color 1 1 6 8 Metals Fe (Total) 1 1 6 8 Fe (Dissolved) 1 1 3 5 Mn (Total) 1 1 6 8 Mn (Dissolved) 1 1 3 5 Commercial Lab** Nitrite 1 1 1 3 Nitrate 1 1 1 3 Disinfection TOC 1 1 3 5 Solids TSS* 0 Metals ICP Metals**, Total (all 0 samples) and dissolved (1 ice sample) 1 1 3 5 Microbial Sulfur bacteria Iron bacteria HPC (R2A)** 1 1 3 5 * Measured by USG: Temperature, turbidity, conductivity, sediment mass removed ** ALS Analytical in Kelso Before: Ambient water prior to pigging After: Ambient water after pigging During Ice Sampling: Begin sampling ice after the conductivity alarm (to be notified by USG) Sample at following times (min): 1, 2, 4, 6, 8, 12
ICE PIGGING RESULTS As shown in the following figures and tables, ice pigging removed considerable quantities of material from the distribution system. Approximately 67 pounds of dried solids were removed from this 2,000-foot stretch of main, which extrapolates to 177 pounds of solids per mile. The inorganic, organic, and microbial content of this material is summarized below. Approximately 37% of the dried solids composition was directly ac- counted for with the analyses conducted, with the majority of the mass comprised of metals. The remaining
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unmeasured fraction is likely comprised of the oxide, oxyhydroxide, carbonate, and sulfate groups that com- prise the chemical precipitates, along with nutrients, additional cations and anions, and soluble metal spe- cies. The majority of material was removed within the first one to four minutes after the ice arrived at the dis- charge hydrant. For many of the parameters, contaminant removal decreased by an order of magnitude after 8 minutes. Attachment A provides additional information collected by Confluence and USG during the pigging operation.
Metals Removal
As summarized in Table 2, the selected metals shown account for approximately 37% of the total mass of material removed. Iron dominated by far, representing 34% of the total mass removed. Approximately 23 pounds of iron was removed from this stretch of pipe, which extrapolates to approximately 60 pounds of iron per mile of unlined cast iron pipe in the Baltimore Street area. Profiles for selected metals are shown in the Figures below, and additional metals profiles are shown in Attachment A.
Table 2. Summary of Selected Metals Removal Rates Mass Removed Percent
Metal (lb) (lb/mile) (g) (g/mile) (%)(a) Iron 22.8 60.2 10,344 27,309 34 Aluminum 1.07 2.83 486.1 1,283 1.6 Manga- nese 0.4 1.1 192.2 507.3 0.6 Zinc 0.152 0.401 68.9 182 0.2 Copper 0.03 0.0845 14.5 38.3 0.04 Barium 0.0172 0.0454 7.8 20.6 0.03 Lead 0.01 0.026 4.5 11.9 0.01 Arsenic 0.003 0.009 1.5 3.9 0.00 Total 24.5 64.7 11,120 29,356 36.5 (a) Percentage of overall dried solids mass removed during the trial (67 lb)
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Iron Manganese 10,000,000 100,000 37,200 1,500,000 1,490,000 24,000 1,000,000 202,000 10,000 3,170 100,000 2,500 8,090 5,250 1,000 161 10,000 241 530 119 104 1,000 238
µg/L (log scale) (log µg/L 100 65 µg/L (log scale) (log µg/L 100 10 10
1 1 Before 1 min 4 min 8 min After Before 1 min 4 min 8 min After
Iron, Dissolved Iron, Total Manganese, Dissolved Manganese, Total
Lead Arsenic 1,000 664 402 400 277 338 350 100 300 250
10 2.51 200 164 µg/L
µg/L (log scale) (log µg/L 150 0.73 1 100 50 22 1 4 0 1 2 0 0 Before 1 min 4 min 8 min After Before 1 min 4 min 8 min After
Lead, Total Arsenic, Dissolved Arsenic, Total
Physical Parameters
Although a direct “apples-to-apples” comparison with unidirectional flushing was not possible due to limita- tions in flushing velocities that could be achieved in this region, it should be noted that the maximum appar- ent color achieved during flushing operations conducted a week prior to ice pigging was 95 color units – similar to background water quality conditions during the destabilization event. Higher color would have been expected with a high velocity unidirectional flush.
Measurements of oxidation reduction potential (ORP) show that conditions were very low/negative before, during, and after ice pigging operations. The ORP leaving the plant is currently in the 600-800 range, although ORP levels at the time of destabilization were not known, but were likely in the 200-400 range, based on available disinfectant residual information. The nearly complete loss of oxidizing conditions demonstrates the magnitude of chlorine demand and decay reactions occurring due to release of soluble iron, manganese, biofilm, and other constituents from the pipe surface. Low and negative ORP conditions propagate soluble releases associated with scale destabilization. Ice pigging alone would not be expected to increase the ORP of the bulk water reaching the site, unless all upstream pipes had already been cleaned and ongoing chlorine demand/decay reactions were under control. As shown in the figure below, the ORP of the water reaching the site was still negative after ice pigging. Nonetheless, removal of such significant quantities of accumulated
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solids would be expected to lower chlorine demand/decay reactions, thereby enhancing the City’s ability to improve ORP conditions over time.
Turbidity measurements were taken by USG throughout the ice pigging operation and are shown in Attach- ment A. The ice causes scatter with the online turbidity analyzer, which maxes out at approximately 400 NTU. Therefore a single sample collected at T=4 minutes was sent to the laboratory for analysis. A reading of 3,860 NTU was obtained.
Apparent Color Oxidation Reduction Potential
40,000 150 121 34800 115 116 35,000 100 30,000 50 25,000 0
20,000 ORP(mV) Before 1 min 4 min 8 min After 15,000 -50
10,000 7700 Color Units Color -100 5,000 1900 -98.5 -96.8 142 190 0 -150 Before 1 min 4 min 8 min After
Organics and Microbial Removal
Total organic carbon levels were profiled across the ice pig, as were heterotrophic bacteria, iron related bac- teria, and sulfur bacteria (see results below). Approximately 0.17 pounds of organic carbon were removed from the system, extrapolating to 0.44 pounds per mile of pipe. Very high levels of heterotrophic bacteria were removed, with counts increasing by two orders-of-magnitude relative to baseline. The ice pig process resulted in improved microbial conditions in the bulk water afterwards. Likewise, iron-related bacteria were present in the range of 500-9,000 cfu/mL prior to ice pigging, and quickly dropped off to approximately 500 cfu/mL within the first minute of ice pigging. Sulfate reducing bacteria were not detected before, during, or after this ice pigging trial.
Total Organic Carbon Heterotrophic Plate Count 25 100,000 42,000
20 20 10,000 3,650 2,050 950 15 1,000 335
mg/L 10 100 5 5 scale) (log cfu/mL 2 1 1 10 0 Before 1 min 4 min 8 min After 1 Before 1 min 4 min 8 min After
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Iron Related Sample Bacteria Sulfur Bacteria (CFU/mL) (CFU/mL) Before Approx 500-9000 Approx- Not aggressive bacteria 1 Min Approx 25-500 Absent 4 Min Approx 500 Absent/Not aggressive 8 Min Approx 500 Absent/Not aggressive After Approx 500 Absent
Visual Comparison of Pipe Condition “Before” and “After” Ice Pigging
The City of Longview pulled sections of pipe before and after ice pigging. The degree of scale destabilization is visible in the “before” section, where tubercles have broken off/dissolved down to the pipe surface in some areas. It is interesting and encouraging to note that despite the pounds of iron and other materials removed from the system during ice pigging, there is no apparent visual disturbance to the pipe tubercles as a result of the ice pigging process. It is very important to avoid physically damaging the tubercles since they serve as massive reservoirs of soluble iron, sulfides, and other constituents that can cause on-going water quality impacts such as chlorine demand, discoloration, taste, odor, etc.
Before Ice Pigging After Ice Pigging
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CONCLUSIONS
Ice pigging at the City of Longview removed 67 pounds of material from a 2,000 foot stretch of pri- marily 6-inch unlined cast iron pipe. This material was comprised primarily of iron (34 wt%), as would be expected. Large quantities of other metals (both regulated and unregulated) were also removed from the sys- tem. Significant quantities of organic material and bacteria were also removed, resulting in improved mi- crobial conditions in the bulk water after ice pigging compared to pre-pig conditions. Although more aggressive than unidirectional flushing, ice pigging did not appear to disrupt existing tubercles, allowing for rapid recovery of the system post-pigging. However, the City made several pinhole leak repairs following ice pigging, which may have removed accumulated materials that were masking existing leaks. Significantly greater masses of accumulated materials were removed by ice pigging compared to unidirectional flushing, especially within this flow-constricted section of the distribution system. All though the City obviously benefited from the removal of 67 pounds of material from this stretch of distribution system main, long-term water quality improvements were not observed after ice pigging or unidirectional flushing. This is likely because the distribution system had not yet stabi- lized, so additional accumulated materials continued to solubilize and be released after cleaning.
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Attachment A JOB RECORD/REPORT/SUMMARY
JOB INFORMATION: Client City of Longview Date 29‐Jul‐13 Location Balt / 19th Insertion Point 19th Ave Discharge Point B / 03 Pipe Length 2000 Lft Pipe Diameter 8 & 6" GIS Material CI Usage Domest Water Distribution Volume of Ice 1100 Gallons Ice Fraction 90% Total Water Used 12936 Gallons
ONSITE PROCEDURE: Pre‐Clean Readings Immediate Post‐Clean Readings Change Turbidity (NTU) 5 Turbidity (NTU) 4.7 ‐0.3 Temperature (ᵒF) 69.3 Temperature (ᵒF) 65.1 ‐4.2 Pressure (PSI) 13.7 Pressure (PSI) 14 0.3 Conductivity (mS/cm) 0.5 Conductivity (mS/cm) 0.6 0.1 Timeline: Arrive Main Isolated by Client Main Opened Ice out Main Returned to Service
Pre‐clean Readings Ice in Conductivity Alarm Post‐clean Readings Leave Site
Comments:
Maximum Flow Rate (gpm) 403 Lowest Temperature Reached (ᵒF) 25.0 Ambient Air Temperature (°F) 75
RESULTS SUMMARY:
GRAPH JOB RECORD/REPORT/SUMMARY
SEDIMENT DATA: # Time (s) Flow Rate (gal/m) Temperature (°F) Conductivity (mS/cm) Sample Mass (g)Sed. Mass (g/gal) Sediment (lb/gal)
24052.9633 1 60 333.33 50.1 23.9 0.41 1093.32 2.405 17034.0482 2 90 200.82 25.9 42.5 0.80 1285.22 2.827 32010.7291 3 150 209.60 25.3 47.0 1.38 2313.98 5.091 46927.1961 4 210 222.21 25.0 50.5 1.80 3199.79 7.040 136583.622 5 270 320.39 27.7 40.7 2.52 6459.11 14.210 125228.506 6 330 372.42 36.2 8.3 1.71 5094.75 11.208 137716.008 7 390 380.66 51.4 3.6 1.80 5481.53 12.059 30734.4394 8 450 396.64 56.8 2.4 0.37 1174.05 2.583 30091.1454 9 510 403.52 59.5 5.3 0.35 1129.86 2.486 26141.4801 10 570 399.64 62.2 1.2 0.31 991.10 2.180 18504.9119 11 630 399.13 63.3 0.8 0.22 702.47 1.545 10112.2718 12 690 399.50 63.9 0.7 0.12 383.52 0.844 8416.83618 13 750 399.26 64.1 0.7 0.10 319.41 0.703 7513.39806 14 810 397.63 64.1 0.6 0.09 286.29 0.630 6711.69206 15 870 398.62 64.3 0.6 0.08 255.11 0.561 4983.83428 16 930 396.63 64.3 0.6 0.06 190.38 0.419 940.970256 17 990 243.73 64.2 0.6 0.03 58.50 0.129 0.0340232 18 1050 1.27 64.2 0.6 0.04 0.41 0.001 2.05301396 19 1080 11.38 64.1 0.5 0.03 2.73 0.006 20 21 22 23 24 25 26 27 28 29 0.0 30 0.0 #VALUE! 31 #VALUE! 32 #VALUE! 33 #VALUE! 34 #VALUE! 35 #VALUE! 36 #VALUE! 37 #VALUE! 38 #VALUE! 39 #VALUE! 40
RESULT: Sediment Removed (lb)66.93 Sediment Removed per mile (lb) 176.99 The above values are calculated from samples taken every 60 seconds on site. For each sample the flow rate, and the sediment densities are assumed to remain constant within that 60 second period. From this we can calculate the total amount of water/ice and therefore can estimate the total mass of sediment over the sampling period
PHOTO
Summary of Ice Pigging Parameter Profiles
Aluminum Aluminum 80,000 74,300 74,300 100,000 54,200 70,000 8,000 60,000 10,000 54,200 50,000
1,000 40,000 µg/L 30,000 100 µg/L (log scale) (log µg/L 22 20,000 8,000 10 10,000 22 0 1 Before 1 min 4 min 8 min After Before 1 min 4 min 8 min After
Aluminum, Dissolved Aluminum, Total Aluminum, Dissolved Aluminum, Total
Arsenic Apparent Color 400 40,000 338 34800 350 35,000 300 30,000 250 25,000
200 164 20,000 µg/L 150 15,000 100 10,000 7700 Color Units Color
50 22 5,000 1900 1 4 0 1 2 142 190 0 0 Before 1 min 4 min 8 min After Before 1 min 4 min 8 min After
Arsenic, Dissolved Arsenic, Total
Barium Barium 1,800 1,710 10,000 1,600 1,710 1,400 811 1,000 1,200 185 180
1,000 811 100
µg/L 800 16 600 scale) (log µg/L 10 10 7 6 400 185 180 200 7 16 6 10 0 1 Before 1 min 4 min 8 min After Before 1 min 4 min 8 min After
Barium, Dissolved Barium, Total Barium, Dissolved Barium, Total
Cadmium 120
100 96
80
60 µg/L 40 27
20 9 0 0 1 0 0 0 Before 1 min 4 min 8 min After
Cadmium, Dissolved Cadmium, Total
1 Total Organic Carbon 25
20 20
15
mg/L 10
5 5 2 1 1 0 Before 1 min 4 min 8 min After
Chromium 80 70 70 63 60 50
40 µg/L 30 20 11 10 0 0 0 0 1 0 Before 1 min 4 min 8 min After
Chromium, Dissolved Chromium, Total
Copper Copper 3,000 10,000 2,480 2,480 1,820 2,500 1,000
355 2,000 1,820 97 100
1,500 13 12 µg/L 10
1,000 scale) (log µg/L 2 1 500 355 1 1 13 97 2 12 0 0 Before 1 min 4 min 8 min After Before 1 min 4 min 8 min After
Copper, Dissolved Copper, Total Copper, Dissolved Copper, Total
Heterotrophic Plate Count Heterotrophic Plate Count 45,000 42,000 100,000 42,000 40,000
35,000 10,000 3,650 2,050 30,000 950 1,000 25,000 335 20,000 cfu/mL 100 15,000 cfu/mL (log scale) (log cfu/mL 10,000 3,650 10 5,000 2,050 950 335 0 1 Before 1 min 4 min 8 min After Before 1 min 4 min 8 min After
2 Iron Iron 1,600,000 1,500,000 1,490,000 10,000,000 1,500,000 1,490,000 1,400,000 1,000,000 202,000 1,200,000 100,000 1,000,000 8,090 10,000 5,250
800,000 530 µg/L 1,000 238 600,000 65 µg/L (log scale) (log µg/L 100 400,000 202,000 200,000 8,090 10 238 5,250 530 65 0 1 Before 1 min 4 min 8 min After Before 1 min 4 min 8 min After
Iron, Dissolved Iron, Total Iron, Dissolved Iron, Total
Iron-Related Bacteria - Reported Range
10,000 9,000 9,000 8,000 Minimum of Range Detected 7,000 Maximum of Range Detected
6,000 Approximate Number Detected 5,000 4,000 CFU/mL 3,000 2,000 500 500 500 500 500 1,000 25 0 Before 1 min 4 min 8 min After
Lead Lead 664 1,000 664 700 402 277 600
100 500 402
400 10 2.51 277 µg/L 300 µg/L (log scale) (log µg/L 0.73 200 1 100 2.51 0 0.73 0.05 0 0 0 Before 1 min 4 min 8 min After Before 1 min 4 min 8 min After
Lead, Dissolved Lead, Total Lead, Total
Manganese Manganese 40,000 37,200 100,000 37,200 24,000 35,000
10,000 30,000 2,500 3,170 24,000 25,000 1,000 161
241 20,000 119 104 µg/L
µg/L (log scale)(log µg/L 100 15,000 10,000 10 5,000 2,500 3,170 161 119 241 104 0 1 Before 1 min 4 min 8 min After Before 1 min 4 min 8 min After
Manganese, Dissolved Manganese, Total Manganese, Dissolved Manganese, Total
3 Nickel Oxidation Reduction Potential 140 132 150 115 116 121 120 100
100 50
80 68 0 ORP (mV) ORP µg/L 60 Before 1 min 4 min 8 min After -50 40
20 9 14 3 -100 1 2 2 -98.5 -96.8 0 -150 Before 1 min 4 min 8 min After
Nickel, Dissolved Nickel, Total
Sodium Sodium 15,200,000 15,200,000 100,000,000 16,000,000 13,500,000 13,500,000 12,100,000 5,150,000 14,000,000 10,000,000 12,100,000 1,000,000 89,400 12,000,000 16,100 91,800 100,000 10,000,000 15,600
8,000,000 10,000 µg/L 6,000,000 5,150,000 1,000 µg/L (log scale) (log µg/L 4,000,000 100 2,000,000 16,100 89,400 10 15,600 91,800 0 1 Before 1 min 4 min 8 min After Before 1 min 4 min 8 min After
Sodium, Dissolved Sodium, Total Sodium, Dissolved Sodium, Total
Thallium Turbidity 4,500 3.0 2.7 3860 4,000 2.5 3,500
2.0 3,000
2,500 1.5
µg/L 2,000
Turbidity (NTU) Turbidity 1,500 1.0 0.6 1,000 0.5 0.0 0.0 327 367 0.0 500 0.0 0.1 0.0 13.2 12.9 0.0 0 Before 1 min 4 min 8 min After Before 1 min 4 min 8 min After
Thallium, Dissolved Thallium, Total
Zinc Zinc 16,000 14,600 100,000 14,600 14,000 6,670 10,000 12,000 2,170
10,000 1,000
190 6,670 8,000 61 49 µg/L 6,000 100 µg/L (log scale) (log µg/L 4,000 9 8 2,170 10 49 2,000 61 190 9 8 0 1 Before 1 min 4 min 8 min After Before 1 min 4 min 8 min After
Zinc, Dissolved Zinc, Total Zinc, Dissolved Zinc, Total
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