Ice Pigging Report
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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 2 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) 3 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 4 solids would be expected to lower chlorine demand/decay reactions, thereby enhancing the City’s ability to improve ORP conditions over time.