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Nestle USA, Inc.—Ripon, CA January 28, 2011 <br /> 2011 Revised Feasibility Study <br /> In general, pump-and-treat removes mass in the dissolved phase, but may not <br /> effectively remove COCs adsorbed to saturated soil within a timeframe that is <br /> acceptable to project stakeholders and oversight agencies. The effectiveness of <br /> mass removal depends on various soil and chemical properties such as soil type, <br /> organic carbon content, water solubility, soil to water partitioning, etc. Organic <br /> chemicals with low aqueous solubilities tend to exist in a state of equilibrium <br /> between the dissolved phase and the soil-adsorbed phase, favoring soil <br /> adsorption. Groundwater extraction by pump-and-treat is able to remove organic <br /> chemicals which are present as a dissolved phase. As the impacted water is <br /> removed from the pore space, clean water (i.e. water without COCs) enters the <br /> pore space, a portion of the organic chemicals present desorbs from the soil <br /> matrix and dissolves into the clean water, and the process continues. This <br /> process is slow, requiring long-term operation to effectively remove or reduce <br /> COC impacts. After a pump-and-treat operation stops, groundwater is no longer <br /> being actively removed from the treatment area and COC concentrations may <br /> rebound due to desorption of COCs that are less-dilute when groundwater <br /> velocities diminish towards ambient conditions. <br /> During 2007 and 2008, the Nestle pump-and-treat system at the Site extracted <br /> approximately 127.5 million gallons of water and removed 148 pounds of CDCs. <br /> This is equivalent to 1.17 pounds per million gallons (PMG) of water extracted. <br /> Figure 5 shows the mass removal trend and the volume of water removed during <br /> operation of extraction wells EU-3 and EU-4 through 2008. As shown in the <br /> figure, the amount of COCs removed has declined significantly since the pump- <br /> and-treat system started. Initially the mass removal rate was 26.9 PMG and has <br /> declined to a rate of 1.17 PMG"v"'. This data indicates that pump-and-treat is <br /> most effective when it is initiated. As time passes, pump-and-treat becomes less <br /> efficient in removing COCs. COC removal efficiency may be improved by pulsed <br /> operation, more focused extraction, or other design enhancements. <br /> Pump-and-treat can effectively control plume migration with proper design, but is <br /> slow and mass reduction diminishes over time. This technology may eventually <br /> remove sufficient mass but will take a long time to do so. <br /> 9.2.1.2 Implementability <br /> Pump-and-treat technology has been employed at the Site since 1987. <br /> However, long-term operation and maintenance (O&M) of extraction wells and <br /> treatment systems pose significant challenges. <br /> The treated effluent water requires appropriate disposal and/or reuse. Current <br /> options for treated effluent include discharge to the storm sewer, to the sanitary <br /> sewer, or to the non-potable water line operated by the City. The WWTP <br /> lagoons cannot accept larger volumes from the extraction systems; therefore, <br /> this limitation must be considered for future applications of this technology. <br /> Extracted groundwater must be treated prior to disposal or reuse. Treatment <br /> requirements depend on the concentrations of COCs present in the water, other <br /> water quality issues and the quantity of groundwater being treated. The <br /> 25 <br />