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Stockton Avenue Groundwater Extraction System Shutdown Request July 7, 2010 <br /> Former Nestle USA, Inc. Facility, Ripon, CA <br /> An evaluation of the data collected from M-54C and other area monitoring wells, as well as an <br /> evaluation of historic data trends in the Intermediate Aquifer wells between the City of Ripon <br /> sewage treatment ponds and Stockton Avenue, yields the following conclusions: <br /> 1. As illustrated in Figure 3, groundwater flows north-northwest, away from the City of Ripon <br /> sewage treatment ponds, towards the Stockton Avenue site. Also shown in Figure 3 is <br /> the historical percolation trench, where the City of Ripon reportedly disposed of industrial <br /> waste water that likely contained TCE. Aside from the historical sewer line leak that has <br /> impacted the B-zone (discussed earlier and below), the percolation trench is the only <br /> suspected source for CDCs that is upgradient of well E-6. Therefore, it is reasonable to <br /> conclude the source for CDCs in groundwater captured by well E-6 would be the historical <br /> percolation trench. Further evidence provided below strongly indicates that the City of <br /> Ripon sewage treatment ponds are the source for COC-affected groundwater captured by <br /> well E-6, not the aforementioned sewer line leak. <br /> 2. As illustrated in Figure 3, the relative distribution of COC concentrations in wells near the <br /> City of Ripon sewage treatment ponds is similar to the distribution of COC concentrations <br /> observed in extraction well E-6, but very different from the chemical signature associated <br /> with the sewer line leak that historically impacted the shallow water table aquifer2. Based <br /> on these similar chemical signatures, and because the lagoons are a known source for <br /> COCs and are located hydraulically upgradient of E-6, it is evident that the origin of CDCs <br /> in groundwater captured by well E-6 is coming from the lagoons, and not from a release <br /> near the Stockton Avenue site where no source has been identified in the Intermediate <br /> aquifer. <br /> 3. Pumping at well E-6 would be expected to increase the northward hydraulic gradient <br /> between the easternmost portion of the City of Ripon sewage treatment ponds where <br /> higher COC concentrations are present in groundwater, particularly vinyl chloride. This <br /> increased hydraulic gradient has promoted the migration of CDCs in the Intermediate <br /> Aquifer from the area beneath the treatment ponds towards E-6. This is illustrated in <br /> Figure 4, where the vinyl chloride molar fraction in M-8C1 has intermittently increased with <br /> time until 2004, when a sharp and consistent increase in vinyl chloride is observed after <br /> pumping commenced at well E-6 in July 2004. <br /> The trends and evaluation of data illustrated in Figure 3 and Figure 4 support that the lagoons <br /> are the source for COCs observed in groundwater samples from the Intermediate Aquifer near <br /> Stockton Avenue and that well E-6 has not been an effective remedy for COC-affected <br /> groundwater in the Intermediate Aquifer. The continued operation of the system would be very <br /> energy intensive yet have no apparent environmental benefit. Therefore, ECM requests RWQCB <br /> concurrence to cease extraction from well E-6. <br /> 2 Historical B-zone well data from M-813 (Figure 1 and Figure 2) indicate that the chemical signature associated <br /> with the sewer line release is primarily TCE. <br /> 3 This is the area where City of Ripon historically discharged industrial wastewater,as shown in Figure 3. <br /> 3 <br />