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Monitoring Well Installation Report April 15, 2010 <br /> Former Nestle USA, Inc. Facility, Ripon, CA <br /> TCE and other CDCs have been sufficiently reduced to justify shutdown of the <br /> Stockton Avenue Treatment System. The discrete groundwater samples <br /> collected from wells M-52B and M-53B indicate the presence of low levels of <br /> TCE and cis-1,2-DCE, consistent with other B-Zone wells in the vicinity of the <br /> 519 South Stockton Avenue Site (Table 5). These data also indicate that the <br /> Stockton Avenue Treatment System has been successfully remediating the <br /> target area surrounding this location. Therefore, ECM recommends permanently <br /> shutting down the Stockton Avenue System. Details of the proposed shutdown <br /> will be documented under separate cover. <br /> In order to confirm the conclusion, ECM recommends a quarterly sampling <br /> frequency for wells M-52B and M-53B for the first year. A revised monitoring <br /> frequency will be recommended after an evaluation of the first year of data is <br /> completed. <br /> • The purpose of installing well MW-54C was to verify and monitor potential <br /> upgradient migration of CDCs emanating from the City of Ripon municipal waste <br /> water treatment lagoons. Analysis of sampling results from this well and the <br /> comparison (Figure 9) of COC concentrations in wells M-20C1, M-17C1, M-8C1 <br /> agree with Site Conceptual Mode14 conclusion that the presence of COCs in the <br /> Intermediate Aquifer under Stockton Avenue is primarily from migration of COCs <br /> emanating from the municipal lagoon area. This migration has been taking place <br /> due to mounding at the lagoon area, the natural northwest gradient of the <br /> regional groundwater flow, and uncontrolled pumping by municipal and private <br /> wells. These observations also support the findings of Site Conceptual Mode14 <br /> that there is no Intermediate Aquifer source of COCs beneath the area of 519 <br /> South Stockton Avenue. Therefore, the operation of extraction well E-6 is not <br /> necessary. ECM recommends a quarterly sampling frequency for M-54C for the <br /> first year in order to monitor seasonal trends and variations. A revised monitoring <br /> frequency may be recommended after an evaluation of the first year of data is <br /> completed. <br /> 10 <br />