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The performance and VOC removal rates of the Stockton Avenue extraction and treatment <br /> system have declined since 200742, suggesting that source mass has been remediated. Nestle <br /> installed three groundwater monitoring wells (M-52B, M-53B, and M-54C) in the vicinity of the <br /> Off-site groundwater extraction and treatment system in December 2009 <br /> • to monitor post-remedial groundwater conditions, <br /> • to confirm the lack of significant VOC concentrations beneath the Stockton Avenue <br /> area, and <br /> • to confirm that VOCs detected in this area are predominately related to migration from <br /> the City of Ripon sewage treatment ponds near the Stanislaus River. <br /> Groundwater samples collected from the three monitoring wells indicate <br /> • that the Stockton Avenue Treatment System has successfully remediated the target <br /> area surrounding this location, and <br /> • support the findings of Site Conceptual Model" that there is no Intermediate Aquifer <br /> source of COCs beneath the area of 519 South Stockton Avenue43 <br /> Nestle requested permission to shut down the Off-site groundwater extraction and treatment <br /> system44. The RWQCB concurred 45 and ECM ceased system operation on October 1, 2010. <br /> In December 2007, ECM installed two new groundwater extraction wells (EU-3 and EU-4) at <br /> Industrial Avenue location (the On-Site location). These new wells were installed to more <br /> precisely target the On-Site COC concentration for source removal and hydraulic control to <br /> prevent or limit migration. Extraction from wells EW-1 and EI-1 ceased in February 2008, once <br /> EU-3 and EU-4 commenced pumping. A complete discussion of the IRAP groundwater <br /> extraction and treatment system, which began operation in February 2008, can be found in the <br /> Interim Remedial Action Plan, Well Installation and Aquifer Test Report46 and the Interim <br /> Remedial Action Plan Groundwater Extraction System Startup Report47 <br /> In December 2009, ECM decommissioned eight VE wells (VE-1 through VE-3, VE-5 through VE-7, <br /> VE-9, and VE-10) that were located at the former Nestle facility at 230 Industrial Avenue. A ninth <br /> VE well (VE-8)was decommissioned at the property located at 519 South Stockton Avenue. <br /> ECM resumed extraction from well EI-1 on October 29, 2010, as a result of the M-10A <br /> investigation, to target mass removal and provide containment in the "lower A zone" (100 feet — <br /> 115 feet bgs) of the Upper Aquifer. <br />