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Mr. Cervantes <br /> 16 October 2012 <br /> Page 4 <br /> Confirmation Soil Vapor Sampling <br /> As discussed with the CVRWQCB, an additional round of soil vapor confirmation samples will <br /> be collected from the high PCE concentration areas after SVE system optimization testing is <br /> complete. Soil vapor samples will be collected using procedures consistent with previous soil <br /> vapor sampling events conducted at the Site to ensure comparable data. <br /> Prior to sampling, Geosyntec will procure all drilling permits required by the San Joaquin <br /> County Environmental Health Department and clear proposed drilling locations with a private <br /> utility locator. Soil gas sampling will be conducted in general accordance with the California <br /> Environmental Protection Agency (CaIEPA), Department of Toxic Substances Control (DTSC) <br /> "Draft Advisory—Active Soil Gas Investigation" dated March 2010 (CaIEPA 2010). Consistent <br /> with the May 2010 and May 2012 sampling events, leak testing will be conducted using 1,1- <br /> difluoroethane as the leak detection compound. <br /> Initial confirmation soil vapor samples will be collected from locations adjacent to SG-1, SG-3, <br /> and SG-4 due to the presence of PCE in exceedance of the commercial CHHSL during the May <br /> 20112 sampling event. The temporary sample points will be advanced by TEG (Rancho Cordova, <br /> CA) using direct-push technology (StrataprobeTM), and soil-gas samples will be collected from <br /> depths of approximately 5 feet bgs at each location. Soil gas samples will be analyzed for PCE <br /> using Modified EPA Method 8260B by the TEG-operated mobile laboratory to allow real-time <br /> data collection. If the concentrations in these locations at the 5 feet bgs exceed the CHHSL for <br /> PCE, step out borings will be advanced adjacent to buildings in these areas to confirm that PCE <br /> concentrations next to the buildings are below the CHHSL. Soil vapor samples will not be <br /> collected below 5 feet bgs because the objective of the assessment is to assess the potential for <br /> vapor intrusion. <br /> Soil Closure Request <br /> Following completion of the SVE system optimization and the confirmation soil vapor sampling, <br /> Geosyntec will prepare a closure request for on-Site soil. The request will summarize the SVE <br /> system optimization testing procedures, evaluate its operational performance and the expected <br /> benefit of continued operation of the SVE system verses the additional costs; summarize the <br /> rebound and optimization test results; summarize the confirmation soil vapor sampling results; <br /> evaluate risk associated with remaining PCE concentration in soil vapor (if necessary); and <br /> recommend closure of on-Site soil as appropriate. We anticipate that prior to preparing the <br /> formal request, a meeting will be held with the CVRWQCB to review the system optimization <br /> 20121000-SVE Optimization and Confinnation Testing <br /> engineers I scientists I innovators <br />