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s <br /> 1.0 Background <br /> 1.1 Introduction <br /> This Evaluation Monitoring Program (EMP)work plan was prepared to further assess the nature <br /> and extent of the release from the Corral Hollow Sanitary Landfill (CHSL) in response to the <br /> California Regional Water Quality Control Board, Central Valley Region, (RWQCB) letter dated <br /> February 5, 2007. The letter requested that a work plan be prepared to investigate potential off <br /> site migration of landfill gas in the vadose zone and VOCs and chloride in groundwater from <br /> CHSL. This work plan is also in accordance with requirements of the California Code of <br /> Regulations Title 27, Section 20425. <br /> 1.2 Site Description <br /> The CHSL is a closed, unlined Class III landfill located at 31130 South Corral Hollow Road, in <br /> southern San Joaquin County, approximately 5 miles south of the City of Tracy, at the <br /> intersection of Interstate 580 and Corral Hollow Road(Figure 1). The landfill covers <br /> approximately 58 acres, of which 43 acres was permitted disposal area. The remaining area is <br /> comprised of access roads, storm water retention ponds, setbacks for environmental monitoring, <br /> and firebreaks. Land within 1,000 feet of the facility is used for grazing and agriculture. <br /> The landfill ceased receiving waste in 1991. A final cover was constructed in the fall of 1995. <br /> The closure cover consists of a 2 to 6-foot foundation layer under a 1-foot minimum thick, low- <br /> permeability soil layer, with a 1-foot thick vegetative surface layer. A landfill gas (LFG) <br /> collection system was installed and began operating in December 2001 as corrective action(see <br /> below). <br /> 1.3 Compliance History <br /> Volatile organic compounds (VOCs, Trichlorofluoromethane and Tetrachloroethene)were first <br /> detected in groundwater samples collected from MW-5 (shallow aquifer) during the fourth <br /> quarter of 1991. Confirmation samples were collected in February 1992 and the presence of <br /> VOCs at monitoring well MW-5 was confirmed. The presence of VOCs in MW-5 was due to <br /> landfill gas influence. In addition, relatively high detections of VOCs have observed in vadose <br /> zone gas well GW-2 (Figure 2). <br /> A corrective action plan(CAP), which included the closure and final cover construction for the <br /> landfill, was implemented in 1995. The LFG control and collection system has been in operation <br /> Corral Hollow EMP WP.DOC 1.1 February 28,2007 <br />