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• <br />r (I Backgrounj <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, and reflecting comments received in a letter dated March 13, 2007. The <br />February 5, 2007 letter requested that a work plan be prepared to investigate potential off site <br />migration of landfill gas in the vadose zone and VOCs and chloride in groundwater from CHSL. <br />This work plan is also in accordance with requirements of the California Code of Regulations <br />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 is located in <br />Township 3 South, Range 5 East of Section 18 on the Mount Diablo Meridian. It 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 />Corral Hollow EMP WPlan Rev2Mar 22-07.DOC 1-1 March 20, 2007 <br />