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1 <br /> 2.0 BACKGROUND <br /> The CHSL is a closed, Class III municipal solid waste disposal facility located southeast of <br /> the intersection of Corral Hollow Road and State Route 580 at 31130 South Corral <br /> Hollow Road in San Joaquin County, California (Figure 1). The site ceased operations in <br /> 1991, and was formally closed with construction of a prescriptive final cover system in <br /> 1995. <br /> Groundwater monitoringat the CHSL began in 1987 with the installation of wells MW-1 <br /> g <br /> 1 through MW-5 as part of the Solid Waste Assessment Test (SWAT) program. Through <br /> construction of these wells, two water-bearing zones were identified: a shallow zone <br /> that is limited to the northern third of the site, and a deeper zone that underlies the <br /> entire site. <br /> 1 <br /> In 1991, VOCs, including trichlorofluoromethane and tetrachloroethene, were detected <br /> in samples from shallow groundwater monitoring well MW-5. The detections were <br /> verified during subsequent monitoring events, and the presence of VOCs has historically <br /> been attributed to minor landfill gas migration. In response to these detections, the <br /> County installed a landfill gas collection and destruction system at the site in 2001. <br /> Currently, groundwater at the site is monitored by network of six monitoring wells: <br /> Wells MW-4, MW-5, MW-8, and SB-1 monitor a shallow aquifer. Wells MW-6 and <br /> MW-7 monitor a deeper aquifer. <br /> 3.0 SITE SETTING <br /> The following sections provide the site setting and include a description of the site <br /> physiographic and climatic conditions in the vicinity of the CHSL, and the geology and <br /> hydrogeology underlying the CHSL. <br /> 3.1 PHYSIOGRAPHIC AND CLIMATIC SETTING <br /> 3.1.1 Landfill Location <br /> The CHSL is located in southern San Joaquin County, south of the City of Tracy (Figure 1). <br /> The site address is 31130 Corral Hollow Road, and the landfill is situated southeast of <br /> the intersection of Corral Hollow Road and State Route 580. The site occupies a portion <br /> of Section 18 in Township 3 South, Range 5 East of the Mount Diablo Baseline and <br /> Meridian system. <br /> Physiographically, the site is located on the northeastern flank of the Diablo Range at <br /> the transition to the San Joaquin Valley. The site is bounded by Corral Hollow Creek on <br /> its eastern side and Corral Hollow Road on its western side. <br /> EMP Report—Phase II Geo-Logic Page ■ 2 <br /> Corral Hollow Sanitary Landfill ASSOCIATES <br /> August 21,2012 <br />