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1.1 Purpose <br />This work plan presents the procedures to install two new groundwater monitoring well <br />(MW -8, MW -9) at Corral Hollow Sanitary Landfill (CHSL). <br />1.2 Site Description <br />CHSL is a closed, unlined Class III landfill located at 31130 South Corral Hollow Road, <br />in southern San Joaquin County, approximately 5 miles south of the City of Tracy, at <br />the intersection of Interstate 580 and Corral Hollow Road (Figure 1). The landfill <br />covers approximately 58 acres, of which 43 acres was permitted disposal area. The <br />remaining area is comprised of access roads, storm water retention ponds, setbacks <br />for environmental monitoring, and firebreaks. Land within 1,000 feet of the facility is <br />used for grazing and agriculture. The landfill ceased receiving waste in 1991. <br />Currently the landfill is under post closure maintenance. <br />A petroleum pipeline is present in the access road on the northeast side of the <br />property. <br />1.3 Geology and Hydrogeology <br />Surface soils at the site are typically sands and gravels to a depth of about 70 feet, <br />underlain by low permeability silts and clays to 150 feet. Sands and gravels <br />predominate to a depth of approximately 430 feet. Highly impermeable sandy clays <br />are present at 430 feet. <br />The hydrogeology at the site is complex. A deep aquifer is found at an elevation of <br />approximately -45 to -57 feet (MSL), at a depth of between approximately 299 and 357 <br />below the surface. Groundwater flows in the deep aquifer to the northeast. <br />A shallow aquifer is found beneath the northeast and east side of the landfill property <br />due to the presence of the Corcoran Formation, which rises from the northeast, <br />apparently intercepting the landfill base. This aquifer is unconfined, and mounds near <br />monitoring well SB -1. The elevation of this shallow aquifer is approximately 230 feet <br />MSL. Depth to this shallow aquifer varies between 12 and 65 feet below existing <br />grade (depth variations result from variations in the surface elevations). Attempts to <br />locate and monitor the shallow aquifer south and east of the landfill footprint in 2003 <br />indicated that this aquifer is inconsistent in elevation, and discontinuous within the <br />landfill property. <br />The Corcoran Formation, and the associated shallow aquifer, is not found beneath the <br />southwest side of the landfill. <br />Work Plan —Groundwater Monitoring Well Installation 3 San Joaquin County <br />Corral Hollow Sanitary Landfill Public Works/Solid Waste <br />