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hydrocarbon contaminated soil, and asbestos). WMU-A covers about 8 acres where designated wastes and hazardous waste sludge were placed from the late 1970s through 1984. In accordance with regulatory approved plans, WMU-A was closed and capped in 1989. Semi-annual post-closure monitoring for WMU-A is performed in accordance with permit requirements issued by the Department of Toxic Substance Control (DTSC). Quarterly monitoring for the entire landfill parcel is also performed in accordance with RWQCB Waste Discharge Requirement (WDR) Order No. 97-141. 1.3 GEOLOGIC & HYDROGEOLGC OVERVIEW The geology and hydrogeology of the FSL have been detailed in several reports including Kleinfelder&Associates (1991, 1997, 1999), CH2MHil1 (1992), and Beta Associates (1988). These studies have confirmed that site geologic and hydrogeologic conditions are consistent with regional conditions. 1 The Forward Sanitary Landfill is located approximately 7 miles southeast of Stockton, California, near the center of the Great Valley Geomorphic Province. This portion of the Great Valley is underlain by more than 8000 feet of marine and non-marine sediments that were derived by weathering of the Sierra Nevada to the east, and the Central Coast Ranges to the west. The uppermost non-marine sedimentary unit at the site is the poorly consolidated Victor Formation. This unit is typically heterogeneous, and laterally and vertically discontinuous, consistent with a fluvial depositional environment. The Victor Formation is about 100 feet thick, generally coarse-grained, but contains moderate quantities of silts and clays near the site. No Holocene faults have been mapped near the property. Boring log data collected at the site indicate that the Victor Formation may be subdivided into three major subunits in this area: A) From the surface to a depth of approximately 28 to 40 feet: highly interbedded orange-brown(oxidized) sandy silt, clayey silt, silt, clay, with few fine sand stringers. B) From about 30-40 feet deep to 55-75 feet deep (25 to 35 feet thick): interbedded gray- brown sand, silty, sand, and clay. C) From 55-75 feet deep to about 100-110 feet(35 to 45 feet thick): light- to yellow- brown fine- to medium-grained sand, silty sand, and some coarse-grained or gravelly layers. Groundwater is typically encountered at the FSL at depths ranging from approximately 70 to 80 feet below the ground surface, near the top of the "C" subunit of the Victor Formation. The groundwater flow gradient at the site averages about 0.003 ft/ft to the north and northeast, in agreement with regional flow patterns. Using the aquifer hydraulic conductivity values determined in slug and bail tests completed at the site (2 x 10-2 to 2 x 10-3 cm/sec), and an estimated effective porosity of 0.2, the groundwater velocity near the FSL is estimated to be approximately 0.082 to 0.82 feet per day. 2 Geologic Associates