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GEOMATRIX disposal facility. After Simplot cleaned out the tanks in 1988, the sump pump connection was 1 changed to an aboveground pipe that transfers the stormwater to another part of the facility and ultimately to the Lathrop facility lined ponds located just east of Howland Road. 2.5 Area Hydrogeology Except where locally graded, the area ground surface drains toward the southwest. Soil in the Lathrop facility area consists of alluvial deposits of the San Joaquin and Stanislaus Rivers, Delhi Fane sands, Dinuba fine sandy loams and Fresno fine sandy loams with varying permeabilities from ' rapid to moderate (SCS, 1951). The California Department of Water Resources (DWR, 1967) indicates that the surficial, recent ' alluvial sediments in the Lathrop area are underlain by the Victor formation. The Victor formation comprises coarse-grained materials much like the surficial alluvium. The surficial 1 alluvium and the Victor formation reportedly extend from the surface to about 150 feet below ground surface (bgs) in the Lathrop area. In 1964, groundwater in the Lathrop area was at about 15 feet bgs or at an elevation of 0 feet above mean sea level. DWR suggested that area pumping ' has drawn down water levels allowing sea water incursion from the San Joaquin River delta. The U. S. Geological Survey (USGS, 1981) indicates that groundwater in San Joaquin County is used for municipal, industrial, and agricultural water needs. Groundwater in western San Joaquin County,which is from marine sediments of the Coast range, is of poorer quality than groundwater ' in eastern San Joaquin County, which is from igneous sediments of the Sierra Nevada range. This is manifested by a chloride plume that was characterized as 100 to 250 mg/Q in the Lathrop area. ' USGS also found that"Agricultural practices also appear to have affected the groundwater quality as demonstrated by greater-than-average concentrations of nitrate and total dissolved solids." ' The San Joaquin County Flood Control and Water Conservation District (FCWCD, 1991) reported that groundwater in the Lathrop area was at a depth of about 20 feet bgs and flowed to ' the north/northwest. Shallow groundwater below the Lathrop facility occurs at a depth of about 10 to 15 feet bgs and ' flows generally to the southwest (RWQCB, 1994). Shallow groundwater is of fair mineral quality g Y with total dissolved solids ranging from about 800 to 1,000 mg/Q. However, shallow groundwater ' has been found to contain detectable pesticides and is currently being remediated by OXY using a pump and treat method (TreaTek, 1992). Shallow groundwater below most of the Lathrop facility contained measurable concentration of DBCP, EDB, and/or sulfolane at the start of groundwater remediation in 1982. Shallow groundwater is currently being extracted via 7 extrac- tion wells. The extracted groundwater is then treated using activated carbon to removed DBCP 5