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i w. 2.4.2 LOCAL GEOLOGY Based on logs of borings drilled by Caltrans adjacent to the site, the upper 60 feet of soil below the site consist predominately of clayey silt. Thin fine sandy interbeds occur sporadically. Groundwater was not encountered at depths of 60 feet in November 1988. Borings drilled at two sites along Fremont Avenue, approximately 1/2 mile west and 1/2 mile northeast of the Disco site, encountered similar materials to depths of 50 to 60 feet below ground surface (bgs). Silty sands were encountered between 60 and 70 feet, bgs. 4, 2.43 GROUNDWATER OCCURRENCE At the former Chevron site at the intersection of Fremont Street and Windsor Avenue, -� groundwater was first encountered at about 40 feet bgs in a silty clay (EA, 1990). Based on water level measurements and estimated groundwater gradients (EA, 1990), it appears that this water may have been perched above the water table. A stable water table was encountered approximately 70 feet bgs in a sand. At the Apache Plastics site(2050 East Fremont Street), groundwater was first encoun- tered in a sand about 63 feet bgs. (Western Geologic Resources, 1989). �., Groundwater maps produced by the San Joaquin County Flood Control and Water Conservation District (SJCFCWCD) (Spring 1990) suggest that water may be encoun- tered at a depth•of about.70 feet bgs in the area of Plant 33. Ixr 2.4.4 GROUNDWATER FLOW Plant 33 is located within an area where groundwater is extensively developed by high- capacity wells. Nearly all of these wells are several hundred feet deep and pump water from sands and gravels below about 200 feet bgs. The large withdrawals fromthese � - depths have created an extensive cone of depression, shown on the S.TCr"C -. . s ` Lateral groundwater flow in this area is often controlled by the lorations of the n a t pumping wells. Water levels in wells at the Apache Plastics and Chevron sites alolig Fremont Street suggest generally southwestward flow in late 1950.At the Plant 33 loca`• tion, flow directions may be affected by the three Del Monte process water wells,,,. located near the intersection of North Filbert Street and East Miner Avenue, that to- gether pump approximately 2,000 gal/min (Del Monte,personal communication 1991). Groundwater flow is therefore expected to be generally to the north or northwestward at the Disco site and to the west at the East Miner Avenue site. SFO3IW41WY1006.51 2-6