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i Chevron U.S.A., Inc. December 20, 1991 02310 1883 a', Page 3 hydrocarbons as gasoline(TPH-G) by U.S. Environmental Protection Agency {EPA)-approved methods 5030/8020/801 5. One soil sample was analyzed for total lead by SW-846 method 6010. 4.0 SITE CONDITIONS 4.1 HYDROGEOLOGY The site is located in the northern part of the San Joaquin Valley at an elevation of approximately 25 feet. The vai1,y fill consists of late Mesozoic through Eocene dominantly marine deposits overlain by late Tertiary and Quaternary dominantly non-marine deposits which usually contain fresh water. In Stockton area, the late Cenozoic deposits are approximately 3,000 feet thick and generally consist of alluvial gravel, sand, silt, and clay. Groundwater in these alluvial deposits is usually unconfined to semiconfined. Extensive PI i o-Pleistocene lacustrine deposits, including the diatomaceous Corcoran Clay, occur in San Joaquin Valley, south of Stockto.i. The water beneath the clay bed is usually confined. The materials penetrated to a depth of 70 feet during drilling at the site are dominantly clays with lenses of sand and silt. Tha rYvbter..tablb 1--is declined approximately 30 feet over a period of three Veale from 01metely`40466t•"td 70'feeti laeiovv{grade. 4.2 RESULTS OF SOIL ANALYSES Trace concentrations of petroleum hydrocarbons were detected in only one of the eleven samples submitted ror analyses (Table 1, Appendix C). Sample SBI-K collected at a depth of 70 feet revealed xylene concentrations of 0.013 parts per million !ppm}. Lead was not detected in sample SBI-K. The laboratory reports for the soil boring samples are enclosed in Appendix D. Results of laboratory analyses of soil samples recorded during the previous and current investigations indicate that, except for the trace levels of xylene detected in SB1-K, no BTEX components have been detected in any of the soil samples collected from the soil borings drilled at the site. • L`" I GROUNDWATER ---ter--7;— aaesMwi.apT � � TECHNOLOGY,INC.