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45 East Haraing Way, Stockton, California July 22, 1992 <br /> Chevron U S A Products Company Page 7 <br /> 4 0 SITE CONDITIONS <br /> 41 Hydrogeology <br /> The site is located in the northern part of the San Joaquin Valley at an elevation of <br /> approximately 12 feet The valley fill consists of late Mesozoic through Eocene dominantly <br /> marine deposits overlain by late Tertiary and Quaternary dominantly non-marine deposits which <br /> usually contain fresh water In Stockton area, the late Cenozoic deposits are approximately <br /> 3,000 feet thick and generally consist of alluvial gravel, sand, silt, and clay Groundwater in <br /> these alluvial deposits is usually unconfined to semiconfined Extensive Plio-Pleistocene <br /> lacustrine deposits, including the diatomaceous Corcoran Clay, occur in San Joaquin Valley, <br /> south of Stockton The water beneath the clay bed is usually confined <br /> The materials penetrated to a depth of 75 feet during drilling at the site are dominantly clays <br /> with lenses of sand and silt The water table, which was at a depth of about 40 feet in Fall of <br /> 1989, has been declining and most of the site-related monitoring wells are currently dry <br /> On May 1, 1992, only three wells, MW-9 and the two new wells, MW-10 and MW-11, <br /> contained groundwater, the water table was measured at approximately 53 feet below grade <br /> Estimated groundwater flow is to the northeast at a gradient of approximately 0 004 <br /> 42 Results of Soil Analyses <br /> Results of all soil samples analyses are summarized in Table 1 and the laboratory reports are <br /> enclosed in Appendix D Benzene (0 12 ppm) and TPH-G (730 ppm) were detected only in the <br /> soil sample collected at a depth of 30 feet in V-6 (designated as VW-6 in Table 1 and the <br /> laboratory reports) <br /> 43 Results of Groundwater Analyses <br /> Results of all water sample analyses are summarized in Table 2, and the laboratory reports are <br /> enclosed in Appendix D Ali three sampled monitoring wells contained dissolved hydrocarbons <br /> with the highest concentrations detected in MW-11 (2,800 ppb TPH-G and 1,500 ppb <br /> benzene) <br /> 111-101 l� GROUNDWATER <br /> L_.,1 i_� TECHNOLOGY <br />