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5431 Grant Line Road, Banta, California April 7, 1994 <br /> Chevron USA Products Company Page 6 <br /> 4.0 RESULTS OF ADDITIONAL ASSESSMENT <br /> 41 Hydrogeology <br /> The site is located in the northwestern part of the San Joaquin Valley at an elevation of approximately 22 <br /> feet The valley fill consists of late Mesozoic through Eocene dominantly marine deposits overlain by <br /> late Tertiary and Quaternary dominantly non-marine sediments which usually contain fresh water The <br /> late Cenozoic deposits generally consist of alluvial gravel, sand, silt, and clay Groundwater in these <br /> alluvial deposits is unconfined to semiconfined Plio-Pletstocene lacustrine deposits, including the arealy <br /> extensive diatomaceous Corcoran Clay, occur in San Joaquin Valley southeast of Banta The water <br /> beneath the clay bed is usually confined <br /> The materials penetrated to a depth of 15 feet during drilling at the site are dominantly clayey silts and <br /> silty clays with lenses of sand Groundwater was encountered during drilling at a depth of approximately <br /> 13 feet in the wells monitored The data collected during the January 6, 1994 monitoring event were <br /> used to prepare a potentiometric surface map that depicts a northwest groundwater flow direction at a <br /> gradient of approximately 0 002 (Figure 3) <br /> 42 Results of Soil Sample Analyses <br /> Table 1 summarizes the laboratory analytical results of soil samples collected January 5, 1994 Only one <br /> soil sample, collected from S84 at 10 feet below grade, contained 0 007 ppm benzene and 0 005 ppm <br /> ethylbenzene TPH-G and TPH-D were not detected in any of the analyzed soil samples Copies of <br /> laboratory analyses reports and chain-of-custody manifests for the soil samples collected January 5, <br /> 1994 are included in Appendix E <br /> 43 Results of Groundwater Analyses <br /> Groundwater analytical results for samples collected from wells MW-1 and TW-1 were below method <br /> detection limits (<MDL) for BTEX, TPH-G, and TPH-D The groundwater sample collected from TW-2 <br /> was <MDL for BTEX and TPH-D, but contained 55 ppb TPH-G The rinsate blank collected after <br /> sampling TW-2 was reported to contain 61 ppb TPH-G Copies of laboratory analyses reports and <br /> chain-of-custody manifests for groundwater samples collected on January 6, 1994 are included in <br /> Appendix E <br /> 71 <br /> ice_ L GROUNDWATER <br /> 4a94EAR Rpr �' _ 7�1 TECHNOIACY <br />