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45 E Harding Way, Stockton, California March 14, 1994 <br /> Chevron USA Products Company Page 7 <br /> 4.0 RESULTS OF ADDITIONAL ASSESSMENT <br /> 41 Hydrogeology <br /> The site is located in the northern part of the San Joaquin Valley at an elevation of approximately 12 feet <br /> above sea level The valley fill consists of late Mesozoic through Eocene marine deposits overlain by <br /> late Tertiary and Quaternary non-marine deposits which usually contain fresh water In the Stockton <br /> area, late Cenozoic deposits are approximately 3,600 feet thick and generally consist of alluvial gravel, <br /> sand, silt, and clay Groundwater in these alluvial deposits is unconfined to semiconfined <br /> The materials logged to a depth of 65 feet during drilling at the site are interbedded clayey silts and silty <br /> clays with lenses of sand Groundwater was encountered during drilling at a depth of approximately 50 <br /> feet in MW-2R and MW-14 <br /> I <br /> 42 Results of Soil Sample Analyses <br /> Results of all sod sample analyses are summarized in Table 1 No benzene was detected in any of the <br /> analyzed sod samples TPH-G was detected in sod samples collected from SB-2 and SS-3 The highest <br /> concentrations of TPH-G were detected in samples collected at 25-35 feet below grade in SB-2 and <br /> SB-3 Copies of the laboratory analyses reports and chain-of-custody manifests are included in <br /> Appendix E <br /> 43 Results of Groundwater Monitoring <br /> Groundwater monitoring was conducted January 26, 1994 The monitoring data were combined with the <br /> survey data to determine the groundwater elevation in each monitoring well (Table 2) During quarterly <br /> monitoring, average depth to water was 49 feet below grade The groundwater flow on January 26, <br /> 1994, was to the east-northeast at a hydraulic gradient of 0 007 (Figure 3) <br /> GROUNDWATER <br /> 48955UM RPT TECHNOLOGY <br />