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4 <br /> 2905 W Benjamin Holt Drive, Stockton, California March 24, 1994 <br /> Chevron USA Products Company page 6 <br /> 4.0 RESULTS OF ADDITIONAL ASSESSMENT <br /> i <br /> 41 Hydrogeology <br /> The site is located in the northern part of the San Joaquin Valley, California The valley fill consists of <br /> late Mesozoic through Eocene dominantly marine deposits overlain by late Tertiary and Quaternary <br /> non-marine deposits In the Stockton area, the late Cenozoic deposits are approximately 3,000 feet thick <br /> and generally consist of alluvial gravel, sand, silt, and clay The non-marine sedimentary units are <br /> generally fresh-water-bearing in the area of the valley east and southeast of Stockton, but brackish or <br /> saline water occurs in these sediments in the delta area west of Stockton The saline-water/fresh-water <br /> boundary within these sedimentary units trends north to south across the western portion of Stockton <br /> The saline groundwater west of this boundary Is usually overlain by a layer of fresh groundwater to a <br /> depth of approximately 50 feet BGS, therefore, shallow monitoring wells usually encounter fresh <br /> groundwater on both sides of the boundary <br /> The site is underlain by interbedded clays, silts, and silty fine sands from the surface to 6 feet BGS, and <br /> fine to coarse sand from 6 to 30 feet BGS During drilling MW-8, groundwater was encountered at 17 <br /> feet BGS During quarterly monitoring (January 18, 1994), depth to water was at approximately 16 to 18 <br /> feet BGS Groundwater flow as mapped from data collected on January 18, 1994 is to the east at a <br /> hydraulic gradient of 0 006 to 0 0002 (Figure 3) <br /> 42 Results of Soil Sample Analyses <br /> Results of the soil sample analyses are summarized in Table 1 No TPH-G or BTEX compounds were <br /> detected in the analyzed sample collected from the boring for MW-8 Copies of laboratory results and <br /> chain-of-custody manifests are included in Appendix E <br /> 43 Results of Groundwater Analyses <br /> Analytical results of groundwater samples collected from the eight wells are summarized in Table 2 <br /> Dissolved TPH-G concentrations ranged from 24,000 ppb in MW-1 to non-detectable in MW-3, MW-4, <br /> I JF';X GROUNDWATER <br /> 3831 SUM RPT �n'� TECHNOLOGY <br />