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. GEOLOGY <br /> The site is located in the San Joaquin Valley of the Central Valley geomorphic province Recently <br /> published geologic maps indicate that Holocene age flood-basin deposits extend from ground <br /> surface to a maximum depth of approximately 100 feet below the site Oligocene to Holocene <br /> age alluvial deposits lie below the younger flood-basin deposits to a maximum depth of <br /> approximately 3,500 feet below ground surface Continental and marine rocks of pre-Tertiary to <br /> Oligocene age underlie the alluvial deposits, and are composed of shale, sandstone and <br /> conglomerate Crystalline bedrock underlies the sedimentary formations <br /> Based on the drilling logs, sediments beneath the site consists mostly of silty clay and clayey silt <br /> from the surface to approximately 65 to 70 feet bgs At this depth a sand layer occurs which is <br /> approximately 5 to 10 feet thick and contains various fractions of silt and clay Underlying the <br /> sand layer at approximately 75 feet, the section is characterized by the silty clay/clayey silt <br /> sediments typical of the upper section, to at least 90 feet bgs Figures 3A and 3B are geologic <br /> • cross sections which shows the generalized lithologic relationships The drilling logs from this <br /> investigation contain descriptions of the sediments encountered and are presented in Appendix A <br /> HYDROGEOLOGY <br /> At the time of WCC's investigation in 1988, groundwater was encountered beneath the site at <br /> approximately 50 feet bgs within the silty clay sediments Well MW3 was installed to 50 feet bgs <br /> and wells MW1 and MW2 were installed to approximately 60 feet bgs Because only two wells <br /> contained significant groundwater quantities, the hydraulic gradient could not be measured at that <br /> time <br /> During drilling in November 1992, groundwater was encountered at 80 feet bgs, indicating a <br /> significant drop in the local water table had occurred Because of this decrease in groundwater <br /> elevation, none of the shallow monitoring wells contained groundwater and only wells MW3R, <br /> Page 3 <br />