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09 September 1996 <br /> AGE-NC Project No 95-0173 <br /> IPage 2 of 8 <br /> Iare summarized in Table l -Analytical Results Of UST Removal <br /> 23 REGIONAL GEOLOGIC SETTING <br /> The subject site is located in the eastern portion of the Great Valley geomorphic province of <br /> California The valley is a nearly flat, elongate trough trending northwest and southeast for <br /> approximately 450 miles The valley is enclosed by the granitic Sierra Nevada on the east and the <br /> sedimentary and metamorphic Coast Ranges on the west The surficial and upper several hundred feet <br /> of subsurface layers consist primarily of unconsolidated alluvial and floodplain deposits <br /> (predominantly sand, silt, and clay) of Quaternary age, which were derived from the mountains of the <br /> Sierra Nevada Beneath the upper sedimentary deposits lie a thick sequence of marine deposits of <br /> lMesozoic age, which in turn are underlain by a pre-Jurassic complex of igneous and metamorphic <br /> basement rock <br /> I <br /> 2 4 GROUND WATER DEPTH AND GRADIENT <br /> The water-table surface beneath the site occurs at a depth of approximately 35 feet below surface <br /> grade (bsg) The uppermost ground water flows in an unconfined aquifer With increasing depth, the <br />' aquifer becomes semi-confined, due to the presence of mixed heterogeneous layers of sediments <br /> Ground water contour maps published by the San Joaquin County Flood Control and Water <br />' Conservation District indicate that regional ground water flow is towards the northeast <br />' 3.0. PROCEDURES <br /> 3 1 SCOPE OF WORK <br />' The scope of work was to perform a preliminary site characterization of the hydrocarbon impact <br /> related to the former USTs To meet the objective a subsurface investigation, which included drilling <br /> of six soil borings, unstallation of four two-inch ground water monitoring wells, followed by collection <br /> and analysis of both ground water and soil samples, was conducted <br /> I <br /> 32 DRILLING <br /> On 25 and 26 July 1996, six soil borings (B-1, B-2, and MW-1 through MW-4) were advanced at the <br /> site utilizing a CME-75 truck mounted drill rig equipped with eight-inch diameter hollow stem augers <br />' Soil borings MW-1 through MW-4 were advanced to a depth of 50 feet bsg, B-1 was advanced to <br />