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i <br /> I26485 THORNTON ROAD <br /> WKA No 2556 02 <br /> August 18, 1994 <br /> Page 2 <br /> Ideposited during the filling of a large ancient basin. The 1985 United States Geological Survey <br /> (USGS) "Geologic Map of the Late Cenozoic Deposits of the Sacramento Valley and Northern <br /> Sierra Foothills, California," shows the site to be underlain by Holocene age basm deposits <br /> These deposits consist primarily of fine-grained silt and clay <br /> IThe site lies within the Sacramento/San Joaquin River Delta. The upper ground water table is <br /> unconfined and approximately 11 feet below grade Based on our experience m the area and the <br /> I1990 and 1992 Ground Water Elevation Contour Maps published by the Sacramento County <br /> Department of Public Works, Water Resources Division and the San Joaquin County Flood <br /> iControl and Water Conservation District, the regional ground water flow direction is primarily <br /> toward the northeast. <br /> SITE HISTORY <br /> Two 1,000-gallon gasoline USTs were removed from the site by Aronson Engineering on June 2, <br /> I1993 Analysis of samples obtained from beneath the easterly ends of the USTs revealed Total <br /> Petroleum Hydrocarbons (TPH) as gasoline concentrations ranging from 100 mg/kg to 510 <br /> mg/kg Analysis of samples obtained beneath the former dispenser revealed no detectable <br /> concentrations of TPH gasoline and only trace concentrations of xylene. Additionally, analytical <br />' results for the sample SW1 obtained from the sidewall of the excavation revealed a TPH gasoline <br /> concentration of 4 1 mg/kg <br />' Analytical results for samples W1 and W2, obtained from the water in the excavation, revealed <br />' TPH gasoline concentrations ranging from 240 µg/f to 2,300 µg11 <br /> A more detailed discussion of the laboratory results and observations during tank removal is <br />' contained in our Soils Sampkng and Testing report, dated June 23, 1993, on file with San <br /> Joaquin County Environmental Health Division (EHD) <br /> 1 <br />' WALLACE•KUHL <br /> Recycled paper &ASSOCIATES INC <br />