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1 , <br /> clu A �V <br /> EXECUTIVE SUMMARY AUG 9 2 <br /> SUPPLEMENTAL SITE INVESTIGATION ENVIRONMENTAL HEALTHPERMIT/SERVICES <br /> for <br /> California Department of Transportation <br /> Shop 10 Facility <br /> 1603 South B Street <br /> Stockton, California <br /> July 13, 1992 <br /> This report presents results and findings of the supplemental <br /> site investigation performed at Caltrans Shop 10 Facility, <br /> 1603 South B Street, Stockton, California. The supplemental site <br /> investigation was performed in accordance with the requirements <br /> and guidelines of the San Joaquin County Public Health Department <br /> (SJCPHD) and the California Regional Water Quality Control Board, <br /> Central Valley Region (RWQCB) . The scope of work included tasks <br /> and activities necessary to: (1) assess the nature and extent of <br /> hydrocarbon-affected soil and ground water; and (2) develop an <br /> appropriate course of action for additional investigation. <br /> FINDINGS AND CONCLUSIONS <br /> The findings and conclusions based on the results of subsurface <br /> investigative work performed at the site are summarized below: <br /> 0 Review of subsurface geology indicates the site is <br /> underlain by predominately silty sand and poorly-graded <br /> sand with interbedded silty sand and silty clay kinits. <br /> Q Concentrations of 270 and 4 parts per million (ppm) of <br /> total petroleum hydrocarbons as gasoline (TPH-G) were <br /> detected in soil samples collected beneath the former <br /> tank cavity at depths of 46 and 56 feet below grade <br /> (fbg) . <br /> o Concentrations of 4 . 4 ppm and 0. 81 ppm of benzene were <br /> detected in soil samples collected beneath the farmer <br /> tank cavity at depths of 46 and 56 fbg. <br /> o The former underground fuel tanks and/or associated <br /> product lines are the likely source of the adsorbed- <br /> phase hydrocarbons. <br /> 0 Ground water has been impacted with dissolved-phase <br /> hydrocarbons. This may have been caused by the <br /> adsorbed-phase hydrocarbons detected in the soil. <br /> o Based on hydrogeologic conditions at the site and <br /> results of field activities and laboratory analysis <br />