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r <br /> a <br /> r Ll CPIVE <br /> L <br /> EXECUTIVE SUMMARY AUG '92 <br /> PRELIMINARY SITE INVESTIGATION REPORTENVIRQNMENTAL HEALTH <br /> PERMIT/SERVICES <br /> for <br /> California Department of Transportation v <br /> Stockton Maintenance Facility <br /> 1604 South B Street <br /> Stockton, California <br /> July 9, 1992 <br /> This report presents results and findings of the preliminary site <br /> investigation performed at Caltrans Stockton Maintenance <br /> Facility, 1604 South B Street, Stockton, California. The <br /> investigation was performed in accordance with requirements and <br /> 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 <br /> activities necessary to: (1) determine the nature and extent of <br /> hydrocarbon-affected soil and ground water; and (2) develop an <br /> appropriate course of action for additional investigation in <br /> accordance with the requirements of the regulatory agencies. <br /> a <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 /> o Review of subsurface geology indicates the site is <br /> underlain by predominately silty sand and poorly-graded <br /> sand with interbedded silty clay and sandy clay units. <br /> ® Concentrations of total petroleum hydrocarbons as <br /> gasoline (TPH-G) of 30 parts per million (ppm) to 120 <br /> ppm were detected in soil samples collected in the <br /> southern limit of the former diesel tank cavity at an <br /> approximate depth of 46 feet below grade (fbg) . <br /> ® Total petroleum hydrocarbons as diesel (TPH-D) was not <br /> detected at or above the reported detection limit in <br /> soil samples analyzed with the exception of samples <br /> from MW-3 at 31 ppm and SB-1 at 3 .8 ppm at 46 fbg, <br /> however, laboratory reports indicate that these samples <br /> appeared to contain kerosene, not diesel (see notes at <br /> the bottom of official laboratory reports, Appendix G) . <br /> • Benzene was detected in soil samples collected from <br /> each boring at depths ranging from 35 fbg to the <br /> capillary fringe (66 fbg) . The highest concentrations <br />