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PROPOSED SCOPE OF WORK <br /> FOR <br /> iUPPLEMENTAL SITE INVESTIGATION <br /> AND <br /> REMEDIAL PLANNING STUDY <br /> California Department of Transportation <br /> Shop 10 Facility <br /> 1603 South B Street <br /> Stockton, California <br /> INTRODUCTION <br /> This work plan presents the proposed scope of work to conduct <br /> a supplemental site investigation and remedial planning study <br /> at California Department of Transportation (Caltrans) Shop 10 <br /> facility, 1603 South B Street, Stockton, California. The <br /> proposed scope of work is based on the previous underground <br /> storage tank removal activities and investigations at the <br /> site. A site vicinity is included as Figure 1. <br /> BACKGROUND <br /> In 1987 , four ground water monitoring wells (MW-1, MW-2 , <br />. MW-3 , and MW-4) were installed to an approximate depth of <br /> 50 feet below grade (fbg) in the immediate vicinity of four <br /> 5000-gallon underground storage tanks by Woodward-Clyde <br /> Consultants (WCC) . WCC also performed ground water monitoring <br /> and sampling of these wells. -Ground water was encountered at <br /> 40 fbg. Analysis of the ground water samples detected total <br /> petroleum hydrobons as gasoline (TPH-G) ranging from 154 , 000 <br /> parts per billion (ppb) in MW-2 to 231, 000 ppb in MW-3 . These <br /> concentrations are indicative of emulsified free product. <br /> WCC subcontracted Pacific (NET) to perform a soil gas survey <br /> of the underground storage tank area. In June 1988 , NET <br /> collected 26 soil gas samples and analyzed for TPH-G, and <br /> benzene, toluene, and xylenes (BTX) . Concentrations of TPH-G <br /> and/or BTX were detected in the majority of the samples <br /> collected at depths ranging from 7 to 33 fbg. The highest <br /> concentration of TPH-G (300 ppm) was detected in the area of <br /> the underground storage tanks at a sample depth of 7 fbg. <br /> In February 1989, the four underground storage tanks, and the <br /> waste oil tank were removed by Placer Tractor Services. Eight <br /> soil samples were taken from the tank removal excavation and <br /> analyzed for total petroleum hydrocarbons as diesel (TPH-D) , <br /> TPH-G, BTX and ethylbenzene (BTEX) , organic lead, and ethylene <br /> dibromide. TPH-G was detected in the soil samples taken from <br /> the tank cavity with concentrations ranging from 0. 023 ppm in <br /> the west wall at 14. 5 fbg to 3 . 7 ppm in the southeast corner <br /> at approximately 14 fbg. TPH-D was detected in two samples <br />