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• concentration in this sample was 1,800 ppm TPPH and BTEX concentrations were below or near <br /> detection limits in the soil samples collected from the former UST excavation <br /> Additional investigation performed during October 1997 included drilling two soil borings with <br /> Geoprobe equipment to determine the vertical extent of petroleum hydrocarbons and MTBE <br /> previously identified during tank removal activities Soil boring SB-1 delineated the vertical extent <br /> of the petroleum hydrocarbons and MTBE in the northwest corner of the former tank complex Soil <br /> boring SB-2 was drilled to the depth of 35 5 fbg where drilling refusal was encountered The final soil <br /> sample collected at 35 5 fbg contained TPPH at a concentration of 5,700 ppm and ND levels of <br /> benzene and MTBE <br /> Based on ground water monitoring data from a nearby site, depth to ground water at this site is <br /> believed to be 55 to 65 fbg and ground water flow direction is believed to be southerly <br /> TECHNICAL RATIONALE FOR PROPOSED SCOPE OF WORK <br /> Soil sampling data from the previous investigation indicate that petroleum hydrocarbons are <br /> present in the soils at depths to 35 5 fbg beneath the northern-most product island near <br /> Fremont Street Vertical delineation of petroleum hydrocarbons in this area is incomplete <br /> • • There is no evidence that ground water has been impacted by petroleum hydrocarbons or <br /> MTBE at this site <br /> Additional vertical delineation of petroleum hydrocarbons in soil beneath the northern-most <br /> product island is proposed by drilling a soil boring with hollow stem auger drilling equipment <br /> This boring will be drilled to the depth where ground water occurs and a ground water sample <br /> will be collected and analyzed <br /> • If petroleum hydrocarbons or oxygenate compounds are present in the ground water sample <br /> collected from the boring, the boring will be converted to a ground water monitoring well and <br /> two additional wells will be drilled and installed on-site However, if petroleum hydrocarbons <br /> and oxygenate compounds are not present in the ground water sample collected from the <br /> boring and soil samples from the boring indicate that petroleum hydrocarbons and oxygenate <br /> compounds have not migrated to the depth of ground water, no monitoring wells will be <br /> installed <br /> WORK TASKS <br /> Permits An appropriate permit for drilling will be obtained from SJCPHS <br /> Health and Safety Plan A site-specific Health and Safety Plan will be prepared for field work <br /> 240-0797 2 <br />