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40 feet below grade from BH-I revealed no detectable diesel fuel concentrations, however, <br /> minor volatile petroleum hydrocarbon concentrations were noted <br /> Analysis of soil samples collected in January 1991, during the installation of vapor extraction <br /> wells MW-6, MW-7, MW-8, and MW-9 revealed detectable diesel fuel concentrations in <br /> samples from MW-6 and MW-7 only No detectable diesel concentrations were encountered <br /> in the MW-8 and MW-9 soil samples No detectable volatile petroleum hydrocarbon <br /> concentrations were detected in any of the soil samples collected from the extraction wells <br /> Vapor well MW-6 was installed directly through the former tank location (adjacent to former <br /> borehole BH-1) Vapor wells MW-7, MW-8, and MW-9 were installed to the north, <br /> southeast, and west of MW-6, respectively within a maximum distance of 16 feet from the <br /> former tank location <br /> Analytical results appear to confirm previous findings that impacted soils are generally <br /> concentrated within ten feet of the former tank location with the greatest concentrations of <br /> fugitive petroleum hydrocarbons located directly beneath the former tank location <br /> Comparison of the November 1988 with the January 1991 results, appear to indicate a general <br /> decrease in petroleum concentrations from the original samples to the subsequent sample in <br /> adjacent locations <br /> In 1988, the maximum diesel concentration encountered was 7,100 ppm at a depth of 30 feet <br /> below grade (BH-1), whereas in 1991 the maximum diesel concentration encountered was <br /> 4,900 ppm at 25 feet below grade (MW-6) In addition, the 1991 soil sample collected at 35 <br /> feet below grade revealed no detectable petroleum hydrocarbons (MW-6) A decrease in <br />' diesel concentrations was also noted north of the tank excavation from 150 ppm at 15 feet <br /> below grade in 1988 (BH-5) to 89 ppm at 15 feet below grade in 1991 (MW-7), and west of <br /> the tank excavation from 110 ppm at 15 feet below grade in 1988 (BH-4) to below detection <br /> limits in all samples in 1991 (MW-9). No detectable volatile hydrocarbons were detected in <br /> January 1991 in comparison to detectable concentration encountered in all but one sample in <br />' 1988 <br /> Analysis of soil samples collected from boreholes SB-I and SB-2 in October 1993, revealed a <br /> detectable diesel concentration (2,900 ppm) in only one sample collected at 15 feet below <br /> grade from SB-1 No detectable volatile petroleum hydrocarbon concentrations were <br /> M7,J01-27-95/UST/95-0011 nbr 8 <br />