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r <br /> 3.4 Groundwater Quality Data <br /> No groundwater samples were collected during this investigation, however results of a recent <br /> quarterly well sampling event (July 1994) conducted at the site revealed no detectable <br /> concentrations of petroleum hydrocarbons <br /> 4.0 Conclusions <br /> Review of boring logs and recent geotechnical soil testing results indicates that the former <br /> tank location has been backfilled with sand, gravel, and silt fill material, and is underlain <br /> generally by coarse grained matenals with varying concentrations of fines A silt/clay layer <br /> has been noted between 25 and 32 feet below grade <br /> rAnalysis of verification soil samples collected in November 1993 following tank removal <br /> indicated the presence of detectable diesel fuel between 17.5 and 27 5 feet below grade <br /> Based on review of these analytical results, it appears that diesel impacted soils are limited in <br /> extent to an area measuring approximately 21' wide x 10' long by 10 feet deep <br /> (approximately 78 yd3) The location of the diesel impacted soils is the area adjacent to the <br /> east end of the new tank (or the west end of the former middle tank), beginning at 17 5 feet <br /> below grade <br /> Analysis of recent soil samples (collected in July 1994 from the east end of the new tank) <br /> appear to indicate that diesel levels in soil have decreased significantly with time Only <br /> residual diesel concentrations were encountered in the samples collected at 22 5 and 25 0 feet <br /> below grade in borehole VW-B <br /> Soil samples were tested for the presence of volatile petroleum hydrocarbons with no <br /> detectable concentrations encountered The lack of volatile petroleum hydrocarbon <br /> concentrations also appears to indicate that the diesel present in the site soil may be naturally <br /> degrading with time. <br /> rOne soil sample from each borehole was using analyzed the soluble threshold limit <br /> Y g <br /> concentrations (STLC) procedures This test method involves determining the concentration <br /> of waste that will leach from a soil sample and potentially migrate to groundwater Results <br /> of the STLC testing indicated no detectable petroleum hydrocarbon concentrations which are <br /> potentially "mobile" <br /> Mv09-08-94/UST/94-0142 nbr 9 <br />