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grade (110 ppm and 2,800 ppm) which decreased to non-detectable levels between 23 and <br /> 27 5 feet below grade <br /> A final round of verification sampling was conducted on November 18, 1993 Analysis of <br /> these soil samples revealed the presence of diesel fuel to a depth of 26 feet below grade <br /> which extends laterally up to five feet north of the former middle tanks west end <br /> Recent drilling efforts were positioned so as to examine current soraY <br /> ualit in the area <br /> q <br /> previously observed to contain detectable petroleum hydrocarbons (near the west end of the <br /> former middle UST) The new bonngs VW-A and VW-B were drilled in positions adjacent <br /> to the locations where the greatest diesel concentrations were previously encountered Soil <br /> samples were collected every 2 5 feet through the diesel impacted zone (15 to 30 feet below <br /> grade) Analysis of these samples revealed no detectable BTEX concentrations No <br /> detectable diesel concentrations were encountered in the samples collected from borehole <br /> VW-A Diesel was encountered in the samples collected from borehole VW-B at 22 5 and <br /> 25 0 feet below grade only (I 10 ppm and 2 1 ppm, respectively) <br /> One sample from each borehole was analyzed to determine the soluble threshold limit <br /> concentration of diesel Analysis of these samples revealed no detectable leachable (mobile) <br /> concentrations of diesel One sample from borehole VW-A was additionally analyzed for <br /> total organic matter Analysis revealed the sample contained 0.19 % organic material A <br /> summary of recent sidewalk soil sample analytical results is depicted on Figure 7 and listed in <br /> Table 2 <br /> 6.3 Residual Diesel Fuel Calculations <br /> 6.3.1 Basement Area <br /> Review of soil sample analytical results to date for this area indicate diesel fuel <br /> concentrations have been relatively constant over the period observed The average residual <br /> diesel fuel concentration of 12,036 ppm is an average of 10 measurements from the <br /> appropriate depth range and impact area The following calculations provide an order of <br /> magnitude volume estimate of the remaining residual diesel <br /> Area - Point six feet deep immediately beneath the former } <br /> gallon) tank location and <br /> { g <br /> extending outward in a six-foot square on both sides <br /> MZ/0406-95/UST/95-0089 7 <br />