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i <br /> 3.5 Soil Conditions <br /> A total of eight soil borings and the exploratory excavation were used to complete the subsurface <br /> investigation at the site. Logs of the soil borings are presented in Appendix 4. The sediments <br /> penetrated in the soil borings indicate that the main portion of the site soil petroleum hydrocarbon <br /> contamination has been contained in the near surface silt and fine grained sand that exists at a depth <br /> not greater than 16.5 feet The sediments impacted are part of the Modesto Formation(Figure 8 and <br /> 9). <br /> The vast majority of contaminated soil was contained in the soil between 6.5 and 16.5 feet bgs. Soil <br /> petroleum hydrocarbon contamination was identified during the 1999 and 2008 exploratory drilling <br /> programs at the site by: (1) visual, dark gray to black stained soil; (2) odor- strong petroleum <br /> hydrocarbon smell; (3)PID-MiniRae 2000 instrument indicated organic vapors present at least 2 to <br /> 5 times over background in instrument readings (ppmv), and; (4) laboratory analytical results from <br /> soil samples. <br /> The petroleum h drocar o' <br /> n contamination at the. site was identified as primarily as diesel <br /> contaminated soil. Based on site history this diesel fuel was introduced into the subsurface by <br /> spillage from the fueling operations. The ratio of volatile organic compounds and TPH-d <br /> concentrations all suggest this release was an older release. The leakage most likely occurred during <br /> the life span of the fuel tanks (mid-1970s to 1998). <br /> Figure 9 is a map that depicts the areal distribution of petroleum hydrocarbon constituents in the soil <br /> at the site. The distribution of the petroleum constituents at the site is greatest immediately adjacent <br /> to the fuel tank location(Figures 10 and 11). Petroleum hydrocarbon concentrations obtained from <br /> soil samples from soil borings appear to be highest immediately below or adjacent to this UST <br /> (Figures 10 and 11). Figure 9 depicts the horizontal extent of petroleum hydrocarbon soil <br /> contamination at the site. The total estimated areal extent of petroleum hydrocarbon soil impact <br /> remaining in place is estimated to be approximately 400 square feet. <br /> EnvironmentaBSTETARSCR09102008.wpd 21 <br /> I <br /> I <br /> I - <br />