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was analyzed for total petroleum hydrocarbons as diesel (TPHd)by EPA Method 3510/8015 and <br /> the fuel components benzene, toluene, ethylbenzene,and xylenes(BTEX)by EPA Method 8020. <br /> The results of the laboratory analyses indicate that TPHd and BTEX compounds were not <br /> present in the soil sample at concentrations above the detection limits. Laboratory data sheets <br /> and the accompanying chain-of-custody record are attached. <br /> Source of Residual Diesel Fuel in Backfill Materials <br /> The results of RFS' additional pipeline trench sampling and initial subsurface soil investigation <br /> indicate that the native soils surrounding and beneath the abandoned 6000-gallon UST pit and <br /> pipeline trench have not been affected by petroleum hydrocarbons. Residual petroleum <br /> hydrocarbons, however, were detected in samples obtained from the gravel backfill materials <br /> excavated during UST removal activities. The two samples obtained from the backfill material <br /> overlying the UST contained concentrations of 17 and 230 ppm TPHd, 0.016 ppm ethylbenzene, <br /> and 0.047 ppm xylenes. <br /> The source of the residual diesel fuel in the backfill materials overlying the UST is not known. <br /> However, based upon the operation of a continuous tank monitoring system since 1989 (without <br /> incident), UST tightness testing results, and the condition of the tank at the time of removal, the <br /> presence of detectable concentrations of TPHd in the backfill materials overlying the UST is <br /> likely to have been a result of overspill during tank filling or possibly a minor pipeline release <br /> during the tank removal or the 1989 system upgrade activities. The integrity of the UST and <br /> the absence of detectable concentrations of TPHd or BTEX in the native soils surrounding and <br /> beneath the abandoned UST pit indicate that the residual hydrocarbons in the backfill material <br /> were not a result of a failure of the UST or the associated pipelines. <br /> Based upon the results of the additional pipeline trench sampling and initial subsurface soil <br /> investigation, RES concludes that no further investigation or remediation of the UST site is <br /> necessary. <br /> Sincerely, <br /> RIEDEL ENVIRONMENTAL SERVICES, INC. <br /> Christopher$. White, RG 4983 <br /> Senior Geologist <br /> Attachments <br /> cc: Diane Hinson <br /> San Joaquin County <br /> Public Health Services <br /> Environmental Health Division <br /> 4185\CBW4\SPRLYr.ADD\1 SOCT94 2 <br />