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from soil borings placed in areas expected to contain the highest concentrations of residual TPH, based on all previous data and field observations Soil samples were also collected from MW-5 which was installed beneath the 500-gallon former waste oil tank Soil samples from borings B-19 and B-20 were collected and analyzed for TPH-d at five-foot intervals from approximately 20 feet bgs (the nominal base of the excavation) to 40 feet bgs Soil samples were collected at 10-foot intervals from DMW-5 Previous results (summarized in Dames & Moore, 1992, 1994a) suggest residual TPH-d less than 10,000 mg/kg would be encountered in these areas at approximately 20 to 30 feet bgs To evaluate hydrocarbon mobility in soils, the samples with the highest concentration of TPH-d were analyzed for total and WET (dezomzed water) extractable semivolatnle hydrocarbons known to be present in diesel The purpose of testing both total and WET extractable TPH constituents is to estimate the leachable fraction of TPH-d, and the most mobile diesel component naphthalene In addition to the analysis for hydrocarbon mobility in soils, PHS-EHD requested BTXE and volatile halogenated hydrocarbon analysis in selected soil samples PHS-EHD also requested an additional round of groundwater sampling and analysis for TPH-d, TPH-g, and BTXE in new and existing wells, and volatile halogenated organics in the new well, DMW-5 4 0 RESULTS AND DISCUSSION This Section presents a discussion of the results from the soil and groundwater analyses, evaluates the mobility of residual hydrocarbons in soils and assesses any related impact on groundwater at the Site A general discussion of the hydrocarbon concentrations in soils with depth below ground surface (bgs) is followed by the results from total and WET extractable semivolatile constituents of diesel (including naphthalene) The results of the 1995 groundwater sampling and analysis activities are presented, and includes a brief discussion of groundwater chemistry and water level information The potential for TPH-d and diesel constituents to impact groundwater at the Site was evaluated by employing a guidance document Designated Level Methodology (DLM) (RWQCB, 1989) prepared by the RWQCB and accepted by PHS-EHD 4 1 DISTRIBUTION OF TPH IN SOILS . Table 1 presents the results of TPH-d, TPH-g, and BTXE analyses conducted on the soil samples collected from the two soil borings (SB-19 and SB-20), and the momtorung well (DMW-5) SAC156 14 DAMES &MOORE