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Elevated concentrations of total petroleum hydrocarbons in soil at the site were first noted in May of 1988, when seven underground storage tanks were removed from the ground. During excavation of the tanks, evidence of leakage from the tanks, including soil staining by hydrocarbons, was reportedly observed. Although the total volume of hydrocarbons released from the seven tanks is not known by Dames & Moore, soil staining had been observed to a depth of 16 feet below the ground surface. Analyses completed on nine soil samples obtained during UST removal -• confirmed that the soils beneath several of the excavated tanks contained hydrocarbon constituents. w To determine the extent of hydrocarbon constituents observed in the soil during the tank excavations, an initial site s investigation was performed. This investigation included the installation of four monitoring wells onsite; MW-1 at the formar location of six of the underground storage tanks, MW-»2 at the former location of the seventh underground tank (the waste oil tank) , MW-3 and MW-4 to the north of the UST locations. The water table was found at 22 feet to 27 feet below the ground surface during this investigation. Soil, samples were collected during drilling for well installation at five foot intervals and selected sample_ were analyzed for hydrocarbons. Ground water samples collected from the four monitoring wells were analyzed for hydrocarbons and chlorinated solvents. The results from the soil and water analyses showed that only soil samples from MW-1 contained elevated levels of hydrocarbons. Ground water samples from both MW-'i and MW-2, however, showed elevated concentrations of hydrocartors, water samples from MW-1 also showed elevated levels of chlorinated solvents. No F chlorinated solvents were detected in water samples from MW-2, MW- 3, or MW-4. Results from the soil gas survey conducted at the, Holt Brothers Tractor company facility indicated evideince of benzene, toluene, and xylene (BTX compounds) in the soil vapors beneath the facility. The highest;cor,^entrations of BTX compounds were in the vicinity of the tank excavation backfill, adjacent to the loading ramp. The soil gas concentrations appeared to migrate out radially away from the excavation. The data suggested that constituent concentrations decreased with distance from the backfill and tended to migrate slightly in what appeared to be a westerly direction. The plume delineated by the soil gas survey encompassed the six UST excavations and extended to the east under the paint shop, and approximately" 100 feet west of the loading ramp. The concentration contour plots, however, do not directly correlate to ground water cc;isrituent concentrations and plume location, and subsurface conditions such as soil matrix, heterogeneity, and soil moisture affect the transport and distribution of vapors. LD01.064 2