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1IS • petroleum hydrocarbon concentration in the influent stream reached an asymptotic condition The SVE system utilized SVE wells that were screened from 14 to 44 feet bgs Figures 4, 5, and 6 depict soil conditions beneath the site prior to operation of the SVE system (November 1990 -November 1992) Cu,-rent site conditions are discussed below Currently, residual hydrocarbons in soils occur below the northeast corner of the former UST cluster (installed in 1984) and adjacent product island These hydrocarbon affected soils occur in what can be described as two localized vertical soil columns Hydrocarbon affected soils in these two vertical soil columns occur from a depth of approximately 15 feet to 50 feet, bgs The horizontal extent of hydrocarbon affected soils within these soil columns occur primarily within a range of 5 to 10 feet, with occasional thin zones that extend horizontally an additional 10 feet from the soil column These soil columns occur within vadose zone soils, soils within the capillary fringe and zone of groundwater fluctuation, and currently saturated soils Figures 7, 8, and 9 depict these conditions and show soil analytical data from soil borings and wells drilled after the operation of the SVE system A further discussion of the occurrence of these hydrocarbons are discussed below The location of the residual hydrocarbons in soils are characterized by soil borings located in two areas These include soil Borings SB-2 and SB-12 located in the northern portion of the UST complex and Borings SB-3 and SB-13 located adjacent to the western product island • Hydrocarbons in these two areas are well defined and appear to be isolated based on data collected from several borings as shown on the geologic cross-sections(Figures 8 and 9) The concentration of the residual hydrocarbons in soils are characterized by the presence of the relatively high molecular weight compounds as discussed above TPH g concentrations range in concentration from less than 10 ppm to 10,000 ppm Benzene with few exceptions has not been detected Residual hydrocarbons as dissolved hydrocarbons are primarily affected by (1)hydrocarbon- affected vadose-zone soils typical of source areas, (2)residual hydrocarbons left in soil by groundwater fluctuation, (3) operation of the SVE system, and (4) intrinsic remediation (mechanisms including biodegradation, chemical oxidation, and adsorption/absorption) Dissolved hydrocarbon concentrations in groundwater samples collected from Well MW-9, located in the source area, have generally decreased with the overall increase in groundwater elevation This trend indicates that SVE was effective in remediating hydrocarbon-affected soils in the source area Dissolved hydrocarbons were not detected in groundwater samples collected from Well MW-9 during the second quarter 1995 Groundwater samples collected from Well MW-13, during the second quarter 1995, contained TPH-g and benzene at concentrations of 1,500 and 6 5 parts per billion (ppb), respectively The hydrocarbon concentration in groundwater samples collected from this well may be the 3201337B/1918REV 4 August 31, 1995