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highest concentrations 'of TPHg are present in soil northwest of the former location of the <br /> gasoline USTs. Similarly, as indicated on Figure 6, the highest concentrations of benzene are <br /> `' present in soil northwest of the former location of the gasoline USTs. These patterns of aereal <br /> • extent of TPHg and benzene, and the presence of these contaminants in the capillary fringe are <br /> Lo indicative of groundwater impact and transportation. Historical soil analytical results and <br /> results from this investigation are presented on Table 1. <br /> As stated .in Section 4.1, the lithology of the capillary fringe is primarily silty clay, with <br /> I Lo clayey sand in some areas. The capillary fringe in the vicinity of wells MW 1,. MW2 and <br /> MW3 was observed to be silty clay. Petroleum hydrocarbons in groundwater would readily <br /> adsorb to the clayey soil in the capillary fringe. <br /> • 5.1.2 Saturated Zone <br /> `. Based on field observations and PID measurements, petroleum affected soil appears to <br /> attenuate rapidly with depth in the saturated zone. Soil samples were not analyzed from the <br /> LW saturated zone during this investigation, however, laboratory data from the previous <br /> investigation indicates nondetectable concentrations of petroleum hydrocarbons at 25 feet bgs. <br /> Historical soil analytical results and results from this investigation are presented on Table 1. <br /> ` <br /> 5.2 'Groundwater <br /> 'r Petroleum hydrocarbons in groundwater were detected in grab samples collected from borings <br /> SBI, SB2, SB3, SB4A, and SB6 and in wells MW-2 and MW-3. TPHg was detected in <br /> groundwater from borings SB2, SB4A, and SB6 and in wells MW2 and MW3. Concentrations <br /> ranged from 80 ppb (MW3) to 67,000 ppb (SB2). Benzene was detected in these same borings <br /> and wells at concentrations ranging from 38 ppb (MW3) to 2,200 ppb (SB2). Only toluene <br /> ` was detected in the groundwater from borings SBI and SB3 at concentrations slightly greater <br /> than the method detection limits. <br /> MTBE was detected in the groundwater from boring SB3 (3.5 ppb) and in monitoring wells <br /> MW2 and MW3 (7.6 ppb and 1.2 ppb, respectively). These results were confirmed by <br /> additional analysis of the samples by EPA method 8260. <br /> Figures 5 and 7 show the estimated lateral extent of TPHg and benzene concentrations in <br /> groundwater during the subsurface investigation and the third quarter 1996 monitoring event. <br /> ( As indicated on Figure 5, the plume of TPHg is north and northwest of the former location of <br /> LN wA951221PIumcrpt 10 <br /> SMTH <br />