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(IV:ATC ASSOCIATES I NC . Based on the analytical results from soil samples, the lateral extent of soil contamination beneath the site appears to extend from the former UST locations north (downgradient) less than 100 feet as indicated by soil samples collected from boring MW-4. Soil samples collected from borings B1/MW-1, SBI, SB6, MW-4, and MW-5 appear to define residual petroleum hydrocarbon constituents in soil. The lateral extent of benzene contamination in the soil is shown on Figure 3. As indicated on Figure 3, the highest concentrations of benzene are present in soil north to northwest of the former location of the gasoline USTs, in the vicinity of MW-3. The eastern boundary of residual soil contamination has been estimated based on analytical soil data from borings SB1 and MW-4 located 40 feet east and 120 feet north-northeast from the former USTs, respectively, and on a consistent groundwater gradient flow direction to the north-northwest. It is noteworthy to mention that MTBE was not detected in any of the soil samples analyzed above laboratory detection limits by EPA methods 8020 or 8260. Furthermore, the highest concentration of benzene in soil detected during the various subsurface investigations was only 15 milligrams per kilogram (mg/kg). This sample (SB3-9.0) was collected from soil boring SB3/MW-3 located approximately 60 feet downgradient of the former USTs at a depth of 9 feet bgs. No benzene was detected in this boring's underlying soil sample at 21.5 feet bgs. Utilizing the areal distribution pattern of benzene as shown on Figure 3, the soluable mass of benzene was calculated. The total soluable mass for benzene was estimated to be 13.63 Kg. Assumtions and calculations are included in ATC's Additional Site Evaluation and Request for No Further Action, dated June 27, 2000. Groundwater Based on the analytical results from groundwater samples collected from the on-site monitoring wells in June 1999, and from grab groundwater samples collected from borings SB 1 through SB7 on September 24 and October 2, 1996, the lateral extent of groundwater contamination beneath the site appears to be essentially defined. The dissolved hydrocarbon plume appears to extend from the former UST locations north and northwest at a distance less than 160 feet. The groundwater sample collected from MW-4, located approximately 100 feet downgradient of the former USTs, contained only benzene at a concentration of 1.7 ug/L. The previous March 1999 water sample collected from MW-4 in did not detect the presence of benzene above the laboratory method detectection limit of 0.05 ug/L. The estimated lateral extent of benzene impacted groundwater is shown on Figure 4. As indicated on Figure 4, the highest concentrations of benzene are present in groundwater north to northwest of the former location of the gasoline USTs. Well MW1 and borings SBI and SB7 define the extent of contamination to the south, although directly south of boring SB6 the extent is inferred. `.• The extent of dissolved contamination to the north is defined by borings SB3 and MW-5. The extent of contamination to the west is defined by MW-6. The eastern boundary is inferred based w:\17861\reports\modeling.doc 4