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1 27 October 2003 AGE-NC Project No 98-0450 ' Page 5 of 17 • The greatest concentrations of TBA were detected in soil below the former USTs and in the area of the former northern dispenser island at depths o f 2 5 feet bsg to 35 feet bsg,in general ETBE was also detected below the former northern dispenser island j Prior to remediation,petroleum hydrocarbon impacts appear to extend south of the former UST area 1 and beneath the former fuel dispenser island The orientation of cross-section lines A-A' across the site is north to south,with the apparent ground water flow direction The subsurface soil profile and theinferred extent ofhydrocarbon-impacted soil are illustrated on cross-sections A-A' (Figure 3/3A) ' As shown on the cross sections,concentrations of TPH-g,and BTEX were detected for soil samples collected from approximately 15 to 45 feet bsg ' The mayor portion of the petroleum hydrocarbon impact appears limited to the silty clay unit ranging from approximately 15 to 40 feet bsg under the former USTs and 15 to 25 feet bsg below the former dispensers The degree of hydrocarbon impact vertically decrease by within the clay layer ranging ' from approximately 15 to 30 feet bsg Soil samples collected from within the water-bearing zone at 40 to 55 feet bsg, below the former USTs,had a minor hydrocarbon impact While soil at depths of 60 and 65 feet bsg had no detectable hydrocarbon impact ' Based on the inferred vertical and lateral extent of on-site petroleum hydrocarbon impact, it is estimated that approximately 2,000 cubic yards of impacted soil is present on-site An initial mass ' of adsorbed TPH was not generated However, a later calculation determined that the mass of adsorbed TPH-g was estimated to be 5,022 kilograms or 11,049 pounds,in the vadose and saturated ' soils (Appendix B) 2 3 4 Extent of Petroleum Hydrocarbon-Impacted Ground Water Information collected from the site over the past four years indicts that the ground water flow at the ' site is directed to the south The depth to ground water measured in site monitoring wells and soil borings ranged from approximately 45 to 55 feet bsg Analytical results of the ground water sample analyzed are summarized in Tables 3 and Table 4 • The plume of impacted groundwater is constrained on its northern edge by the grab ground ' water sample collected from soil boring SB2 _ • The plume of impacted ground water above 10 µg11 of benzene is constrained on its western ' edge of the former USTs by wells BMW-1, BMW-2 and BMW-3 1 Advanced GeoEovironmental,inc