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1 ' 16 December 2002 i AGE-NC Project No 97-0300 ' Page 5 of 8 ' 5.0. ASSESSMENT OF HYDROCARBON-IMPACTED SOIL 1T1p3 Between August 1999 and June 200 ;ten so it borings(P-1 through P-7 and MW-1 through MW-3) ' were advanced at the site to investigate the extent of hydrocarbon-impacted soil in the vicinity of the former USTs The greatest concentrations ofpetroleum hydrocarbon-impacted soil were encountered in soil boring P-1 at a depth of 5 feet bsg and in soil boring P-3 at a depth of 10 feet bsg (Table 2), ' P-1 is located near the northwest corner of the former UST pit and P-3 is located along the southwest margin of the former UST pit (Figure 2) r ' General lithology is depicted in cross sectional view in Figures 11 and 12 Selected soil sample locations and the estimated extent of petroleum-impacted soil beneath the site are depicted in cross sectional view in Figures 13 and 14 The estimated distribution of adsorbed TPH concentrations are ' depicted in plan view in Figure 15, a generalized site conceptual model is depicted in Figure 16 When the data collected at the site is plotted in both plan view and cross sectional view,the apparent ' volume of petroleum impacted soil remaining beneath the site is approximately 770 cubic yards (Appendix D) ' A mass-volume calculation using the data collected during investigation of the former UST area, yields approximately 6 69 gallons of gasoline and 6 08 gallons of diesel in the remaining impacted soil at the site(Appendix D)`A short diameter of 36 feet, a long diameter of 63 feet and a height of ' 35 feet were used to estimate a coned elliptical volume of impacted soil (Figures 13, 14 and 15) An average concentration of 21 50 mg/kg was used to calculate the total volume of remaining gasoline and 2190 mg/kg to calculate the total volume of remaining diesel in impacted-soil 6.0. ASSESSMENT OF HYDROCARBON-IMPACTED GROUND WATER Three ground water rgonitonng wells(MW-1,MW-2 and MW-3)were installed at the site between 05 and 06 June 2002' and four ground water monitormg/sampling events have been performed ' between 16 June 2000 and 22 March 2001 to investigate the extent of hydrocarbon-imp acted ground water in the vicinity of the former USTs Durin &;8me,depths to groundwater from wells MW-1, MW-2 and MW-3 were measured between 4i 38 and 52 15 feet below the top of well casings ' Generally, ground water elevation at the site decreased approximately 9 feet between the June and September 2000 monitoring events,but increased approximately 8 feet between the September 2000 and March 2001 ground water monitoring events Ground water monitoring data in the area of MW-1, MW-2 and MW-3 indicated a ground water flow direction generally toward the south- southeast at gradients between 0 01 ft/ft and 0 003 ft/ft (Figures 6, 7, 8 and 9) Due to the low gradient at the site,slight variations in ground water measurements or changes ofrecharge/discharge of the local ground water could greatly modify the inferred ground water flow direction Ground . water elevation data are summarized on Table 3 Advanced GeoE nvi ron mental,Inc r I