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29 October 1998 ` AGE-NC Project No 98-0448 Page 8 of 9 _ 4.0. SUMMARY AND CONCLUSIONS " Based upon data collected between July and September 1998, AGE concludes IM1 • In August 1998, ground water was inferred to be flowing generally southwest at a calculated gradient of 0 009 ft/ft, or approximately 69 feet per mile (Figure 9), in September 1998, ground water was inferred to be flowing generally southwest at a calculated gradient of 0 015 ft/ft Due to the low gradient at the site, slight variations in ground water measurements or changes of recharge/discharge of the local ground water could greatly modify ground water flow direction The low gradient at the site implies that ground water is moving slowly • TPH-g was detected at concentrations ranging between 160,ppb and 140,000 ppb from ground water monitoring wells MWA, MW-2, MW-4A, MW-413 and MW-6 (Table 4) • Laboratory analysis of ground water samples indicates that the greatest concentrations of dissolved petroleum hydrocarbons is located near wells MW-2 and MW-4 (Figure 11) • Laboratory analysis reported that none of the fuel oxygenates were detected above laboratory reporting limits from selected soil or ground water samples (Tables 1 and 4) • Field observations and laboratory data indicate that petroleum hydrocarbon-impacted soil is limited to depths between 20 and 55 feet bsg in the area containing MW-4 The estimated extent of petroleum hydrocarbon-impacted soil is illustrated in cross sectional view in Figures 12 • Field observations and laboratory data suggest that the impacted ground water beneath the site appears to have taken a relatively narrow, elongated oval shape (Figure 11) • The dissolved TPH-g plume appears to be constrained north, east and west of the current network of ground water monitoring wells Laterally,the dissolved plume appears to extend slightly south of MW-6 Based on the guide How to Evaluate Alternative Cleanup Technologies For UST Sites (October 1994) published by the United States Environmental Protection Agency (EPA) _ Office of USTs,the two most important factors that determine the effectiveness of SVE are ' permeability of the soil and volatility of the contaminant The guide further states that intrinsic permeability between the magnitude of 10 2 and 10'g and general volatility for gasolmes are generalfy'adequate for Soil Vapor Extraction (SVE)technology (Exhibit II-6 Intrinsic Permeability And SVE Effectiveness) Based on information gained through fate evaluation laboratory'analysis, the average permeability at the site was between 2 X 10` (MW-4 at 25 feet bsg) and 3 X 10 8 (MW-4 at 45 feet bsg) Results of the fate evaluation laboratory analysis indicated permeability conditions at the site are adequate for SVE • An unidentified faint to intense odor was noted in soil sample duplicates collected from soil' Advanced GeoEnvironmental,Inc