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R10/71-51-IC 8 0 CONCLUSIONS AND RECOMMENDATIONS Four different areas were investigated in the performance of the SI These areas are the following o The location of the former underground fuel tanks o The location of the former waste tank o The washrack area And o Front of the shop building Completion of the SI revealed the following findings about these four areas o Gasoline-derived petroleum hydrocarbons including benzene, toluene, ethylbenzene, and xylenes are present in the soil and the groundwater underneath and within the vicinity of the location of the underground fuel tank o Oil and gasoline derived petroleum hydrocarbons and PCBs were not found in the former waste oil tank area At this location, chromium was detected below levels of concern o Gasoline-derived petroleum hydrocarbons and halogenated volatile organics were not found in the soil and groundwater within the vicinity of the wash rack area o Very low levels of gasoline-derived hydrocarbons including benzene, toluene, and xylenes in the soil and groundwater within approximately 50 feet south of the shop building were detected Halogenated volatile organics however were not found in the soil or groundwater Analysis of their spatial distribution horizontally and vertically suggests that the contaminants migrated generally downward from leaking tank(s) through a sequence of silty clay and silt to a sand unit that generally occurs at approximately between 50 to 60 feet below grade in the affected area Review of the zero concentration maps (for benzene, toluene, and xylenes taken together) suggest that the contaminated area, centered near the former fuel underground tank location, increase from an area of approximately 17,700 square feet from 5-foot below grade, increasing to approximately 24,000 square feet at 25-foot depth, maximizing to approximately 49,000 square feet at 45-foot depth, and then gradually decreasing to 46