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' 24 September 1999 ' AGE-NC Project No. 96-0232 Page 2 of 12 ' at approximately 8 feet below site grade (bsg). Soil and ground water samples were collected from the sidewalls of the excavation and submitted to a Department of Health Services (DHS) certified ' laboratory for analysis of petroleum hydrocarbons. Dissolved total petroleum hydrocarbons quantified as gasoline and diesel (TPH-g and TPH-d) were detected in grab ground water samples at concentrations ranging as high as 18,000 micrograms per liter(µg/1). Dissolved benzene,toluene, ' ethylbenzene and xylene(BTEX compounds)were detected at concentrations ranging as high as 860 µg/l. TPH-g was detected in a soil sample (L3B) beneath the former product piping at a concentration of 1.5 milligrams per kilogram (mg/kg); BTEX compounds were detected from L313 t at concentrations ranging as high as 0.18 mg/kg. TPH-d was not detected in any soil samples. Analytical results are summarized in Tables 1 and 2. ' 2.3. PREVIOUS INVESTIGATION ' The following is a brief summary of site assessment activities: ' a In May 1991,three ground water monitoring wells(MW-1,MW-2 and MW-3)were installed at the site to investigate petroleum hydrocarbon impact near the former UST area. Dissolved petroleum hydrocarbons were not detected in initial ground water samples collected from ' MW-1 though MW-3,however benzene was detected in samples collected from wells MW-1 and MW-3 at concentrations as high as 9.4µg/l during subsequent sampling events; ground water depths were initially recorded from wells MW-1, MW-2 and MW-3 at approximately ' 12 feet bsg with a general ground water flow direction toward the north. • In July 1996, one ground water monitoring well (MW-4) was installed at the site to further ' assess petroleum hydrocarbon impact. Laboratory analysis of soil samples collected from MW-4 did not detect TPH-g, TPH-d, BTEX or compounds. However, dissolved methyl tertiary butyl ether (MTBE) was detected in the initial ground water sample at a ' concentration of 0.74 µg/l; ground water depths were recorded from wells MW-I through MW-4 at approximately 15 feet bsg with a general ground water flow direction toward the southwest. Analytical results are summarized in Tables 3 and 5. ' • In August and September 1997, five soil borings (P-1 through P-5) were advanced to maximum depths of 70 feet bsg at the site to further assess petroleum hydrocarbon-impact. ' MTBE was detected from a soil sample collected from P-1 (35 feet)at a concentration of 140 mg/kg. Dissolved MTBE and tert-butanol (TBA) were detected from grab ground water samples collected from P-I and P-5 at concentrations ranging as high as 410 µg/1. t • In June 1998,three ground water monitoring wells(MW-5,MW-6 and MW-7)were installed at the site to further assess the petroleum hydrocarbon impact. Laboratory analysis of soil ' samples collected from MW-5, MW-6 and MW-7 did not detect TPH-g, TPH-d, BTEX or Advanced GeoEnvirnnmental,Inc. 1