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• 08 March 2000 AGE-NC Project No 96-0232 Page 2 of 11 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(j.cg/l) Dissolved benzene,toluene, ethylbenzene and xylene(BTEX compounds)were detected at concentrations ranging as high as 860 ,ug/l TPH-g was detected in a soil samples beneath the former product piping at concentrations up to 1 5 milligrams per kilogram (mg/kg), BTEX compounds were detected in soil samples beneath the product piping at concentrations ranging as high as 0 18 mg/kg TPH-d was not detected in any soil samples 23 PREVIOUS INVESTIGATION The following is a brief summary of site assessment activities • 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/1 during subsequent sampling events, ground water depths were initialIy 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 the petroleum hydrocarbon-impact Laboratory analysis of soil samples collected from MW-4 did not detect TPH-g, TPH-d, or BTEX compounds However, dissolved methyl tertiary butyl ether (MTBE) was detected in the antral ground water sample at a concentration of 0 74 ,ug/l, ground water depths were recorded from wells MW-1 through MW-4 at approximately 15 feet bsg with a general ground water flow direction toward the southwest Analytical results are summarized in Tables 1 and 3 • 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 the petroleum hydrocarbon- impact MTBE was detected in 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-1 and P-5 at concentrations ranging as high as 410 ,ug/l Analytical results of soil samples are summarized in Table 1 • 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 fuel oxygenated compounds However, dissolved TPH-d was detected in the initial ground Advanced GeoEmironmental,Inc