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1 i 07 March 2003 ' AGE-NC Project No 95-0141 Page 9 of 10 ' AGE has developed a preliminary s-bsurface model of the site hydrostratigraphy comprised of six informal zones,a vadose(unsaturated)zone and five hydrological units HU2 and HU4 ' consisted of sand and are characterized by low pore pressures, HU1, HU3 and HU5 are dominantly silt intervals with variable pore pressures that generally range from low to medium, these intervals may not be significant barriers to vertical contaminant migration ' TPH-g was detected in both grab ground water samples collected from. CPT-01 at concentrations of 13,000 micrograms per liter(gg/l) and 140,000 gg/l,respectively BTEX was detected in both samples at concentrations as high as 4,600 gg/l benzene, 16,000 µg/1 ' toluene,2,100 gg/l ethylbenzene and 11,000µg/1 total xylenes(CPT-01-113-117) 1,2-DCA was also detected in both samples at concentrations of 8 8µg/1 and 250µg/1,respectively and EDB was detected in the sample collected between 113 feet and 117 feet bsg at a ' concentration of 90µg/1 The vertical extent of impacted ground water has not been defined • TPH-g, toluene, ethylbenzene, and total xylenes were detected in the one soil sample ' (CPT 1-1-85) collected from CPT-01 at concentrations of 16 µg/l, 16 µg/l, 5 1 µg/1 and 24 µg/1, respectively No other analytes, including benzene, were detected in the soil sample The vertical extent of petroleum hydrocarbon-impacted soil has not been fully defined I At the time of the October 2002 ground water monitoring event, depths to ground water ranged from 21 03 feet to 22 15 feet btoc, ground water elevations at the site ranged from 13 25 feet (MW-9B) to 14 53 feet (MW-9B) below MSL (Table 1) The shallow ground ' water was inferred to flow generally toward the southeast, at a gradient of 0 004 foot/foot (Figure 5), the decn ground water was inferred to flow generally toward the southeast, at a gradient of 0 007 foot/foot (Figure 6) Wells MW-3 through MW-5 were "drowned", and may not yield samples fully representative of ground water conditions near the top of the saturated zone, where fuel hydrocarbons would be expected to have the greatest impact • During fourth quarter 2002,TPH-g was detected in ground water samples collected from six of the fifteen wells at the site at concentrations as high as 150,000 µg/1 TPH-g-impacted shallow ground water has been defined, TPH-g-impacted deep ground water has not been I defined toward the south, east and north (Figure 7) • During fourth quarter 2002,one or more BTEX constituent was detected in six of the fifteen wells ground water wells The benzene concentrations in all six wells exceeds the DHS's Maximum Contaminant Level (MCL) for benzene in drinking water The concentrations of toluene(36,000µg/1),ethylbenzene(4,000µg/1)and total xylenes(20,000 gg/l)in well EX-1 were significantly above their respective MCLS • Fuel oxygenates were not detected in any of the ground water samples collected during fourth quarter 2002 • During fourth quarter 2002, 1,2-DCA was detected in ground water samples collected from . eleven of the fifteen wells at the site at concentrations as high as 410 µg/1 (EX-1) and EDB was detected in the ground water sample collected from well EX-1 at a concentration of Advanced GeoEnvironmental,Inc