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F 1'1 November 2004 AGE-NC Project No 02-0962 Page 13 of 14 v w' released to the subsurface, the contaminants migrated through and/or adhered to the clayey silt material to a vertical depth of approximately 20 feet bsg, at which point the contaminants encountered permeable silty sand to fine-gr`amed material (HU1) and began to migrate laterally, Tateral migration was dominantly towards the north to northeast, in the direction of ground water i flow bA. SUMMARY AND CONCLUSIONS , Based upon data collected during this subsurface investigation, AGE concludes the following • Clay and silt occurred under most of the site, with the exception of an apparently laterally i continuous sand unit between 25 feet and 35 feet bsg Ground water occurred at approximately 25 and 30 feet bsg during the August 2004 site assessment r • Significant concentrations of both TPH-g and TPH-d were detected in grab ground water samples collected in the northern dispenser area The lateral extent of TPH-g and TPH-d contamination in ground water is not yet defined to the north and west of the release The � . vertical extent of petroleum hydrocarbon contamination In ground water has been defined in boring CPT1 I The lateral extent of TPH-g and TPH-d contamination In soil Is defined in all directions with the exception of the area south of boring B7 The vertical extent of TPH-g and TPH-d contamination in soil has not been defined,however the presence of very low concentrations , of TPH in soil samples collected from depths near and'surrounding non-detect grab ground water samples is inconclusive, due to the lack of dissolved contamination • ,Depth to ground water at the site averaged approximately 2131 feet bsg on 09 August 2004 IGroundwater elevation in the monitored area ranged from 9 37 feet to 9 38 feet below MSL Flow direction ,was inferred 'to be toward the northeast under a nearly flat gradient of ' approximately 0 0041 ft ft <, • Nor e of the constituents of concern were detected in ground water samples from any of the - m three ground water monitoring wells µl { 1 I T •' No other target analytes were detected at or above laboratory detection limits in either the soil or "grab" ground water samples analyzed This data-suggests that the initial mass of , hydrocarbon impacted soil detected during the piping and dispenser upgrades was minor in, ' nature The clayey and silty nature of the soil may have retarded the migration of hydrocarbons through the vadose zone r Sr Advanced GeoEnvironmental,Inc � s , , r