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1 ' 20 January 2005 AGE-NC Project No 97-0343 ' Page 8 of 21 ' The soil profile beneath the site is composed dominantly of sands and silts from surface grade to approximately 96 feet bsg,and finer-grained silts and clays from 96 feet bsg to total depth of 134 feet bsg Figures 4 and 5 Illustrate subsurface geologic profiles at the site Boring logs are Included in ' Appendix A Since initiation of ground water monitoring in February 2000,depth to ground water measurements ' have fluctuated between a 33 feet btoc and 62 feet btoc (Table 1) The Inferred ground water flow direction generally has been towards the northwest(nine times)at gradients ranging between 0 001 ft/ft and 0 008 ft/ft, ground water flow was towards the south four times at gradients between 0 01 ' ft/ft and 0 05 ft/ft, and twice towards the east or northeast at gradients between 0 001 ft/ft and 0 04 ft/ft ' Releases of petroleum hydrocarbons occurred from the on-site USTs Once released to the subsurface,the contaminants migrated through the fine grained unit directly below the UST area to a vertical depth of approximately 15 feet bsg, at which point the contaminants encountered a more ' porous sand unit and began to migrate laterally as well as vertically The lateral migration was further Increased when ground water was encountered(which has been recorded at 33 feet to 62 feet bsg during the investigation), the direction of lateral migration was dominantly towards the northwest, in the preferred ground water flow direction I Significant petroleum-hydrocarbon impact to soil in the vadose zone is present in borings B1, B3, B5, MW 1, and MW2, in the area of the former USTs (Table 6) TPH-g, TPH-d and MTBE are present at maximum concentrations of 14,000 mg/kg (B5-25), 12,000 mg/kg (B340 and -15) and ' 1,100 mg/kg(B 1-30),respectively Most of the contamination appears to reside above the top of the fine grain layer, at approximately 50 to 55 feet bsg, currently the extent of the soil contamination is completely within the vadose zone ' The vertical extent of ground water is defined near the UST area by MW-8, ground water contamination does not extend below 90 feet bsg The lateral extent ofpetro Icum-imp acted ground water was defined by wells MW-4 through MW-7,but these wells are now intermittently dry With the exception of two detections of 1,2-DCA in well MW-4,petroleum hydrocarbons have not been detected in wells peripheral to wells MW-1 through MW-3, located in the UST area, since third quarter 2001 8.0 POTENTIAL IMPACT ON NEARBY SURFACE AND GROUND WATER Typically, ground water would represent the migration medium for contaminants over significant horizontal distances However, sites located in up-gradient or cross-gradient directions from the • subject property are not likely to be negatively impacted by the subject property In addition, first IAdvanced GeoEnvi ron mental,Inc