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1 29 March 2004 AGE-NC Project No. 97-0327 tPage 6 of 12 ' Hydrogeologic Unit 1 -Located from 60 feet bsg to the maximum total depth of the borings, consists primarily of permeable to semi-permeable, fine to medium sand and silty sand with limited minor fine grained material; a slight westward dip in Hydrogeologic Unit 1 is ' evident. The hydrostratigraphic model presented is interpretational and will be modified as additional data ' is collected. 4.0. PETROLEUM HYDROCARBON DISTRIBUTION IN SOIL ' To date, a total of 58 soil samples have been collected during the investigation and analyzed for petroleum constituents; analytical results detected TPH-g at concentrations between 1.3 mg/kg and 3,000 mg/kg, TPH-d at concentrations between 2.8 mg/kg and 12,000 mg/kg, various BTEX compounds at concentrations up to 0.069 mg/kg benzene,7.6 mg/kg toluene,32 mg/kg ethylbenzenLe� t and 290 mg/kg xylenes, and MTBE at a maximum concentration of 0.89 mg/kg in 24 of the 58 samples analyzed (Table 1). The vertical e)t.eof gasoline- and diesel-impacted soil has been modeled to extend to maximum depths of 45;�fe'et bsg (Figures 5 through 8). The lateral extent of ' • petroleum impacted soil is mapped as an elongated, narrow, northeast-trending plume, generally defined to the northwest and southeast,but undefined toward the northeast and southwest (Figures ' 9 and 10). ` Y►� p S N ' 4.1. VADOSE ZONE PETROLEUM-IMPACT Based on depth to ground water measured between February 2000 to September 2003, water level ' during this period has ranged between 45 and 60 feet bsg. Therefore, soil samples collected from 45 feet bsg or less could be considered as representative of vadose zone conditions. Other than the UST removal soil samples,the majority of vadose-zone petroleum hydrocarbon-impacted soil was ' encountered between 40 and 45 feet bsg (e.g., borings MW-2, MW-3, P-6, P-8, P-10 and P-12); TPH-g concentrations were as high as 340 mg/kg, TPH-d concentrations were as high as 3,300 mg/kg, BTEX compounds were as high as 0.069 mg/kg benzene, 5.4 mg/kg toluene, 3.8 mg/kg ' ethylbenzene and 20 mg/kg xylenes, and MTBE concentrations were as high as 0.89 mg/kg. Y 4.2�A-=�=SME-AR-ZONE PETROLEUM=IMPACT--=- ' Soil samples collected from within the zone of ground water fluctuation at between 45 and 62 feet bsg are representative of the smear zone. Significant smear-zone petroleum-impacted soil was • encountered at 45 feet bsg from borings MW-3, with TPH-g concentration at'68 mg/kg, TPH-d'