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I SS 11 y ! i" 11 November 2004 AGE-NC Protect No 02-0962 i Page 12 of 14 l 1 r, subsurface as described below The,site surface is essentially flat land that is developed into a truck and auto plaza(Figure 2) The majority of the ground surface is covered by an asphalt or concrete cap In general,a clayey silt layer i ranging from surface grade to approximately 30 feet bsg underlies the assessed portion of the property(vadose zone&HU 1) Beneath the clayey silt layer is a fine-grained layer consisting of silty i sand to'fine sand (HU2),which is encountered approximately from 30 feet bsg to 38 feet bsg HU2 has the characteristics of an aquifer, or the water table Beneath the silty sand to sand layer are alternating layers of stiff, fine-grained soils and sandy soils i The stiff fine grained layers act as confining layers,retarding the vertical migration of contaminants The sandy layers act as migratory flow units allowing contaminants to vertically and laterally migrate ifrom the source A geologic cross section is provided on Figure 4 During site assessment activities in July and August 2004, saturated soil or the capillary fringe was ' first encountered at approximately 25 feet to 30 feet below bsg Based on information from quarterly monitoring events performed by AGE at the adjacent Nomellini Construction Company, ground water flow is generally toward the north to northeast However,this maybe greatly modified by local recharge and discharge patterns Site assessment activities to date defined two areas where soil is impacted by concentrations of ' petroleum hydrocarbons The maximum petroleum hydrocarbon concentrations(110 mg/kg TPH-d) were detected adjacent to the former piping sample location P13, at 15 feet bsg in soil probe boring B3 (Figure 2) Petroleum hydrocarbons were also detected at a concentration of 12 mg/kg in the soil ' sample collected from boring B7 at 30 feet bsg, adjacent to piping sample P7 Soil samples collected at 60 and 90 feet bsg from boring CPT1 were impacted by petroleum hydrocarbons TPH-g was detected at concentrations of 2 1 mg/kg(CPT 1-60) and 6 3 mg/kg(CPT 1-90), TPH-d was detected at a concentration of 110 mg/kg in CPT 1-90 ' Site assessment activities to date defined an area where ground water is impacted by high concentrations of petroleum hydrocarbons The highest petroleum-hydrocarbon concentrations, up to 2,200,000 µg11 TPH-d,were detected in grab ground water samples adjacent to the former piping ' sample location P13 Petroleum hydrocarbons, up to 190,000 µg/l, were detected in grab ground water samples j ust north of dispenser D 1(Fzgure 2) MTBE was detected in minor concentrations just north of dispenser sample D7 Ground water,was not impacted below 35 feet bsg Ground water samples collected from the ground water monitoring wells defined the dissolved plume at the northern edge of the dispenser islands ' Based on AGE's interpretation of the available data,the initial release(s)of petroleum hydrocarbons . occurred from the former,dispensers and associated piping prior to their removal in 2003 Once ' Advanced GeoEnvironmental