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30 April 2005 AGE-NC Project No 95-0141 IPage 8 of 10 I samples collected from wells MW-1 through MW-9, MW-11B and EX-1 at concentrations as high as 300,000 µg11 TPH-g, 17,000 µg/1 benzene, 40,000 µg/1 toluene, 5,500 µg/1 ethylbenzene and 29,700 µg/1 xylenes With the exception of well EX-1 the BTEX concentrations have been declining at the site, the concentrations of BTEX compounds have been stable in EX-1 At the present time the shallow (HU2) impacted ground water plume is laterally defined in all directions except towards at the eastern edge of the property The intermediate(HU3)ground water plume is defined west and immediately northwest of the tank pit but is undefined in all other directions The vertical extent of impacted ground water 1s somewhat defined in the apparent down- gradient direction by well MW-13 The vertical extent of dissolved impacted groundwater at the source area is not well defined and previous contamination detected at CPT 1 has not been confirmed Based on AGE's interpretation of the available data,the initial release(s)of petroleum hydrocarbons occurred from the former UST prior to Its removal in 1989 Once released to the subsurface, the contaminants migrated through the clayey silt/silt material to a vertical depth of approximately 15 ' to 3 5 ft bsg, at which point the contaminants encountered saturated sandy soil (HU2) and began to migrate laterally as well as locally vertically, lateral migration was dominantly towards the east and southeast,in the direction of ground water flow The vertical migration continued through the sandy and fine grained materials of HU2 to the sandy material of HU3 Further lateral migration of contaminants occurred in all directions Then the contaminants appear to leave the adsorbed phase and become dissolved in the ground water as they migrate to the stiff fine grained material of HU3 There does appear to be adsorbed contaminants bellow HU4 The dissolved contaminates continue to vertically migrate,below the source area,into sandy HU5 but the lateral migration does not appear Ito extend beyond this area 5.0. SUMMARY AND CONCLUSIONS The findings of the Fourth Quarter 2004 site investigation event include the following ' On-site soil lrthology consists predominantly of silt to silty clay alternating with silty sand and sand layers A significant unit of sand to silty sand is present from approximately 50 feet ' bsg to 70 bsg,another very large sandy unit is present from approximately 90 feet bsg to 120 feet bsg The sand units possibly act as migratory pathways across the site TPH-g, BTEX, MTBE, D1PE, ETBE, TAME, TBA, 1,2-DCA, and EDB were not detected at or above Ilaboratory reporting limits in any of the analyzed soil samples • The vertical extent of petroleum hydrocarbon-impacted soil is defined southeast of the source area in boring MW-13, as hydrocarbon contamination was not detected in any of the analyzed samples Advanced GeoEnvironmental,Inc I