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Appendix A - Site Background Information Former Fisco Warehouse Page 6 of 7 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 33feet to 62 feet bsg during the investigation); the direction of lateral migration was dominantly towards the northwest, in the preferred ground water flow direction. Significant petroleum-hydrocarbon impact to soil in the vadose zone is present in borings Bl, B3, B5, MW1, and MW2, in the area of the former USTs. TPH-g, TPH-d and MTBE are present at maximum concentrations of 14,000 mg/kg(B5-25), 12,000 mglkg(B3-10 and-15)and 1,100 mg/kg (131-30), 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 of petroleum-impacted 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. For additional information please refer to the AGE-prepared Interim Corrective Action Plan,dated 20 January 2005. SOIL VAPOR EXTRACTION REMEDIATION The soil vapor extraction (SVE) remediation system began operation on 19 January 2006 with a total of 3,451 lbs of total petroleum hydrocarbons quantified as gasoline(TPH-g)extracted since the system began operation. TPH-g concentrations were declining or below detection levels and appeared to be reaching an asymptotic plateau, therefore, on 30 May 2008,the SVE unit was taken off-line for an EHD-approved "rebound"period. On 27 October 2008, after approximately 5 months of SVE cessation,the SVE system was brought on-line for rebound testing to determine if hydrocarbon concentrations in soil vapor remained at or Advanced GeoEnvironmental,Inc