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12 December 2006 <br /> • AGE-NC Project No 01-0827 <br /> Page 13 of 14 <br />' The subsurface soil stratigraphy consisted of fine-grained,sandy silt/clayey silt between the <br /> surface/bottom the former UST excavation and generally 20 feet bsg A medium to locally <br /> coarse sand and gravel cut/fills were observed at 20 feet to 30 or 35 feet bsg at the former <br /> UST excavation A fine-grained silt/clayey silt was observed between a depth of 30 feet and <br /> 60 feet bsg and a silty sand was observed at 65 feet bsg <br /> • Ground water elevations at the site have fluctuated between 9 and 34 feet below MSL since <br /> Iground water monitoring began in December 1988 The depth to ground water has been a <br /> low as 45 feet bsg and as shallow as 20 feet bsg Ground water flow has been consistently <br />' east-northeasterly <br /> • Distribution of petroleum hydrocarbon contaminants in soil and ground water indicated an <br /> initial release/s in the area of the former UST#1,which then migrated laterally and vertically <br /> through the upper silts into the more permeable sand layer between 25 and 30 feet bsg <br /> Vertically,except for very low concentrations of BTEX compounds beneath the former UST <br /> location, soil contamination does appear to extend below HU3 and the vertical extent of <br />' ground water contamination Is defined <br /> • The hydrocarbon impacted soil above the current water table depth and surrounding the <br /> former UST release area has been mitigated The residual adsorbed hydrocarbons,within the <br /> current HU2 unit, hydrostratigraphy bound, sould attenuate naturally <br /> • The plume of dissolved hydrocarbons surrounding the former UST release area has been <br />' reduced to low concentrations,only detected in one shallow well within the former UST area <br /> • The vertical and lateral extent of dissolved hydrocarbons are defined and declining <br /> 9.0. RECOMMENDATIONS <br /> Based upon petroleum hydrocarbon distribution patterns and migration pathways identified in the <br /> report, AGE recommends no further environmental remediation and the site should be considered <br /> for certified site closure, including the destruction of the on-site and off-site monitoring wells <br /> Advanced GeoEnvironmental,Inc <br />