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. r <br /> 04 May 2005 , <br /> AGE-NC Project No 95-0142 <br /> Page 8 of 9 - - <br />' Based upon data collected from the site during the current and preceding ground water monitoring <br /> events, AGE concludes <br /> r - <br /> • During first quarter 2005, the ground water surface appears southeasterly at a hydraulic <br /> gradient of 0 0027 ft/ft However,there is the possibility that the ground-water flow pattern <br /> ` may be influenced by a difference in hydraulic heads from wells screened at two different <br /> depth intervals (between 25 feet and 60 feet bsg, and between 70 feet and 80 feet bsg) <br /> Compared to the fine-grained soils between 25 and 60 feet bsg,the interval between 70 and <br /> 80 feet bsg appeared more sand-prone,and may be associated with a different hydrogeologic <br /> unit <br /> • Dunng the March 2005 sampling TPH-g was detected in the sample collected from vapor _ <br /> well VW-4 at 460 µg11 Low concentrations of BTEX compounds were detected in same <br /> sample, however when analyzed by EPA Method 8260, only ethylbenzene was detected <br /> • During the first quarter 2005, the fuel additives MTBE was detected in monitoring wells, <br />' along with the first detection of TBA at the site, however, all monitoring wells are <br /> "drowned"and analytical data from these wells may not be representative of shallow ground <br /> I water conditions <br /> Historically,the highest concentrations of dissolved petroleum hydrocarbons were detected <br /> in shallow well VW-1, located in the area of former UST TK1-90, however, TPH-g and <br /> BTEX concentrations in the deep-screened well (MW-6) at TK1-90 have steadily declined <br /> to non-detectable levels <br />' MTBE has been detected in ground water samples collected from well MW-7 for seven <br /> consecutive monitoring events,and sporadically from well MW-5,the distribution of MTBE <br /> suggests that the MTBE plume has migrated laterally and vertically from the former UST <br /> location to wells MW-5 and MW-7 <br />' S.O. RECOMMENDATIONS <br /> Based upon the results of the remediation activities to date, AGE recommends <br /> 1 <br /> • Continuation of ground water remediation with a possible addition of extraction well EW-2 <br />' and vapor wells VW-2 and VW-4, and discontinue soil vapor extraction due to non-detect <br /> level of extracted hydrocarbons. <br /> • Continuation of the quarterly ground water monitoring program <br /> U Advanced GeoEnvironmental,Inc <br /> 1 <br />