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04 October 2005 <br /> AGE-NC Protect No 98-0432 <br /> Page 5 of 6 <br /> well Installation <br /> No petroleum hydrocarbon constituents were detected in any of the ground water monitoring wells <br /> during the last four monitoring events, conducted from October 2004 to July 2005, with the <br /> exception of low detections of TPH-g, ethylbenzene, and xylenes in well MW-8 in April 2005 <br /> (Table 4) Analytical results and field logs from the last ground water monitoring event, conducted <br /> on 28 July 2005, are included in Appendices B and C, respectively <br /> 5 1 PETROLEUM HYDROCARBON CONCENTRATION TRENDS <br /> Ground water monitoring wells MW-1 and MW-2 have been the most impacted at the site,laboratory <br /> analysis has reported TPH-g, TPH-d, and MTBE as high as 1,600 pg/l, 590 µg11, and 31,000 µg/l, <br /> respectively TBA was detected in well MWA in May 2000 at a concentration of 1,500 µg/l, <br /> ethylbenzene and xylenes were detected in well MW-8 in April 2005 at concentrations of 27µg/1 and <br /> 3 4 µg/l, respectively (Table 4) .27 Viii,/d C <br /> The concentrations of petroleum hydrocarbon contaminants in wells MW-1 through MW-8 have I <br /> • declined below detection limits between the Initiation of ground water monitoring in January 2000 <br /> and the present <br /> Trend analysis for MTBE in wells MW-1 through MW-8 shows concentrations declining to below <br /> detection limits since initiation of ground water monitoring (Appendix D) <br /> G.O. SUMMARY AND CONCLUSIONS <br /> Based upon a review of site assessment activities to date, AGE concludes <br /> • The majority of petroleum hydrocarbon-impacted soil appeared to be limited to the area near <br /> the former UST,designated T1 The highest petroleum hydrocarbon concentrations in soil, <br /> namely TPH-d, were detected in samples T1NW and T1 SE, collected in September 1998 <br /> �4L r000�1 phi.0.� <br /> • Based on to concentr tions of TPH-d in soil samples collected during the UST removal and <br /> over-excavation and the concentrations of MTBE detected in soil samples collected from the <br /> water bearing zone,AGE believes soil contamination is minimal due to the affinity of MTBE <br /> to dissolve and nugrate in ground water and due to the lack of adsorbed contamination above <br /> the current and past water table depths <br /> • Historically,petroleum hydrocarbon-impacted ground water has been detected consistently <br /> 17 <br /> only in monitoring wells MW-1 and MW-2 Wells MW-3 through MW-5 andMM -8 have <br /> • had only occasional detections of petroleum hydrocarbons through April 2005, petroleum <br /> Advanced GeoEnvironmentai,Inc <br />