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' 17 January 2006 AGE-NC Project No 97-0249 Page 7 of 8 Flag City Chevron well MW-17 at a concentration of 37 µg/1 (Figure 11) • The most intense on-site,Hydrogeologic Unit 3MTBE-Impacted ground water was reported from the area of Three B's Truck Plaza well MW-9B at a concentration of 15 µg/1,and from ' the area of Flag City Chevron wells MW-11 B,MW-15 and MW-18 at concentrations as high as 170 µg/l (Appendix A) ' • The highest off-site concentrations of dissolved MTBE were detected in monitoring wells toward the east and northeast, in water samples collected from Flag City Chevron wells MW-8A(560 pg/l,Hydrologic Unit 2),MW-19A(15 µg/l,Hydrologic Unit 1)and MW-20A ' (500 µg11, Hydrologic Unit 1) Off-site, MTBE-impacted ground water from Hydrologic Units 1 and 2 are depicted on Figures 10 and 11, respectively • Low concentrations of TAME and 1,2-DCA have been detected from wells MW-2, MW-3 ' and MW-8(A-C), suggesting that only a minor TAME-impact and 1,2-DCA-impact to ground water in Hydrologic Unit 1 is present at the site I ' • The lateral and vertical extent of the dissolved petroleum hydrocarbon plume is not known toward the northeast of Three B's Truck Plaza well MW-2, toward the south of Three B's Truck Plaza well MW-6 and toward the south of Flag City Chevron wells MW-16/17/18 lie (Figures 8 through 11) 1 5.0. RECOMMENDATIONS 1 Based upon the results of the third quarter 2005 investigation, AGE recommends • Continued quarterly ground water monitoring of wells MW-1 through MW-15 The 4`h quarter 2005 quarterly ground water monitoring event was performed between 27 and 29 December2005 and a report of findings is forthcoming, ' 0 Preparation of a site conceptual model An interim ground water remediation program should be implemented at the site as soon as possible ' to establish hydraulic controls,inhibit potential off-site migration of the contaminated ground water plume, and to protect the on-site domestic water from the on-site ground water plume Additional ' reasons for interim remediation include • the high concentrations of contaminants(i e BTEX and MTBE and 1,2-DCA) encountered ' at the site that are significantly above the DHS's MCLs Advanced GeoEnvironmcntal,Inc 1