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30 October 2004 AGE-NC Project No 96-0232 Page 12 of 14 5.0. CONCLUSIONS AGE interpreted the results of all work completed to indicate that a Flag City Chevron unauthorized release of MTBE occurred in the areas of the fuel dispensers,UST pit and/or storm drain,which then migrated through and along the First Zone and upper Second Zone to the area of the former Rocky's Restaurant domestic water well, at which point it may have migrated vertically through the Rocky's Upper, Secondary Aquifer and Primary Aquifer Zones The vertical extent of MTBE-impacted ground water at the Flag City Chevron site has previously been interpreted to be between 25 feet bsg and 45 feet bsg(Figure 10) Relative to the inferred source area near the Flag City Chevron UST area (EW-1), the Flag City Chevron plume may have previously extended approximately 200 feet to the west at depths as great as 75 feet bsg(MW-11 B), the maximum westward extent of the Flag City Chevron plume may be in the area of the former Rocky's Restaurant domestic dunking water well (RDW-1), where the plume appeared to be co- mingled with the Three B's Truck Plaza plume Figures 8, 9 and 10 depict Flag City Chevron wells EW-4, EW-5, EW-7 through EW-10, MW-8, MW-9, MW-11 and Three B's Truck Plaza wells MW-1,MW-2,MW-4,MW-6 and MW-8 through MW-1 i to be located within two,distinct MTBE- impacted ground water plumes that previously converged near the vicinity of the former Rocky's Restaurant domestic well RDW-1 AGE estimates the arithmetic average concentration of MTBE in ground water extracted between 15 June 2004 and 17 August 2004 at 47 µg11 During this time, the volume of water processed through the ground water pump and treat system was recorded at 885,468 gallons, yielding 0 35 pounds ofMTBE(equivalent to 157 grams)from the plume of impacted ground water(Appendix C) Analytical results from the September 2004 quarterly ground water monitoring event indicate that the highest concentrations of on-site MTBE occur in the Second Zone sample collected from MW-8A at 220 gg/l(Figure 9) During the last eleven consecutive quarterly ground water monitoring events (since March 2002),MTBE concentrations observed from MW-8A have fluctuated between 4 7 gg/l and 900 gg/l Based on the data collected in May, June and September 2004 from well MW-19, it appears that a third,distinct MTBE-impacted ground water plume is present north of the Flag City Chevron in the area of well MW-19 (Figure 8), offsite, the plume is most prevalent in the First Zone, with decreasing concentrations observed in the Second Zone hydrogeologic units Based on this current data, and based on previous ground water elevation data collected dunng the Flag City Chevron investigation(i e induced ground water depression in the areas of ground water extraction),it would appear that this third MTBE-impacted ground water plume could explain the recent phenomena of MTBE-impact being detected at Flag City Chevron well MW-8 following nine consecutive quarters of being non detect i Advanced CeoEnvironmental,Inc