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• 30 July 2004 AGE-NC Project No 96-0232 Page 13 of 16 • The most intense Second Zone off-site MTBE-impacted ground water were detected from the area of Flag City Chevron wells MW-17 and MW-19B at concentrations as high as 87 µg/1 (Figure 9) Between the March 2004 and June- 2004 quarterly monitoring events, a significant MTBE decrease was reported at well MW-17, from 140 gg/1 to 87 µgll • The most intense Rocky's Upper Zone off-site MTBE impacted ground water were detected from the area of Flag City Chevron wells MW-11B and MW-18 at concentrations as high as 130 µg/l(Figure 10,Table 6) Between the March 2004 and June 2004 quarterly monitoring events,a significant MTBE decrease was reported at well MW-18,from 190µg/l to 130µg/1 • Low concentrations of TPH-d have been detected at various wells during previous quarterly monitoring events at Flag City Chevron During June 2004, a low concentration of TPH-d was detected in the water samples collected from well MW-12A AGE had previously asked McCampbell Analytical Laboratory to review the TPH-d sample chromatograms from MW-12A, the laboratory concluded that the low TPH-d detections from MW-12A did not have typical diesel characteristics,and that the detected chromatogram peaks were probably the result of biological interference 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 ofthe 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 Rocl y'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-11B), the maximum westward extent of the Flag City Chevron plume may be in the area of the former Rocky's Restaurant domestic drinking 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-11 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 Based on the new data (MW-19) collected in June 2004, 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 Advanced GeoEnvironmental,Inc