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°jl u . 30 April 2005 AGE-NC Project No 96-0232 Page 7 of 9 the result of biological interference 4.0. CONCLUSIONS Based on the initial site conceptual model, AGE previously interpreted the results of all work completed to indicate that historically,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 westward through 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 Flag City Chevron MTBE-impacted ground water was interpreted to be between 25 feet bsg and 45 feet bsg Relative to the inferred source area near the Flag City Chevron UST area (EW-1), the Flag City Chevron plume previously extended westward for approximately 200 feet, where vertical migration appeared to have reached depths as great as 75 feet bsg (MW-11B), the maximum westward extent of the Flag City Chevron plume was most likely in the . area of the former Rocky's Restaurant domestic drinking water well (RDW-1), where the plume appeared to converge with that of a Three B's Truck Plaza MTBE ground water plume Figures 8, 9 and 10 depict two, distinct MTBE-impacted ground water plumes that previously converged near the vicinity of the former Rocky's Restaurant domestic well RDW-1 Recently,a third,distinct MTBE ground water plume has been defined north-northeast of Flag City Chevron in First Water Zone on Banner Avenue (Figure 8), this third plume extends through the First Water Zone at the McDonald's Restaurant,to Second Water Zone near the Flag City Chevron UST/fuel dispenser areas(Figure 9) Analytical results from the March 2005 quarterly ground water monitoring event indicated the highest concentrations of on-site MTBE occur in the Second Zone sample collected from MW-8A at 400 µg/1 (Figure 9) Based on this current data, and based on previous ground water elevation data collected during the Flag City Chevron investigation (I e induced ground water depression in the areas of ground water pump-and-treat extraction), the migration of the third MTBE-impacted ground water plume would explain the consistent MTBE- impact at well MW-8A between March 2002 and December 2004 AGE suspects this third MTBE- impacted ground water plume was influenced by the ongoing Flag City Chevron pump-and-treat ground water extraction activities, the third MTBE-impacted ground water plume appears to have been drawn onto Flag City Chevron property and towards the ground water extraction induced cone of depression The migration of the third plume is further substantiated by the P-36, P-37 and P-38 grab ground water samples collected in First Zone and Second Zone (October 2002) that were previously non detect for MTBE A significant detection of MTBE was observed from Flag City Chevron well MW-2 during Advanced GeoEnvironmental,Inc