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28 November 2005 (�4 AGE-NC Protect No 96-0232 Page 6of8 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 and UST pit,which then migrated westward through the First Zone and upper Second Zone to the area of 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-11 B), 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 5), this third plume extends through the First Water Zone at the McDonald's Restaurant, to Second Water Zone at the Flag City Chevron UST/fuel dispenser areas (Figure 6) Analytical results from the September 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 560 µg/1 (Figure 6) Based on this current data, and based -an- 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 June 2005 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 Zane (October 2002) that were previously non detect for MTBE By March 2004, MTBE concentrations sampled from Flag City Extraction wells EW-1 through EW-10 all generally declined to either non-detectable(EW-1, EW-2,EW-3,EW-6,EW-7,EW-10) or near non-detectable levels(EW-4,EW-5, EW-8, EW-9), which also could be argued were levels that could potentially warrant a site closure However, a general trend of significant `spikes' was Advanced GeoEnvironmental,Inc