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' 30 October 2003 i AGE-NC Project No 96-0232 Page 13 of 15 • The most Intense Second Zone off-site MTBE-Impacted ground water were detected from the area of Flag City Chevron well MW-17 and Three B's Truck Plaza wells MW-9A and MW-1 OB at concentrations of 13 µg/1 and less (Figure 9) Between the June and September 2003 quarterly monitoring events,a significant MTBE decrease was reported at well MW-17, from 140 µg/1 to 4 9 µg/1 • 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;ks high as 120 µg/1 (Figure 10, Table 6), significantly higher concentrations of MTBE have been reported from wells MW-15 and MW-18 during the previous quarterly monitoring events ' • Low concentrations of TPH-d have been detected at various wells during previous quarterly monitoring events at Flag City Chevron During September 2003, low concentrations of ' TPH-d were detected in water samples collected from wells MW-I IA and MW-12A, screened within the First Zone aquifer AGE had previously asked McCampbell Analytical 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 lie 5.0. CONCLUSIONS AGE interpreted the results of all work completed to indicate that a Flag City Chevron release of petroleum hydrocarbons and associated 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 ' Laboratory results from the third quarter 2003 analysis of water samples from the pump-and-treat system Indicate that, In general, MTBE concentrations were very low but stable, with slightly decreasing concentrations observed at extraction wells EW-1,EW-4,EW-5,EW-7 and EW-10 AGE estimates the arithmetic average concentration ofMTBE in ground water extracted between 25 June 2003 and 15 September 2003 at 18 µg/1 During this time, the volume of water processed through the ground water pump and treat system was recorded at 835,840 gallons (equivalent to 6,968,398 pounds), yielding 0 13 pounds of MTBE (equivalent to 59 grams) from the plume of impacted Iground water(Appendix D) In March 2003, AGE had observed a `spike' in MTBE concentrations at extraction wells EW-4, EW-5,EW-7 through EW-10,which may have been related to the failure of some of the site's UST primary product Imes and the UST sump to pass the annual `Lane and Leak Detector'test in January 2003 As a result of the `leaking lines', the Flag City Chevron upgraded the entire UST system(i e IAdvanced Geo Environmental Inc I