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30 January 2004 AGE-NC Project No 96-0232 Page 13 of 15 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 fourth 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 at the pump-treat influent AGE estimates the arithmetic average concentration of MTBE in ground water extracted between 15 September 2003 and 09 December 2003 at 24 lig/l During this time,the volume of water processed through the groundwater pump and treat system was recorded at 1,109,431 gallons (equivalent to 9,249,326 pounds), yielding 0 24 pounds of MTBE (equivalent to 109 grams) from the plume of impacted ground 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 primaryproduct lines and the UST sump to pass the annual `Lane and LeakDetector'test in January 2003 As a result of the `leaking lines',the Flag City Chevron upgraded the entire UST system(i e replacement of fuel dispensers and pans, product piping, secondary containment piping and UST sumps) during May 2003 Since then, the MTBE dissolved plume appears to have generally stabilized Analytical results from the December 2003 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 400µgd(Figure 9) The MTBE concentration reported in sample MW-8A is a significant decrease from the March 2003 concentration of 900 µg11,however,an increasing or decreasing trend of MTBE concentrations has not been established The vertical extent of MTBE-impacted ground water at the Flag City Chevron site is interpreted to be at 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 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-2 through EW-9,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-12 to be located within two,dissolved MTBE-impacted plumes that converge near the vicinity of the former Rocky's Restaurant domestic well RDW-1 The Flag City Chevron plume appears to extend less than 130 feet to the south (based on previous detection of MTBE at MW-6B) at depths as great as 48 feet bsg, and at least 60 feet to the east (between EW-9 and MW-2) at depths as great as 35 feet bsg (Figure 8) The northern extent of the Flag City plume is uncertain at the present time because of the high concentrations of MTBE(up to Advanced GeoEnvironmental,Inc