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' 09 May 2003 AGE-NC Project No 96-0232 ' Page 15 of 16 ' to be located within two,dissolved MTBE-impacted plumes that converge in the area of the former Rocky's Restaurant domestic well RDW-1 ' The vertical extent of MTBE-impacted ground water at the Flag City Chevron site appears to he between 12 feet bsg(estimated depth to ground water)and 55 feet bsg(Figures 10 and 11) Relative to the inferred source area near the Flag City Chevron UST area (EW-1), the Flag City Chevron ' plume appears to have extended approximately 200 feet to the west at depths as great as 75 feet bsg (Figures 10 and 11), the full westward extent of the Flag City Chevron plume is uncertain at this time, although it appears that the Flag City Chevron and Three B's Truck Plaza plumes are co- mingled in the area between Three B's Truck Plaza well MW-4 and Flag City Chevron wells MW-11,MW-14 and MW-15 The plume extends approximately 130 feet to the south(MW-6B)at depths as great as 48 feet bsg, and approximately 60 feet to the east(between EW-9 and MW-2) at ' depths as great as 35 feet bsg (Figure 10) The northern extent of the Flag City plume is uncertain at the present time because of the high concentrations of MTBE (up to 900 µg/1) detected in northernmost Flag City Chevron well MW-8 during the March 2003 monitoring event It is not clear at this time why substantial MTBE isP resent in on-site well MW-8A after nine consecutive quarters(between May 2000 and December 2001)of being non-detect Since initiation fof ground water extraction activities at the site,First and Second Zone ground water flow direction in the area of MW-8 has generally been towards the south-southeast, and should draw on-site contaminants away from MW-8(Figure 5) The most intense MTBE detections were reported during the March 2002 and the March 2003 sampling events, which could be related to the seasonal high ground water levels observed at the site each year near March(Table 4) However,intermediate well MW-4, located between MW-8 and the UST area, have no detection of MTBE, albeit screened in the First Zone, and three soil bonngs (P-36 through P-38) advanced in October 2002 to assess the area near MW-8(Figure 2)did not detect MTBE in grab ground water samples collected from `First Water'and `Second Water' AGE has tentatively concluded that the MTBE detections in MW-8 is a separate dissolved MTBE plume(Figure 9) I AGE estimates the arithmetic average concentration of MTBE in ground water extracted between 05 December 2002 and 25'March2003 was 42 gg/1 During this time,the volume of water processed through the ground water pump and treat system was recorded at 2,871,250gallons (equivalent to I 23,937,611 pounds), yielding 0 86 pounds of MTBE (equivalent to 390 grams) from the plume of impacted ground water(Appendix D) IIn general, increased MTBE concentrations were reported in water samples collected at the pump- and-treat influent sampling port and at extraction wells EW-4,EW-7 and EW-8 during March 2003 AGE has been informed that in January 2003,some of the site's UST primary product hues and the UST sump located nearest to EW-7 did not pass the annual `Line and Leak Detector'test, and that the Flag City Chevron will not be operational during the month of May 2003 for upgrades to the IUST system (i a replacement of fuel dispensers and pans, product piping, secondary containment Advanced GeoEnvnronmental,Inc,