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• 15 July 2002 AGE -NC Project No 96-0232 Page 19 of 21 Ground water elevations versus ground water monitoring dates (hydrograph) were plotted for monitoring wells MW -2, MW -6A and MW -6B, generally, all three plots depict an overall trend of decreasing ground water elevation from March 2000 to December 2001 and in June 2002, however ground water elevations did show slight increases during the May 2000, December 2000, March 2001, December 2001 and the March 2002 monitoring events (Appendix 1) Figures 19 and 20 depict the approximate extent of MTBE -impacted ground water beneath the site in cross sectional views C -C' and D -D', Figures 16, 17 and 18 depict the estimated extent dissolved MTBE -impact in plan view These figures depict Flag City Chevron wells EW -4, EW -5, EW -6, EW -8, EW -10, MW -7, MW -8A, MW -9A, MW -IIA, MW -11B, MW -11D and Three B's Truck Plaza wells MW -1, MW -2, MW -4 and MW -6 to be located within dissolved MTBE -impacted plumes The vertical extent of impacted ground water on-site appears to he between 12 feet bsg (estimated depth to ground water) and 50 feet bsg in the area of MW -1 and MW -9 (Figures 19 and 20) Impacted ground water in the area at 40 to 50 feet bsg in MW -9 is underlain by two thin fine- grained units (Problem Assessment Report, dated 19 June 2000) that appear to have retarded the downward migration of the MTBE Low concentrations of MTBE were previously detected in the Primary Aquifer (MW -9C), but have been non -detect in water samples for three consecutive sampling events Going off-site toward the west, the plume may extend to as much as 75 feet bsg approaching the area of MW -11 B, near the former Rocky's Restaurant domestic well (RDW -1) where the underlying fine- grained sedimentary units may thin and pinch out, low concentrations of MTBE have been detected in Primary Aquifer (MW -11D), screened at between 130 and 150 feet bsg Further westward from MW -11, the plume of water impacted by MTBE appears to extend beyond Three B's Truck Plaza well MW -4, with a vertical extent from possibly 12 feet bsg to possibly 75 feet bsg The full westward extent of the Flag City Chevron plume is uncertain at this time Contaminants in Fust Zone ground water at MW -13 include TPH-d and TPH-mo which suggest that the contaminants may be from a source other than the Flag City plume It is not known if the suspected plumes are co - mingled in the area between Three B's Truck Plaza wells MW -1 through MW -6 and Flag City Chevron wells MW -7, MW -11, MW -12 and MW -13, AGE has modeled them as separate plumes (Figures 16 and 17) Relative to the inferred source area near the Flag City Chevron UST area (EW -1), the Flag City Chevron plume appears to extend approximately 200 feet to the west at depths as great as 75 feet bsg (Figures 16 and 18), approximately 20 feet to the south at depths as great as 30 feet bsg (Figure 8), and approximately 80 feet to the east at depths as great as 30 feet bsg (Figures 16 and 18) The northern extent of the Flag City plume is uncertain at the present time because of the high concentrations of MTBE (up to 250 µg/l) detected in northernmost Flag City Chevron well MW -8 during the June 2002 monitoring event Advanced GeoEnvironmental, Inc.