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' 15 October 2001 AGE-NC Project No 96-0232 ' Page 16 of 17 ' on-site MTBE impact is in the First Zone near EW-5 (35 µg/1), the most intense off site MTBE impact is in Rocky's Upper Zone of MW-11B (130 µg/1), which is probably influenced by the pumping operation of RDW-1 and is beyond the immediate influence of the Flag City Chevron ' ground water pump-and-treat remediation system Significant concentrations of MTBE were quantified west of the site in the area of Three B's Truck ' Plaza wells MW-1, MW-4, MW-6 at concentrations between 4 7 µg/l and 110 µg/1 and Flag City Chevron wells MW-7 and MW-13A at concentrations between 23 µg/1 and 47µg/1 which suggest the possibility of separate MTBE plumes being pulled toward domestic water wells RDW-1 and ' DW-1 (Figure 7) 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 depicted a trend of decreasing ground water elevations from May 2000 to September 2001, however ground water elevations did show an mcrease from August 2000 to March 2001 (Appendix 1) Figures 10 and 11 depict the approximate extent of MTBE-impacted ground water beneath the site in cross sectional views GC' and D-D', Figures 7, S and 9 depict the estimated extent dissolved MTBE-impact in plan view These figures depict Flag City Chevron wells MW-1, MW-7, MW-9A, MW-11A,MW-13A and Three B's Truck Plaza wells MW-1,MW-4 and MW-6 to be located within dissolved MTBE plumes The vertical extent of impacted ground water on-site appears to he between 15 feet bsg(estimated depth to ground water) and 50 to 60 feet bsg in the area of MW-1 and MW-9 (Figures 10 and 11) 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 detected in Primary Aquifer (MW-9C) Going off-site toward the west,the plume may extend to as much as 75 feet bsg approaching the area of MW-11B, near Rocky's Restaurant domestic well (RDW-1) where the underlying fine-grained sedimentary units may thin and pinch out Further westward from RDW-1, 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 15 feet bsg to possibly 75 feet bsg The full westward extent of the Flag City Chevron plume is un at this time Contaminants in First Zone ground water at MW-12 and MW-13 include TPH-g,TPH-d,TPH-mo,benzene,toluene,xylene,MTBE and 1,2-DCA,which suggest that most of the contaminants are 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 10 and 11) Relative to the inferred source area near MW-1, the extent of the Flag City Chevron plume appears Advanced GeoEnvironmental,Inc I