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15 January 2002 AGE-NC Project No 96-0232 Page 15 of 16 I 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-2, MW-4, MW-6 at concentrations between 3 ,ug/l and 80 ug/l and Flag City Chevron wells MW-7,MW-12A and MW-13A at concentrations between 42 ug/1 and 6 4 ug/1 which suggest the possibility of separate MTBE plumes being pulled toward domestic water wells RDW-1 and DW-I (Figure 7) Gfound 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, however ground water ielevations did show slight increases during May 2000, December 2000,March 2001 and December 2001 monitoring events (Appendix I) ' Figures 10 and 11 depict the approximate extent of MTBE-impacted ground water beneath the site in cross sectional views C-C' and D-D', Figures 7, 8 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-I 1A,MW-13A and Three B's Truck Plaza wells MW-1,MW-4 and MW-6 to be located within dissolved MTBE-impacted and or TPH-impacted plumes The vertical extent of impacted ground water on-site appears to he between 15 feet bsg (estimated depth to ground water) and 50 feet bsg in the area of MW-I 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 previously detected in the Primary Aquifer(MW-9C),but were non-detect in water samples collected in December 2001 Going off-site toward the west,the plume may extend to as much as 75 feet bsg approaching the area of MW-I IB, near Rocky's Restaurant domestic well (RDW-1) where the underlying fine-grained sedimentary units may thin and pinch out, low concentrations of MTBE were detected in Primary Aquifer(MW-11D) 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 uncertain at this time Contaminants in First Zone ground water at MW-12 and MW-13 include TPH-g,TPH-d,TPH- mo, benzene, toluene, and MTBE, which suggest that most of the contaminants are from a source rother than the Flag City plume It is not known if the suspected plumes are co-mingled in the area between Three B's Trick 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 the Flag City Chevron UST area(EW-1), the extent of the Advanced GeoEnvtronmental,Inc