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f ' 15 January 2002 AGE-NC Project No 96-0232 ' Page 14 of 16 ' During non-pumping penods,MTBE-unpacted ground water migrated from the well casing and/or filter pack laterally along the coarse-grained members of the lower hydrologic units ' Ground water extraction from the ground water extraction system on the Flag City Chevron site has pulled back some impacted ground water, lowering MTBE concentrations in ground water in the general extraction area, and has prevented additional lateral and vertical ' migration of the impacted ground water • Continued production of ground water from RDW-1 in combination with reduction of west- southwestward migration of impacted ground water has reduced the concentrations of MTBE to the lower hydrologic zones in the vicinity of RDW-1, however, RDW-1 can still serve as a vertical conduit for impacted ground water 1 ' 6.0 CONCLUSIONS AGE interprets the results of all work completed to indicate a Flag City Chevron release of �. hydrocarbons and MTBE occurred in the areas of the fuel dispensers, UST pit and/or storm drain, which then migrated through the First Zone and upper Second Zone to the Rocky's Restaurant domestic well, at which point it apparently migrated vertically to the Rocky's Upper, Secondary ' Aquifer and Primary Aquifer Zones Between September and December 2001, concentrations of dissolved MTBE decreased in samples ' from monitoring wells MW-1,MW-7,MW-9C,MW-11B,MW-13A and from extraction wells EW- 2, EW-5 and EW-6, the data implies that the decreases may be due to the overall MTBE mass reduction in First Zone and Second Zone ground water at the site ' Conversely, between September and December 2001, concentrations of dissolved MTBE slightly increased in wells RDW-1, MW-9A, MW-11A, MW-11D, MW-12A, EW-4, EW-9 and EW-10 ' which could be a rebound effect from selective extraction wells during a non-pumping period AGE estimates the arithmetic average concentration of MTBE in ground water extracted between ' 01 October and 31 December 2001 was 21 5 µg/l The total volume of water processed through the ground water pump and treat system was recorded at 2,043,809 gallons (equivalent to 17,039,235 pounds) of water extracted yields 0 36 pounds of MTBE (equivalent to 162 grams) removed from the plume of impacted ground water(Appendix D), or approximately 18 grams per day Analytical results from the December 2001 quarterly monitoring event indicates the most intense on- site MTBE impact is in the First Zone near EW-4 (53 ,ug/1), the most intense off site MTBE impact . is in Rocky's Upper Zone of MW-1113 (120 ,ug/1), which is probably influenced by the pumping tAdvanced GeoEnvironmental,Inc