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• 09 May 2002 AGE-NC Project No 96-0232 Page 16 of 18 8.0. CONCLUSIONS AGE Interpreted the results of all work completed to indicate that 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 December 2001 and March 2002, significant concentrations of dissolved MTBE were detected from Second Zone well MW-8A(screened 40 to 50 feet bsg)and confirmed by resampling the well in April 2002 Located between MW-8 and the UST area, intermediate well MW-4 continued to have no detection of MTBE,albeit screened in the First Zone Since initiation of ground water extraction activities at the site, ground water flow direction in the First and Second Zones has generally been Inferred to be towards the south-southwest, and it is not clear at this time why substantial MTBE is present in MW-8A after nine consecutive quarters of being non-detect Between December 2001 and March 2002,subtle MTBE decreases were reported in extraction wells EW-6, EW-9 and monitoring wells MW-7, MW-12A and MW-13A, conversely, subtle MTBE Increases were reported from monitoring wells MW-9A, MW-11A, MW-11B, MW-11D and extraction wells EW-4, EW-5, EW-8 and EW-10, the data Implies that the decreases maybe due to the overall MTBE mass reduction in First Zone, the increases at MW-9, MW-11, EW-4 and EW-5 may be due the well abandonment of RDW-1 which may have caused a rebound effect due to discontinued pumping activity at RDW-1 and/or may have intensified the pulling effect of ground water extraction activities of the MTBE plume towards the Flag City Chevron site AGE estimates the arithmetic average concentration of MTBE in ground water extracted between 01 January and 31 March 2001 was 27 µg/1 The total volume of waterprocessed through the ground water pump and treat system was recorded at 3,054,581 gallons (equivalent to 25,466,041 pounds) of water extracted yields 0 75 pounds of MTBE(equivalent to 340 grams)removed from the plume of impacted ground water(Appendix E), or approximately 4 9 grams per day Analytical results from the March 2002 quarterly monitoring event indicates the most intense on-site MTBE impact is in the First Zone near EW-4 (100 µg/1) and in the Second Zone near MW-8A(700 µg/1), the most intense off site MTBE impact is in the First Zone near MW-7 and Three B's Truck Plaza well MW-4 (41 µg11 and 83 µg/1, respectively), in the Second Zone well MW-11A (94 µg/1) and in the Rocky's Upper Zone well MW-11B (150 µg/1) It is not clear at this time why the Three B's Truck Plaza well MW-4 has consistently had greater MTBE-impact than that of intermediate well MW-7 Advanced GeoEnvironmental,Inc