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31 August 2005 AGE-NC Project No 96-0232 Page 27 of 30 flow direction was typically inferred between east and southeast at a hydraulic gradient of 0 001 (Table 6, Appendix H) • The most intense on-site dissolved MTBE concentrations were historically detected adjacent the southwest corner of the UST area from wells MW-1, EW-1 and EW-2 as high as 5,700 pg/1 However, all three wells declined to either non-detect or near non-detect levels by September 2001 (MW-1 and EW-2) and September 2002 (EW-1) Based on plots of MTBE and ground water elevations versus time (Appendix J), an apparent trend of decreasing dissolved MTBE concentrations was evident on-site from monitoring wells MW-1, MW-2 and MW-4 between July 1996 and March 2005 • The most intense off-site dissolved MTBE concentrations were historically detected towards the west from well MW-13A(near Three B's Truck Plaza above ground storage tank area) at concentrations as high as 2,500 µg/1 (May 2000) and towards the north from well MW- 19A(Banner Avenue)at concentrations as high as 5,300 µg11(May 2004) An apparent trend of declining MTBE concentrations was evident from off-site wells MW-6A, MW-7, MW- 11(A and B), MW-12A, MW-13A and MW-19A, however, between December 2004 and June 2005,increased ground water elevations and increased dissolved MTBE concentrations were reported from First Zone well MW-2, from Second Zone well MW-8A and from • Rocky's Upper Zone well MW-15 No other trends were determined from ground water monitoring wells MW-1 through MW-20 • Ground water pump-and-treat remediation was performed at the site between November 2000 and August 2004, during this time, a grand total of 27,086,201 gallons of MTBE-impacted water was treated From the 27,086,201 gallons of treated ground water, a grand total of 13 33 pounds of MTBE was estimated to have been removed Laboratory analysis of influent pump-and-treat samples were initially as high as 1,000 pg/1 in November 2000, however, MTBE influent concentrations generally decreased below 100 µg11 by June 2001 and were detected below 13 µg/1 (maximum contaminant level) on five separate occasions in September 2001,March 2002,August 2002, September 2002 and November 2002(Table 2, Appendix K) • Laboratory analysis of ground water extraction well samples (EW-1 through EW-10) historically detected MTBE from all ten wells, the greatest MTBE concentrations were historically detected from wells EW-1 and EW-2 (southwest corner of UST tank pmt area)at concentrations as high as 3,300 lig/l. (July 2000) Declining MTBE concentrations were evident from all ten ground water extraction wells during operation of the P&T remediation system, at various stages during P&T operations, MTBE concentrations approached non detectable levels from all ten of the extraction wells (Table 7) • The mass-volume estimate of MTBE-impacted soil remaining at the site were determined by splitting the modeled`elbow'-shaped soil plume into two segments(north segment and south • segment) The volume of each segment was determined by utilizing the formula for an elliptic cone For the northern segment, a semi-mmnor axis of 8 feet, a semi-mayor axis of 57 feet, a Advanced GeoEnviroomental,Inc