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. 31 August 2005 AGE-NC Project No 96-0232 Page 19 of 30 Based on previous investigation results from soil borings P36 through P38(October 2002),AGE had previously been able to model the area north of the Flag City Chevron property as not being MTBE- impacted However, based on investigation results from soil borings P39 through P43 (January 2004), MTBE was later detected at concentrations of 540 µg11 from Banner Avenue (P43) and 570 µg11 from the McDonald's parking lot(P39) Additionally, previously non-impacted well MW-8A became impacted by MTBE at a concentration of 700 µg/1 in March 2002 Therefore, after March 2002,a third, distinct MTBE ground water plume (New West Petroleum ground water plume)was modeled north-northeast of Flag City Chevron in First Water Zone that extended from at least Banner Avenue (Appendix H) The most intense northward First Zone MTBE concentrations were previously detected on Banner Avenue from well MW-19A (5,300 µg/l, May 2004) and well MW-20A(440µg/1,March 2005) The most intense northward Second Zone MTBE concentrations were previously detected near the northern edge of the Flag City Chevron property from well MW-8A(900 µg/1,March 2003),MW-19B (58 µg/1,May 2004)and MW-20B(4 5 µg11,December 2004) AGE has modeled the New West Petroleum MTBE plume as being influenced by Flag City Chevron P&T operations, and drawn towards the pump-and-treat cone of depression Ground water pump-and-treat operations were fully suspended at the site on 17 August 2004 However, a significant spike of MTBE was recently observed from Flag City Chevron well MW-2 during December 2004, March 2005 and June 2005, and from extraction wells EW-7 and EW-10 during July 2005, AGE has modeled the increases as related to the suspension of the ground water pump-and-treat activities (17 August 2004), in effect causing MTBE-impacted ground water near the Flag City Chevron fuel dispenser area to migrate east-southeast relative to the natural ground water flow direction AGE has modeled the New West Petroleum ground water plume as being drawn toward the Flag City Chevron UST and fuel dispenser area (Figure 17), the new lateral and vertical extent of the dissolved MTBE plume is currently only defined towards the west,southwest and south(Figure 16), and is undefined in all other directions Therefore,volume-mass calculations of the dissolved MTBE plume remaining at the Flag City Chevron can only be estimated based on known ground water data and northward projections Figures 14 and 15 depict the estimated extent of MTBE-impacted ground water in cross sectional views C-C'and E-E', Figures 16 depicts the most current estimated extent of First Zone dissolved MTBE-impacted ground water in plan view Based on Figures 14 through 16, monitoring wells MW-2,MW-4,MW-8,MW-19,MW-20 and extraction wells EW-1 through EW-10 are all located within a dissolved MTBE ground water plume on the north side of Thornton Road (i e Flag City Chevron ground water plume and New West Petroleum ground water plume) Utilizing Figures 14 through 16, the mass-volume distribution of MTBE concentrations remaining on the Flag City Chevron property can be determined by splitting the modeled `elbow'-shaped ground water plume into two segments (western impacted-ground water segment and eastern impacted-ground water Advanced GeoEnvironmental,Inc