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30 October 2004 AGE-NC Project No 96-0232 Page 11 of 14 • Generally,depth to ground water at the site vaned between 15 and 18 feet bsg,ground water elevations ranged between 3 73 feet (MW-13D) and 4 76 feet (MW-lOE) below mean sea level (Table 2) _ • Net ground water flow direction in all informal hydrogeologic units was Inferred to be east- southeast at the Flag City Chevron site and east-northeast at the Three B's Truck Plaza, hydraulic gradients were calculated to be 0 002 ft/fl or less Due to the low ground water gradient at the site, small variations in ground water measurements or changes of recharge/discharge of the local ground water could greatly modify the inferred ground water flow direction • The highest on-site concentrations of dissolved MTBE were detected in the sample collected from Second Zone well MW-8A at 220 µg/l (Figure 9), lower concentrations of on-site MTBE were detected in water samples collected from First Zone wells MW-5, and from Second Zone monitoring well MW-9A, a significant MTBE decrease was reported at well MW-8A • The most intense First Zone off-site MTBE-impacted ground water were detected from the area of Flag City Chevron wells MW-16 and MW-19A at concentrations as high as 1,300 ® µg/1 and Three B's Truck Plaza wells MW-1, MW-2, MW-4, MW-5 and MW-8A at concentrations as high as 110 gg/l(Figure 8) The most intense Second Zone off-site MTBE- impacted ground water were detected from the area of Flag City Chevron wells MW-17 and MW-19B at concentrations as high as 40 gg/1 (Figure 9) Between the March 2004 and September 2004 quarterly monitoring events, a significant MTBE decrease was reported at well MW-17, from 140 ggll to 87 µg/1 to 40 µg/l • The most intense Rocky's Upper Zone off-site MTBE impacted ground water were detected from the area of Flag City Chevron wells MW-11B and MW-18 at concentrations as high as 130 µg/1 (Figure 10, Table 4) • Low concentrations of TPH-d have been detected at various wells during previous quarterly monitoring events at Flag City Chevron During September 2004, a low concentration of TPH-d was detected in the water samples collected from well MW-12A AGE had previously asked McCampbell Analytical Laboratory to review the TPH-d sample chromatograms from MW-12A, the laboratory concluded that the low TPH-d detections from MW-12A did not have typical diesel characteristics,and that the detected chromatogram peaks were probably the result of biological interference Advanced GeoEnvironmental,Inc