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30 July 2004 AGE-NC Project No 96-0232 Page 12 of 16 • The pump-and-treat remediation system was non-operational between 22 April 2004 and 28 April 2004 due to a mechanical malfunction with the in-line process pump The process pump was repaued/replaced on 28 April 2004 and the pump-and-treat remediation system was re-started • Steady,but low MTBE concentrations were detected from monthly water samples collected at the influent end of the treatment system at concentrations of 16 gg/l, 19 pg/1 and 15 gg/l • Laboratory analysis of pump-treat effluent samples and did not detect any MTBE during the second quarter 2004 • Between 16 March 2004 and 15 June 2004,the mass of MTBE removed from the extracted ground water was calculated to be 0 18 pounds(Table 8,Appendix D) A plot of cumulative ground water pump and treat mass removal versus time and a plot of influent ground water MTBE concentrations versus time are included in Appendix E The results from the ground water monitoring and sampling events performed in June 2004 are as follows . • Generally,depth to ground water at the site vaned between 12 and 16 feet bsg,ground water elevations ranged between 15 8 feet (MW-13B) above mean sea level (MSL) and 2 85 feet (MW-10E) below MSL (Table 4) • Net ground water flow direction in all informal hydrogeologlc units was inferred to be east- southeast at the Flag City Chevron site and east-northeast the Three B's Truck Plaza, hydraulic gradients were calculated to be 0 002 ft/ft 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 First Zone well EW-7 at 79 gg/1(Figure 8)and from Second Zone well MW-8A at 570 µg/1 (Figure 9), lower concentrations of on-site MTBE were detected in water samples collected from First Zone wells EW-4,EW-5,EW-8 through EW-10,and from Second Zone monitoring well MW-9A, a significant MTBE decrease was reported at wells EW-7 and EW-8,whale moderate MTBE increases were reported at wells MW-8A,EW-9 and EW-10 • 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 4,800 pg/l and Three B's Truck Plaza wells MW-I, MW-2,MW-4 and MW-8A at concentrations as high as 130 µg/1 (Figure 8) Advanced GeoEnvironmental,rue