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t30 October 2003 . AGE-NC Project No 96-0232 Page 12 of 15 • Laboratory analysis of the 25 July 2003 effluent-end water samples detected MTBE at a ' concentration of 0 71 µg/l (Table 1) The pump-treat effluent was re-sampled on 11 August and on 29 August 2003 and did not detect any MTBE • Between 25 June 2003 and 15 September 2003, the mass of MTBE removed from the extracted ground water was calculated to be 0 13 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 t ' The results from the ground water monitoring and sampling events performed in September 2003 are as follows ' • Generally, depth to ground water at the site vaned between 13 and 17 feet bsg,ground water elevations ranged between 4 90 feet(MW-13B)and 5 68 feet(MW-2)below MSL(Table 4) ' • First Zone ground water was inferred to be radially inward towards a ground water depression in the area of Flag City Chevron wells MW-1, MW-2 and MW-4 at hydraulic gradients of 0 005 ft/ft or less Second Zone and Secondary Aquifer Zone ground water was inferred to flow radially-inward in the areas of Flag City Chevron wells MW-6B and MW-9B, respectively, net ground water flow was towards the south at hydraulic gradients of 0 002 ft/ft or less Primary Aquifer Zone ground water was inferred to be towards the east- southeast at hydraulic gradients of 0 001 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 ' G The average decrease in ground water elevation of approximately 0 69 feet between June 2003 and September 2003 may be due to seasonal fluctuation Hydrographs depicting ' recorded groundwater elevations at wells MW-2,MW-6A and MW-6B vs time are provided in Appendix I The highest on-site concentrations of dissolved MTBE were detected in the sample collected ' from First Zone extraction wells EW-5 and EW-8 at 24 µg/1 (Figure 8) and from Second Zone well MW-8A at 420 µg/l (Figure 9), lower concentrations of on-site MTBE were detected in water samples from First Zone wells MW-4, EW-2, EW-4, EW-6, EW-7 and EW-9, and from Second Zone monitoring well MW-9A,generally, low to moderate MTBE decreases were reported at on-site wells MW-6B, EW-1, EW-4, MW-8A, MW-9A, EW-4, EW-5, EW-7 and EW-10, conversely, low MTBE increases were reported at wells EW-6, EW-8 and EW-9 • The most intense First Zone off-site MTBE-impacted ground water were detected from the in the area of well Flag City Chevron well MW-16 and Three B's Truck Plaza wells MW-4 and MW-8A at concentrations as high as 110 ug/1 (Figure 8) Advanced GcoEnvironmental,Inc