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15 October 2002 <br /> . AGE-NC Project No 96-0232 <br /> Page 14 of 19 <br /> • A plot of cumulative ground water pump and treat mass removal versus time and a plot of <br /> influent ground water MTBE concentrations versus time suggest a continued trend of <br /> decreasing MTBE concentrations (Appendix E) <br /> The results from the ground water monitoring and sampling events performed in September 2002 <br /> gr g p <br />' are as follows <br /> • Generally,depth to ground water at the site vaned between 17 and 20 feet bsg, ground water <br /> elevations range between 7 34 feet (MW-10E) and 11 07 feet (MW-13B) below mean sea <br />' level <br /> • First Zone ground water flow appeared to be directed towards the northwest near the Flag <br />' City Chevron site at an approximate gradient of 0 005 ft/ft, and directed towards the <br /> southwest near the Rocky's Restaurant and Three B's Truck Plaza sites at an approximate <br /> gradient of 0 006 ft/ft (Figure 4) <br />' • Second Zone ground water flow appeared to be directed towards the southwest near the Flag <br /> City Chevron site at an approximate gradient of 0 002 ft/ft, and directed towards the west- <br /> southwest near the Rocky's Restaurant and Three B's Truck Plaza sites at an approximate <br /> gradient of 0 006 ft/ft (Figure 5) <br /> • Secondary Aquifer Zone ground water flow appeared to be directed towards the west- <br /> northwest near the Flag City Chevron site at an approximate gradient of 0 004 ft/ft, and <br /> directed towards the west-southwest near the Rocky's Restaurant and Three B's Truck Plaza <br /> sites at an approximate gradient of 0 006 ft/ft (Figure 6) <br />' • Primary Aquifer Zone ground water flow appeared to be directed towards the west-northwest <br /> near the Flag City Chevron, the Rocky's Restaurant and the Three B's Truck Plaza sites at <br />' approximate gradients of less than 0 002 ft/ft (Figure 7) <br /> • Due to the low ground water gradient at the site, small variations in ground water <br /> measurements or changes of recharge/discharge of the local ground water could greatly <br /> modify the inferred ground water flow direction <br /> • The average decrease of ground water elevation of approximately 6 36 feet between June <br />' 2002 and September 2002 may be due to seasonal fluctuation Hydrographs depicting <br /> recorded groundwater elevations at wells MW-2,MW-6A and MW-6B vs time are provided <br /> in Appendix I <br />' • The highest on-site concentrations of dissolved MTBE were detected in the sample collected <br /> from First Zone extraction well EW-9 at 43 µg/l,lower concentrations of on-site MTBE were <br /> detected in water samples from First Zone extraction wells EW-1, EW-2, EW-4 through <br /> EW-8 and EW-10, and from Second Zone monitoring well MW-8A (Table 6), decreasing <br /> i <br /> Advanced GeoEnvironmental,We <br />