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T 01 December 2004 AGE-NC Project No 97-0333 ' Page 9 of 11 S i ' start-up in January 2002 (Table 5) • Dissolved MTBE was detected from grab samples collected at the influent end of the treatment system at concentrations between 2,200 µg11 and 7,500 µg/1, laboratory analysis ' of grab water samples collected at the effluent end did not detect any constituents of concern during the second quarter 2004 (Table 1) ' Between 10 March 2004 and 23 June 2004, an estimated 12 67 pounds of MTBE was extracted from ground water(Table'5,Appendix C), a total mass of 246 57 pounds of MTBE has been removed since initiation of the pump and treat system on 21 January 2002 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 D, although a slight increase was reported during the first/second quarter 2004 monitoring events, the ' overall general trend of decreasing MTBE,concentrations is evident ' The results from the ground water monitoring and sampling event performed on 22 and 23 June 2004 are as follows ' Generally,depth to ground water at the site varied between 22 and 28 feet bsg, ground water elevations ranged between 4 57 feet (MW-11B & MW-11F) and 9 75 feet (MW-6) above mean sea level The ground water elevation decreased approximately 4 37 feet between the ' March 2004 and the June 2004 ground water monitoring events, the average decrease in elevation may be due to seasonal fluctuation • First Zone ground water flow was inferred to be towards a ground water depression in the ' area of wells EW-1,MW-6 and MW-7A at an approximate of gradient 0 009 ft/ft(Figure 4) • Second Zone,Third Zone and Primary Aquifer ground water flow was inferred to be towards ' the northwest at approximate gradients of 0 001 ft/ft or less(Figures 5,6 and 7,respectively) • 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 samples, collected in the area of First Zone monitoring wells MW-1, MW-2 and MW-3 at concentrations as high as 23,000 pg/l(EPA Method 8260) Lower concentrations of on-site MTBE were detected in water samples from First,Second,Third and Primary Aquifer Zone monitoring wells MW-4,MW-7 (A-E),MW-8 (A and C} and MW-9(A and B) Generally, a moderate to significant MTBE increase was reported at well MW-1,conversely,significant ' decreases were reported from on-site wells MW-2, MW-7 (A and E) and MW-8A(Figures — -8 and 9, Table 3) --- - - - - -- - - -- - - - - - - - - - - ' Advanced GeoEnvironmental,Inc 1 '