ARCHIVED REPORTS_XR0006871 - Laserfiche WebLink

Home Browse Search

1 , 1 OS January 2004 AGE-NC Project No 97-0333 Page 9 of 11 • Approximately 93,812 gallons of hydrocarbon-impacted ground water were extracted from ' well EW-1,which was completed in the First Zone aquifer A total volume of approximately 2,550,212 gallons of hydrocarbon-impacted ground water has been treated at the site since ' start-up in January 2002 (Table 1) • Dissolved MTBE was detected from grab samples collected at the influent end of the treatment system'at concentrations between 3,400 µg/1 and 6,600 µg/1, laboratory analysis of grab water samples collected at the effluent end did not detect any constituents of concern during the third quarter 2004 (Table 2) ' Between 23 June 2004 and 15 September 2004, an estimated 4 43 pounds of MTBE were extracted from ground water(Table 1, Appendix Q, a total mass of 251-pounds of MTBE have 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 slight MTBE-increases was reported at the influent during the June/September 2004 monthly monitoring events,the overall general trend of decreasing MTBE concentrations is evident , . The results from the ground water monitoring and sampling event performed on 04 and 05 October 2004 are as follows ' • Generally,depth to ground water at the site varied between 24 and 28 feet bsg,ground water elevations ranged between 4 75 feet (MW-IOD) and 7 03 feet (MW-3 and MW-5) above MSL The ground water elevation decreased approximately 0 52 feet between the June 2004 and the October 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-4 MW-6 and MW-7A and north-northeast off-site, at an approximate of gradient 0 001 ft/ft(Figure 4) • Second Zone,Third Zone and Primary Aquifer ground water flow was inferred to be towards ' the north-northeast 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-2 and MW-3 at concentrations as high as 17,000 µg/l Lower concentrations of on-site MTBE were detected in water samples from First,Second,Third and Primary Aquifer Zone monitoring wells MW-1,MW-4,MW-7 ' Advanced GeoEnvironmental,inc