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i I • 31 January 2003 ' AGE-NC Project No 96-0232 + ' ' Page 13 of 17 f 7,469,160 pounds Multiplying the average MTBE concentration(11 µg/1)by the pounds of ' MTBE-extracted water yielded a mass of approximately 0 08 pounds of MTBE removed from the extracted ground water (Table 8, Appendix D) ' • Between 21 November and 05 December 2002, the mass of MTBE-impacted ground water ` processed during operation of the pump and tr6at system was calculated to be 2,283,754 pounds Multiplying the average MTBE concentration (17 µg/l) by the pounds of MTBE- ' extracted water yielded a mass of approximately 0 04 pounds of MTBE removed from extracted ground water (Table 8, Appendix D) r ' • 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, although a slight increase was reported in December 2002, a general trend of decreasing ' MTBE concentrations is still evident • Between 25 September and 29 October 2002, ground water pump-and-treat was suspended due to a detection of hexavalent chromium in the effluent grab water sample, at a ' concentration of 0 30 µg/1 Effluent from the pump-and-treat system was re-sampled on 25 September 2002, the subsequent laboratory analysis reported non-detectable levels of hexavalent chr6mium(less than 0 5 µ,g/1) With the concurrence of the RWQCB,the pump- and-treat system was restarted on 29 October 2002 following The results from the ground water monitoring and sampling events performed in December 2002 are as follows ' • Generally, depth to groundwater at the site vaned between 12 and 16 feet bsg, groundwater elevations range between 3'8_4 feet(MW-13A)and 4 58 feet(MW-9C)below mean sea level ' • First Zone ground water was inferred to flow towards the east-southeast near the Rocky S, Restaurant and Three B's Truck Plaza sites,at an approximate gradient of 0 001 ft/ft or less, towards a groundwater depression in the area ofFlag City Chevron wells MW-1 and MW-2 (Figure 4) • Second Zone ground water was inferred to flow,in a radially inward pattern at the Flag City Chevron site,with a net southerly flow at an approximate gradient of 0 001 ft/ft or less,west of the site, ground water flowed easterly at an approximate gradient "of 0 001 ft/ft or f less(Figure 5)' The Secondary'Aquifer Zone and Primary Aquifer,Zone flow patterns are ' similar to the Second Zone flow pattern(Figures 6 and 7) " • 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 ' Advanced GeoEnvironmental,Inc '