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F i 5 10 31 October 2005 AGE-NC Project No 03-1080 ' Page 5 of 10 (Bl-GW)at concentrations of 2,100 µg/1,7,200µg/1,7 9µg/l,and 63 µg/l,respectively,in addition, MTBE and 1,2-DCA were detected in sample B1-GW at concentrations of 18 µg/1 and 2 7 µg/1, respectively Figures 5 and 6 depict the estimated vertical extent of petroleum hydrocarbon contamination in soil According to the laboratory report,the petroleum hydrocarbons are remnants of degraded gasoline (Appendix E) 5.0. ESTIMATED MASS OF PETROLEUM HYDROCARBONS r Based on analytical results for soil samples collected at the site to date, AGE calculated that an ' estimated 52 lbs, or 7 8 gallons, of total petroleum hydrocarbons appear -to remain in the predominantly silty sand/silty soil Estimation of the MTBE mass in soil is more uncertain, since MTBE was detected only in soil stockpile SP2A-2B at a concentration of 0 019 mg/kg'Since ' dispenser D1 was the only location where concentrations of petroleum hydrocarbons in soil were sufficiently high to result in a high MTBE reporting limit(<5 0),it can be inferred that dispenser D 1 -` was the source In addition, since MTBE was not detected in soil borings B1 through B3, AGE ' inferred that the extent of MTBE-impacted soil is limited to the immediate area of dispenser D1 (within the 1,000 mg/kg iso-concentration line, Figure 7) AGE calculated that an estimated ' . 0 00005 lbs, or 0 000008 gallons, of MTBE appear to remain in soil The assumptions for the calculation of hydrocarbon mass remaining in soil is presented in Appendix F The volume of petroleum-impacted ground water from the dispenser area could not be accurately i determined based on just the three soil borings(B 1 through B3) Since the concentrations of MTBE amdX1,2-DCA detected in boring B1 were consistent with MTBE and 1,2-DCA concentrations left -'"inplace afterthe original site closure in 1998,and because 1,2-DCA was not detected in soil samplesy'i u at the dispenser location,AGE concludes that the MTBE and 1,2-DCA distribution patterns would be similar to those included in the APEX-prepared Response to Delay No Further Action Required' 4u; y Decision and Closure Request, dated 07 July 1998 (see Appendix B) Since the remaining contaminants (TPH-g, TPH-d, ethylbenzene, and xylenes) in ground water were only detected in boring B 1, AGE concludes that the extent of the remaining contaminants is localized Boring B2, ' adjacent to former well MW-2(not impacted from May 1995 to closure iriNovember 1997),was not impacted Farmer well MW-4, approximately 65 feet northe t ovispenser D1, also was not impacted by TPH-g, TPH-d, ethylbenzene, and/or xylenes from I aa f 995 to closure in November ' 1997 Based on the assumption that the detected fuel represents aged or degraded hydrocarbons that were not detected in ad}acent boring f and monitoring wells,and a dominantly northeasterly ground water flow direction, AGE provides a map depicting the possible lateral extent of TPH=impacted ' ground water(Figure 8) �'o y � sq,Z tr r ' Advanced GeoEnvironmental,Inc 1