ARCHIVED REPORTS XR0000697 - Laserfiche WebLink

Home Browse Search

40 31 August 2005 AGE-NC Protect No 96-0232 Page 18 of 30 utilizing the formula for an elliptic cone (V='/anabh),where `a' represents the semi-mayor axis, `b' represents the semi-minor axis and `h' represents the height of the elliptic cone For the northern segment, a semi-minor axis of 8 feet, a semi-mayor axis of 57 feet, a height of 140 feet and an average MTBE concentration of 0 077 mg/kg were used to estimate the coned elliptical volume of MTBE-impacted soil For the southern segment, a semi-minor axis of 8 feet, a semi-mayor axis of 57 feet, a height of 110 feet and an average MTBE concentration of 0 145 mg/kg were used to estimate the coned elliptical volume of MTBE-impacted soil When the data collected at the site is plotted in both plan view and cross sectional views, the apparent volume of MTBE impacted soil totals approximately 4,433 cubic yards, which yielded a total of approximately 1 54 pounds of MTBE,or an estimated 0 25 gallons of MTBE remaining in soil at the site Volume calculations are included in Appendix L 4.0. ASSESSMENT OF HYDROCARBON-IMPACTED GROUND WATER AGE has interpreted previous investigative results to indicate that a Flag City Chevron unauthorized release of MTBE occurred in the areas of the UST pit and the fuel dispensers The most intense on- site MTBE concentrations were historically detected adjacent the southwest corner of the UST area from wells MW-1 (5,700 µg/1, June 2000), EW-1 (1,800 µg/1, April 2000) and EW-2 (3,300 µg/1, July 2000) AGE previously modeled the Flag City Chevron dissolved plume to have migrated through First Zone and Second Zone ground water, approximately 180 feet westward to the area of the former Rocky's Restaurant domestic water well,at which point the plume appeared to converge with that of a Three B's Truck Plaza MTBE ground water plume Off-site towards the west, the vertical extent of the Flag City Chevron dissolved MTBE plume was modeled to have reached depths as great as 75 feet bsg (MW-1 I B) near the Rocky's Restaurant domestic water well, the maximum westward extent of the Flag City Chevron plume was most likely in the area of the former Rocky's Restaurant domestic drinking water well(RDW-1)due to the previous pumping activity of the domestic water well The estimated extent of First Zone dissolved MTBE between July 1996 and March 2005 is illustrated in Appendix H,Second Zone dissolved MTBE between March 2001 and March 2005 is illustrated in Appendix I After November 2000(pump-and-treat remediation start-up),on-site MTBE concentrations sampled from Flag City Extraction wells EW-1 through EW-10 all generally declined to either non-detect (EW-1, EW-2, EW-3, EW-6, EW-7, EW-10) or near non-detectable levels (EW-4, EW-5, EW-8, EW-9) Furthermore, on-site First Zone ground water monitoring well MW-1 had declined to non- detect MTBE levels by December 2001 and MW-4 had declined to non-detect MTBE levels by March 2001, on-site wells MW-2 and MW-5 were already at non-detectable levels prior to November 2000 On-site Second Zone well MW-8A was already at non-detect levels prior to November 2000 and well MW-9A reached non-detect levels by September 2002 Advanced GeoEnvironmental,Inc