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08 September 2009 AGE -NC Project No. 03-1055 Page 12 of 19 Figures 7, 8 and 9; the estimated lateral distribution of adsorbed TPH-g concentrations in shallow and deep soil are depicted in plan view in Figures 10 and 11, respectively. 3.2. MASS OF ADSORBED PETROLEUM HYDROCARBONS REMAINING Based on the estimated lateral and vertical extent of residual adsorbed TPH-g which currently impacts soil and a review of analytical results (Figures 7 through 10; Table 1), AGE estimates approximately 104 pounds, equivalent to 17 gallons, of TPH-g remain present at the site. Mass and Volume calculations are presented in Appendix J. 4.0. ASSESSMENT OF HYDROCARBON -IMPACTED GROUND WATER In addition to the 16 soil borings advanced on-site and off-site for the collection of grab ground water samples, between December 2000 and July 2009, AGE performed 24 ground water monitoring events/sampling events at the site to investigate the extent of hydrocarbon -impacted ground water. %4W In May 2000, five soil borings, B 1 through B5, were advanced at the site for the collection of grab ground water samples. TPH-g and one or more BTEX compounds were reported in every sample at maximum concentrations of 55,000 µg11 TPH-g (B3 -H2O), 160 µg11 benzene (B3 -H20), 25 11g/1 toluene (B3 -H20), and 230 µg/l xylenes (B2 -H20). The highest concentrations of contaminants appeared to be in the region of B3, in the former northernmost dispenser area. In July 2003, four soil borings, B6 through B9, were advanced off-site, for the collection of grab ground water samples, along the western boundary of the property (B6 through B8) and along the eastern boundary of the former Chevron (B9) on Adams Street. TPH-g and one or more BTEX compounds were reported in every sample at maximum concentrations of 800,000 µg11 TPH-g (B6-12), 80 µg11 benzene (B9-13), 16 µg/l toluene (B9-13), 3,100 µg%1 ethylbenzene (B6-12), and 1,800 µg11 xylenes (B6-12). Benzene was only reported in the off-site boring B9. MTBE was reported in three samples at a maximum concentration of 28 µg/( in borings B6 and B9. Prior to this investigation, MTBE had not been reported in any ground water sample --all previous investigations were conducted on-site. The highest concentrations of contaminants appeared to be in the area of B6, southwest of the yet to be discovered 500 -gallon UST encountered in October 2003 during soil excavation activities. In September 2007, six off-site soil borings were advanced for the collection of grab ground water samples; borings B 12 through B 15 were located near the center of Adams Street, and borings B 10 and Bl 1 were located east of the former Chevron site on the sidewalk. TPH-g were reported in all samples at concentrations ranging between 200 µg/l (B 10-12) and 9,700 µg/l (B 15-12). One or more Advanced GeoEnvironmental, IRC.