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31 March 2006 <br /> AGE-NC Project No. 98-0471 <br /> Page 8 of 13 <br /> • An estimated 3.3 lbs, or 0.4 gallons, of toluene remain in soil; <br /> • An estimated 1.2 lbs, or 0.2 gallons, of ethylbenzene remain in soil; and <br /> • An estimated 7.4 lbs, or 1.0 gallons, of xylenes remain in soil. <br /> All calculations,including maps of the estimated lateral distribution of contaminants in soil,for the <br /> mass of adsorbed TPH-g, TPH-d, TPH-mo, MTBE, and BTEX are included in Appendices B <br /> through I, respectively. <br /> 7.0. PETROLEUM HYDROCARBON IMPACT TO GROUNDWATER <br /> Historically,petroleum hydrocarbon-impacted ground water has been detected consistently only in <br /> monitoring wells MW-1 and MW-3, with occasional detections in wells MW-2 and MW-4. <br /> Monitoring wells MW-5 and MW-6 have remained uncontaminated and,with the exception of the <br /> initial ground water sample after well installation,petroleum hydrocarbons have not been detected <br /> in well MW-7 (Table 3). During the last ground water monitoring event, conducted in the second <br /> quarter 2005, TPH-g and MTBE were detected in well MW-3 at equivalent concentrations of <br /> 100 µg/1;the detection of TPH-g is most likely due to the MTBE component. The estimated lateral <br /> distribution of dissolved MTBE is illustrated on Figure 7. <br /> Based on assumptions of average concentrations of analytical results for ground water samples <br /> collected from monitoring wells MW-1 and MW-3 on 06 May 2005 (second quarter 2005), AGE <br /> calculated of the mass of MTBE remaining in ground water to be approximately 0.014 lbs, or <br /> 0.002 gallons. <br /> Calculations for the mass of dissolved MTBE are included in Appendix L. <br /> 7.1. PETROLEUM HYDROCARBON CONCENTRATION TRENDS <br /> Historically, ground water monitoring well MW-1 has been the most impacted well at the site; <br /> laboratory analysis has reported TPH-g, TPH-d, MTBE, and BTEX compounds at concentrations <br /> as high as 4,300 µg/1 TPH-g, 350 µg/1 MTBE, 95 µg/1 benzene, 220 µg/1 toluene, 170 µg/1 <br /> ethylbenzene, and 500 µg/1 xylenes during the initial ground water monitoring event in June 2000, <br /> and 1,400 µg/1 TPH-d in October 2000 (Table 3). The concentrations of petroleum hydrocarbon <br /> contaminants in well MW-1 have steadily declined between the initiation of ground water <br /> monitoring to the present;since June 2000,the concentrations of TPH-g,TPH-d,MTBE,and BTEX <br /> have decreased below detection limits. <br /> Advanced Geo Environmental,Inc <br />