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31 March 2006 <br /> AGE-NC Project No. 98-0471 <br /> Page 11 of 13 <br /> detectable levels (<1.0 µg/1) in 2 years (Table 10; Appendix N-2). <br /> RISC model calculations utilizing the Saturated Soil To Ground Water input parameters predicts that <br /> BTEX or MTBE will not be detected in ground water (at approximately 10-10 µg/1) at the down- <br /> gradient well (Appendix N-3). <br /> 8.1.2. Dissolved Source Ground Water Model <br /> Since ground water in the vicinity of the former AST may be impacted by MTBE,fate and transport <br /> analysis was conducted for a Dissolved Source Ground Water model to determine the effect of the <br /> MTBE-impacted ground water plume on any shallow down-gradient well located 130 feet from the <br /> source area. The mean MTBE concentration of 59 µg/1 for the ground water model was determined <br /> utilizing concentrations detected in well MW-3 during the last four quarterly monitoring events in <br /> which well MW-3 was sampled. Input parameters and output calculations and results are presented <br /> in Appendices O and 0-1, respectively. <br /> RISC model calculations utilizing the Dissolved Source Ground Water input parameters predicts that <br /> MTBE will not be detected in ground water (at <10-13 µg/1 range) at the down-gradient well <br /> (Appendix 0-2). <br /> 9.0. SUMMARY AND CONCLUSIONS <br /> Based upon a review of site assessment activities to date, AGE concludes: <br /> • A sensitive receptor survey identified two water wells located within a 2,000-foot radius of <br /> the site; one domestic well, screened from 55 feet to 75 feet bsg, is located on-site <br /> approximately 130 feet northwest(up-gradient)from monitoring well MW-3;one domestic <br /> well, screened from 80 feet to 90 feet bsg, is located approximately 1,340 feet west- <br /> southwest of the site near the west end of the Middle River Bridge. <br /> • The lateral extent of contaminated soil and ground water is defined to the south by well <br /> MW-7, to the east by well MW-2, to the north by well MW-5, and to the west by well <br /> MW-4. <br /> • Historically,petroleum hydrocarbon-impacted ground water has been detected consistently <br /> only in monitoring wells MW-1 and MW-3,with occasional detections in wells MW-2 and <br /> MW-4. Monitoring wells MW-5 and MW-6 have remained uncontaminated; with the <br /> exception of the initial ground water sample after well installation,petroleum hydrocarbons <br /> have not been detected in well MW-7. Natural attenuation is reducing the concentration of <br /> Advanced Geo Environmental,Inc <br />