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CLEAOR2W'IAOTER <br /> G R U U P, I N C. <br /> carbon dioxide generation in the formerly contaminated zone will closely <br /> approximate these processes in areas that had no contamination. It is <br /> therefore important to measure "background" concentrations and to <br /> periodically measure the concentrations in soil vapor samples for purposes of <br /> comparison. <br /> Furthermore, the less volatile fraction of hydrocarbons may remain adsorbed <br /> to soil even though the hydrocarbon concentrations measured in exhaust <br /> vapors suggest that the soil has been adequately remediated. Analyses of soil <br /> samples from confirmation borings could indicate that cleanup levels have <br /> not been attained, necessitating system re-start and the drilling of additional <br /> confirmation borings. Use of biogenic gas data may aid in evaluating the <br /> appropriate time at which to discontinue SVE operations. We appreciate <br /> your reconsideration of our proposal to begin collecting biogenic gas data at <br /> the subject location. <br /> We hope that your concerns have been addressed. In summary, Clearwater <br /> would like to proceed with the following actions at the subject site: <br /> - Operate the SVE system with wells VW-1, VW-2, and VW-3 on-line for <br /> approximately one week; collect data regarding flow rates, vacuum, and <br /> vapor concentrations <br /> - Continue operation of the system as described above with VW-4 and VW-5 <br /> only on-line <br /> - Complete respiration test as previously described <br /> - Submit a revised spreadsheet and calculation details to the PHS/EHD, after <br /> receiving your input. <br /> Regards, <br /> Clearwater Grou , Inc. <br /> eanna S. Hudson, R.G. <br /> Project Manager <br />