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<br />area were not changed. Estimated pit depths corresponding to each specific setback area <br />can be referenced in the slope stability analysis included in Attac}unent R of the May 24, <br />2000 applicant response letter. <br />The applicant may perform additional slope stability analyses in the future that address <br />the Division's concerns. If the results indicate that the setbacks can be decreased, the <br />applicant will submit the analyses and any new proposed setbacks as a technical revision <br />to the proposed permit. <br />13. Page 8 of the May 24, 2000 response states "It was assumed that 9 percent of the dewatering <br />flow contained non-DIMP constituent concentrations." Please explain how the 9 percent figure <br />was determined. <br />• The 9 percent area corresponds to the percentage of the pit dewatering drawdown area <br />covered by the 1999 delineated area of DIMP located south-southwest of the proposed <br />Tanabe site (see Figure in Attachment N of the May 24, 2000 applicant response letter). <br />Concentrations of non-DIMP constituents were detected in samples from isolated wells <br />near the proposed Tanabe site. It was not possible to estimate contaminant "plumes" of <br />each non-DIMP constituent from these isolated well detections. Therefore, the quantity <br />of ground water within the pit dewatering drawdown area containing non-DIMP <br />constituent concentrations could not be calculated. It did appear, however, that the <br />primary detections of non-DIMP constituents were from wells south-southwest of the <br />proposed project site (see Attachment L of May 24, 2000 applicant response letter). This <br />area corresponds to an isolated area south-southwest of the proposed site where 1999 <br />DIMP concentrations were delineated. The isolated area of ground water containing <br />concentrations of DIMP was estimated to cover approximately 9 percent of the pi[ <br />dewatering drawdown area. As a worst-case scenario, it was assumed that the non-DIMP <br />constituents detected near the proposed Tanabe site covered this same area. Based upon <br />the location of the isolated non-DIMP constituent detections, and the non-DIMP <br />constituent average concentrations used in the analysis (see Table in Attachment N of the <br />May 24, 2000 applicant response letter), the estimated concentrations of these <br />constituents drawn into pit dewatering flows are considered to be conservative. <br />The isolated area of DIMP south-southwest of the proposed site, together with the <br />delineated plume to the northeast of the proposed project site, comprised approximately <br />20 percent of the pit dewatering drawdown area as discussed in the May 24, 2000 <br />response to Comment 23. <br />Page 4 <br />