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Technical Revision No. 79 -PAR Responses 10 April 18, 1997 Page used at the Lower Refuse Pile. Based on the above empirical observations from the revegetation at the Lower Refuse Pile, it is logical to extrapolate the same success to revegetation at the RPE. Miti¢ation of the Imaacts of MininE Operations 41. The approval granted by the Army Corps of Engineers for the disturbance to the wetland in the RPE azea and the mitigation site is included in Appendix C, submitted with the original application. Also enclosed for the Division's files are the mitigation construction plans for the wetland site. 42. The probable hydrologic consequences associated with the RPE will be included in the separate PHC revision which will be submitted to the Division in the near future. 43. MCC intends to fully comply with the NPDES permit issued for this discharge point by the Colorado Department of Public Health and the Environment. MCC will also continue to monitor quality and quantity of the North Fork of the Gunnison River. 44. Please refer to responses provided in questions 2, 27 and 28. 45. The SAE demonstration for the North Soil Storage Area involved computing the 10-year, 24-hour Type II storm surface runoff and the anticipated soil loss. Storm runoffwas computed using the SCS runoff curve number method with a CN of 88 for the entire site. The soil loss was derived using the Universal Soil Loss Equation. A control practice factor of 0.1 was used under the assumption that the stockpiles would be seeded for revelation. A silt fence installed half-way down the face of each stockpile is also assumed. The total computed soil loss fora 10-year, 24-hour storm is computed to be 0.007 acre-feet, the total surface runoffis estimated to be 0.28 acre-feet. Because this exceeds the 0.5 mUl peak settleable concentration of sediment, a small 0.5 acre-feet sediment pond has been added to the North soil Storage Area. The pond will contain the 10-year, 24-hour storm runoff, plus has 0.22 acre-feet additional capacity for sediment which is estimated to accrue at an annual rate of 0.01 acre-feet per yeaz. All new ditches required to route the runoff into the sediment pond aze designed to carry the 100- yeaz, 24-hour storm runoff peak flow with 0.5 feet of freeboard. The emergency spillway is also designed to carry the 100-yeaz, 24-hour storm runoff peak flow and is lined with 6-inch diameter rip rap. Ditch and pond calculations are enclosed and should be incorporated into Exhibit 66. Figure 2.0 has been revised to show the location of the sedimentation pond and should also be incorporated into Exhibit 66.