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3.2.2 Modeling Results <br />The results of the SEDCAD modeling are provided in Appendix F. Modeling demonstrates that the <br />existing sediment pond is adequate to control and treat runoff from the RPE and the RPEE for the 10 - <br />year, 24-hour storm. The 10 -year, 24-hour and 100 -year, 24-hour storm event flood elevations for the <br />sediment pond are shown on the permit drawings in Appendix D. <br />3.3 Ponds, Impoundments, Other Treatment Facilities and <br />Diversions <br />The sedimentation pond serving the RPE provides adequate capacity to store the runoff from the 10 - <br />year, 24-hour storm event for the combined RPE and RPEE areas. Sediment and clear water <br />diversion ditches have been designed for the RPEE to provide capacity for runoff from the 100 -year, <br />24-hour storm to meet requirements of the Rules. Additional information regarding these facilities is <br />provided in the following sections. <br />3.3.1 Design Inputs and Assumptions <br />The three main design components for surface water runoff control for the RPEE include: <br />• Sediment ditches to capture surface runoff from the RPEE waste rock pile <br />• Clear water diversion ditches to capture and divert surface runoff from areas above the waste <br />rock pile <br />• Sedimentation pond to capture and treat runoff from the sediment ditches <br />3.3.2 Hydrologic and Hydraulic Design Assessment <br />The RPEE sediment and clear water ditches have been designed to safely pass runoff from the 100 - <br />year, 24-hour storm event, as demonstrated by the results of the SEDCAD model provided in <br />Appendix F. The sedimentation pond has capacity to store approximately 5.9 acre-feet of runoff and <br />sediment below the crest of the outlet headwall control elevation of 6106.0 MSL. This provides <br />adequate capacity to store and treat the runoff from the 10 -year, 24-hour storm from both the RPE <br />and the RPEE. Larger storms will overtop the headwall and discharge through the primary outlet <br />18 <br />PAMpls\06 CO\26\06261003 MCC Refuse Pile Site Review & Permit\WorkFiles\Permit Application\2014 Revision\Exhibit 82 2014-05- <br />29.docx <br />