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4. Designs for all Ditches in the Permit Area <br />Steps taken in the ditch designs are outlined in Appendix 2.05.3(4) -1, Appendix 2.05.3(4)- <br />213, and Appendix 2.05.3(4) -8. Designs presented in Appendix 2.05.3(4) -8 for NHN -002 <br />North and South Ditches supersedes designs presented in Appendix 2.05.3(4) -1. <br />5. Sedimentation Ponds <br />Sediment pond design details are discussed in the Arcadis report (Appendix 2.05.3(4) -1) <br />as well as Appendix 2.05.3(4) -8 for Pond NHN -002. Designs presented in Appendix <br />2.05.3(4) -8 supersede all Pond NHN -002 designs presented in Appendix 2.05.3(4) -1. In <br />accordance with 4.05.2 and the approved Water Discharge Permit from Colorado Water <br />Quality Control Division, WFC will use Ponds NHN -001, NHN -002 and NHN -003 to <br />prevent, to the extent possible, additional contributions of sediment to stream flow or <br />runoff outside the permit area due to mining disturbance. Please see Appendix 2.05.3(4)- <br />1 and Appendix 2.05.3(4) -8 for design calculations. In accordance with Rule 4.05.6(3) <br />each sedimentation pond is designed, constructed, and maintained to: <br />a. Provide storage for the runoff or inflow entering the pond as a result of a 10- <br />year, 24 -hour precipitation event and to meet all applicable State and Federal <br />regulations for all effluent limitations before discharge from the permit area. <br />The characteristics of the mine site, reclamation procedures, and on site <br />sediment control practices are also considered in the design. <br />b. Provide adequate sediment storage volume in compliance with the DRMS <br />regulations. <br />c. Install an appropriate non - clogging dewatering device to maintain a 10 -year, <br />24 -hour storage volume. <br />d. Install appropriate combinations of principal and emergency spillways to safely <br />discharge the runoff from a 25 -year, 24 -hour precipitation or larger event, as <br />required by the DRMS' regulations. <br />The sediment storage capacity of the sedimentation ponds will be periodically monitored <br />to ensure that at least three years of sediment storage is available beneath the principal <br />spillway inlet (based on the sediment storage volume calculated using the M.U.S.L.E. <br />contained within the SEDCAD4 program). When adequate capacity is no longer <br />available, sediment removal or other corrective actions will be taken to restore adequate <br />sediment storage capacity to the pond. <br />Corrective action required to restore adequate sediment storage capacity may include the <br />following: <br />Raise the spillway and redesign the pond in order to restore adequate storage <br />capacity and to comply with the applicable regulations. <br />2. Excavate the pond area and enlarge the sediment storage capacity. <br />Section 2.05.3(4) Page 4 September 2014 (TR -06) <br />