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Designs for all Ditches in the Permit Area <br />Steps taken in the ditch designs are outlined in the Arcadis report in Appendix 2.05.3(4)- <br />1. <br />Sedimentation Ponds <br />Sediment pond design details are discussed in the Arcadis report (Appendix 2.05.3(4)- <br />1). In accordance with 4.05.2 and the approved Water Discharge Permit from Colorado <br />Water Quality Control Division, WFC will use Ponds NHN -001, NHN -002 and NHN -003 <br />to 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 Arcadis report for <br />design calculations. <br />A 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 <br />Federal regulations for all effluent limitations before discharge from the <br />permit area. The characteristics of the mine site, reclamation procedures, <br />and on site 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 <br />safely discharge the runoff from a 25 -year, 24 -hour precipitation or larger <br />event, as required by the DRMS' regulations. <br />The sediment storage capacity of the sedimentation ponds will be periodically monitored <br />to ensure that at least one year 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 <br />the following: <br />Raise the spillway and redesign the pond in order to restore adequate <br />storage 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 November 2011 <br />