2017-05-12_PERMIT FILE - C2010089A (4)

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NHN-002 designs presented in Appendix 2.05.3(4)-1. In accordance with Rule 4.05.2, NHN will use Ponds NHN-001, NHN-002 and NHN-003 to prevent, to the extent possible, additional contributions of sediment to stream flow or runoff outside the permit area due to mining disturbance. Please see Appendix 2.05.3(4)-1 and Appendix 2.05.3(4)-8 for design calculations. In accordance with Rule 4.05.6(3) each sedimentation pond is designed, constructed, and maintained to: a) Provide storage for the runoff or inflow entering the pond as a result of a 10 -year, 24- hour precipitation event and to meet all applicable State and Federal regulations for all effluent limitations before discharge from the permit area. The characteristics of the mine site, reclamation procedures, and on site sediment control practices are also considered in the design. b) Provide adequate sediment storage volume in compliance with the DRMS regulations. c) Install an appropriate non -clogging dewatering device to maintain a 10 -year, 24-hour storage volume. d) Install appropriate combinations of principal and emergency spillways to safely discharge the runoff from a 25 -year, 24-hour precipitation or larger event, as required by the DRMS' regulations. In accordance with Rule 4.05.9(9), the faces of all embankments and surrounding areas will be vegetated to protect against erosion. Where water will be impounded, the upstream faces of all embankments will also be vegetated to protect against erosion from water or sudden drawdown. Vegetation will occur in accordance with one of the approved temporary seed mixtures. The sediment storage capacity of the sedimentation ponds will be periodically monitored to ensure that sediment storage is available beneath the principal spillway inlet (based on the sediment storage volume calculated using the M.U.S.L.E. contained within the SEDCAD4 program). When adequate capacity is no longer available, corrective actions will be taken to restore adequate sediment storage capacity to the pond. Corrective action to restore adequate sediment storage capacity will include removal of accumulated sediment from the pond. The excavated material suitable for topsoil will be salvaged in a stockpile used for reclamation. The excavated material that is not suitable for a topsoil -like medium will be graded into the surrounding topography within the disturbance area, topsoiled, and revegetated in accordance with the NHN Mine's approved reclamation plan. All sedimentation ponds will be inspected quarterly under the supervision of a registered professional engineer and reported to the DRMS. The pit dewatering process will be a sporadic, operation -controlled occurrence depending on various factors which may include the location of the pit inflows, the location of standing water in the pit, or the location within the pit of the overburden and coal removal operations. When pit Section 2.05.3(4) Page 3 April 2016 (PR -01)