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c. An appropriate non -clogging dewatering device will be installed to maintain a 10 -year, <br />24-hour storage volume. <br />d. Appropriate combinations of principal and emergency spillways to safely discharge the <br />runoff from a 25 -year, 24-hour precipitation or larger event, as required by the DRMS's <br />regulations, will be installed. <br />The sediment storage capacity of the sedimentation pond will be periodically monitored to <br />ensure that sediment storage is available beneath the principal spillway inlet (based on the USLE <br />or the equivalent sediment storage of one 10 -year, 24-hour storm event based on the MUSLE). <br />When adequate capacity is no longer available, corrective actions will be taken to restore <br />adequate sediment storage capacity to the pond. Corrective action to restore adequate sediment <br />storage capacity will include removal of accumulated sediment from the pond. <br />The excavated material suitable for topsoil will be salvaged and used for reclamation. The <br />excavated material that is not suitable for a topsoil -like medium will be graded into the <br />surrounding topography within the disturbance area, topsoiled, and revegetated in accordance <br />with New Horizon's approved reclamation plan. Site specific conditions will determine the <br />construction methods and equipment utilized at the time of excavation. Sediment removal and <br />water discharges will be conducted consistent with the approved mining permit and Rule <br />4.05.6(3)(b). All sedimentation ponds will be inspected quarterly under the supervision of a <br />registered professional engineer and reported to the DRMS. <br />Pit dewatering into Pond 007 was primarily a constant occurrence while mining was taking place <br />east of 2700 Road. The dewatering process was operation -controlled, depending on various <br />factors which may include the location of the pit inflows, the location of standing water in the <br />pit, or the location within the pit of the overburden and coal removal operations. When pit <br />dewatering was required, the anticipated dewatering rate was in the range of one to two cubic <br />feet per second or less. Once mining continued west of 2700 Road, Pond 011 was used to detain <br />the pit pumping prior to discharge. At that time, Pond 007 will be somewhat over designed. A <br />new discharge point has been applied for to utilize the Pond 011 site. Actual water flow velocity <br />going into Pond 007 and Pond 011 will be controlled with adequate erosion control (i.e., rock <br />riprap, geotextiles, etc.) or discharged onto non -erodible bedrock material. This will minimize <br />erosion of the pond banks. <br />Updates and modifications to the mine pit dewatering plan are described in Section 2.05.3(3), <br />subsection 6. <br />Pit dewatering will have an insignificant impact on Pond 007, as shown in Attachment 2.05.3(3)- <br />2. Pit dewatering will be sporadic versus continuous. The flow rate of one to two cubic feet per <br />Section 2.05.3(3) Page 5 April 2017 (MR -104) <br />