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20 <br />(4) Ponds, Impoundments and Diversions <br />The Sediment and Surface Water Control Plans are shown on Maps 13 and 14 for the <br />East Portal and West Portal respectively. The Operator submitted these plans as a <br />technical revision to the permit. These revisions have been necessary because of <br />preparation plant construction; refuse area construction, and the need for more <br />efficient routing of disturbed water as well as ease of maintenance of the overall <br />drainage system. The area north of Ditches D 11, and D 19 to the Highway 12 <br />easement were graded, covered with subsoil and topsoil, mulched and seeded during <br />August and September of 1990. <br />The Operator has three sediment ponds, which collect surface disturbance runoff <br />from the East Portal area. These ponds are 004, 007 and 008. A fourth pond, pond <br />005, was reclaimed in 2003, as the area serviced by this pond was never used for <br />mining related activities. These sedimentation ponds and associated diversion ditches <br />have been designed according to Section 4.05.6 of the DRMS Regulations. In <br />addition, the diversion structures have been designed utilizing the requirements of <br />4.05.3 and 4.05.4. Typical sections of the emergency spillways and embankments of <br />each sediment control structure are shown in Figure 3, Typical Embankment Cross <br />Section. Typical diversion sections are provided on Map 13 Sediment and Surface <br />Water Control Plan- East Portal. Table 20, Ditch Data, is a summary of the diversion <br />(ditch) data relating to Map 13. Table 21, Culvert Sizing and Figure 23, Culvert <br />Sizing Nomograph, provide backup for culvert sizing as per requested drainage <br />modifications. Table 23, Sediment Pond Dimensions, is a summary of sediment pond <br />dimensions. <br />The Operator will control West Portal drainage using ditches, containment areas and <br />bypass culverts. All structures are shown on Map 14, Sediment and Surface Water <br />Control Plan -West Portal. Calculations are found in Exhibit 19, Sediment Design <br />Specifications. <br />Runoff from the DWDA #3 is routed through a series of diversion ditches and will be <br />routed to Containment Area No. 2. The sedimentation control plan for the DWDA <br />#3 is contained in Exhibit 19(22) and was evaluated based on the 100 -year, 24-hour <br />event. Runoff from the undisturbed upland areas to the west are diverted around the <br />pile in ditch D49. Runoff from a small -undisturbed upland area east of the pile is <br />routed through the diversion ditches and routed to containment area 2. <br />Ditches 27 and 69 will direct runoff to Containment Area 2. Containment Area 2 has <br />been designed to contain the 25 -year, 24-hour event, per Rule 4.05.9(2)(e) and as <br />such an emergency spillway system is not required. The total drainage area for <br />Containment Area 2 is 13.14 acres. A total of 1.93 acre-feet of storage is required to <br />handle the 25 -year 24-hour event. The required water storage volume is 1.84 acre- <br />feet, and the three-year sediment volume is 0.1 acre-feet. <br />Ditch 28 will direct a combination of disturbed and undisturbed runoff to <br />Section 2.05 RN -6 10/17/2016 <br />