2008-12-04_PERMIT FILE - C1994082A (4)

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FeGruary 1999 Yaart tbline * 13-12 Drainage and Sediment Control Plan •7 4.0 PONDS This attachment covers pond designs for Sedimentation Ponds 011A, 012, 012A, 013 and 014. All ponds are designed to treat the runoff and associated sediment from the 10-year, 24-hour storm event in accordance with Rule 4.05.6 of the Regulations of the Colorado Mined Land Reclamation Board for Coal Mining. The ponds were designed utilizing the SEDCAD4 computer model. The input parameters and results are presented in the SEDCAD4 printouts located in Appendi_Y 13-12.1, Sediment Pond Design SEDCAD4 Results, and summarized in Table 13-12.5, Yoast Mine Sedimentation Pond Design Summary. The locations of Ponds 012, 013 and 014 and the corresponding watersheds used in each respective design are shown on Exhibit 13-12.1, Yoart Mine Watershed. A conservative approach was taken in identifying disturbed and undisturbed areas contributing runoff to each pond. All areas which could possibly be disturbed during the life of the project were identified as either pit/pre-strip or spoil, with curve numbers of 91 and 86, respectively. Areas of concurrent reclamation or in-pit containment of runoff were not taken into account. Please note that these designs and the corresponding watersheds shown on Exhibit 13-12.1 are obsolete. However, the designs and corresponding documentation have been left in the permit application package in accordance with Rule 2.05.3(4). Pond and embankment configurations for Ponds 012, 013 and 014 can be found on Exhibit 13-12.2, Proposed Pond 012 Design, Exhibit 13-12.3, Proposed Pond 013 Design, and Exhibit 13-12.4, Proposed Pond 014 Design, respectively. Pond 012A is an alternative structure that will be used to assist Pond 012 to treat the runoff and sediment from the Pond 012 watershed. Pond O12A was approved by the Division as part of TR-36. A two- pond system design for Ponds 012A and 012 was prepared as part of TR-37. This design incorporates the existing, and approved, Pond 012A design (TR-36) and the existing, and approved Pond 012 as-built (RN-02). The location of Pond 01?A is shown on Exhibit 12-1, Operations Plan; the contributing. watershed is shown on Exhibit 13-12.1A, Permanent Channel and Pond Watersheds. Runoff and sedimentation calculations were based on June 2007 landscape and vegetation conditions. As presented in the Yoast Mine 2006 Annual Reclamation Report (see 2006 Annual Reclamation Chronological Seeding Map), all coal removal activities have ceased and most mining related disturbance areas were reclaimed (98 percent) and successfully revegetated (85 percent) as of spring 2007. The pond and embankment layout for Pond 012A are presented on Exhibit 13-12.7, Pond 012A Design. All ponds have principal and emergency spillways. The principal spillway for ponds 012A, 013 and 014 consists of a 5 foot tall, CMP riser, with an accompanying CMP barrel outlet and axe designed to safely pass the peak flow from the 10-year, 24-hour storm event, without discharging from the emergency spillway in accordance with Rule 4.05.9[2][b]. Pond 012 has a 5 foot tall perforated CMP riser. The inlet to each principal spillway is protected by a wire-mesh trash rack. The emergenry spillways consist of a trapezoidal channel with 3H:1V side slopes. The outslope of the spillways will be armored with rock riprap. The emergency spillways are designed to safely pass the peak flow from the 25-year, 24-hour storm event while maintaining one (1) foot of freeboard in accordance with Rule 4.05.9[2] [c] [ii]. The spillways are conservatively designed assuming the principal spillway is clogged and the water level is at the invert level of the emergency spillway prior to the storm event. Refer to Exhibits 13-12.2, 13-12.3, 13-12.4 and 13-12.7 for spillway designs. All ponds will have a volume of less than 20 ac-ft as measured from the invert of the emergency spillway to the original ground surface. Pond 012 is partially incised, which accounts for its total contained volume exceeding 20 ac-ft. (refer to Exhibit 13-12.2, Proposed Pond 012 Design). The embankments will be constructed such that the height from the upstream toe (original ground) to the emergency spillway invert will be 20 feet or less. The embankments will be constructed with 3H:1V slopes and a top width of 15 feet. All embankment crests and outslopes will be vegetated with the approved temporary seed mix (see Tab 22, Revegetation Plan). Stability analyses were performed for each pond (see Attachment 13-13, Sedimentation Pond 012 Stability Analysis; Attachment 13-15, Sedimentation Montgomery Watran Mining Group * 165 S. Union Baulevarc~ Suite 460 * I~rkemaod, Colorado 80228 * (303) 763-5140 'x_37 Revised 08/08