2008-01-16_PERMIT FILE - C1994082A (6)

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I~eG~rm~~ 1J%9 Yaa,rtMine * 13-12 Drainage and Sediment CantmlPlan •S • TABLE 13-12.4 PRACTICE FACTOR Surface Surface Type Practice Practice Factor Undisturbed Varies None 1.0 Disturbed Topsoil Stripped/Spoil Rough and Irregular 1.0/0.8 4.0 PONDS x111 ponds are designed to treat the runoff produced from the 10-year, 24-hour storm event in accordance with Rule 4.05.6. The ponds were designed utilizing the SEDCAD4 computer model. The input parameters and results are presented in the SEDCAD4 printouts located in Appendix 13-12.1, Sediment Ponds SEDCAD4 Results, and summarized in Table 13-12.5, Yoast Mine Sedimentation Pond Summary. 'h'he location of Ponds 012, 013 and 014 and then corresponding watersheds are shown on Exhibit 13-12.1, 1"oast i\fine \\ atershed. A simplistic 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. Tlis approach resulted in a conservative design for each pond. Pond and embankment configurations for Ponds 012, 013 and 014 can be found on ExhiUitsl3-12.2, Proposed Pond 012 Design, 13-12.3, Proposed Pond 013 Design, and 13- 12.4, Proposed Pond 014 Design, respectively. Pond 012A v~~ill be used to assist Pond 012 to treat the runoff and sediment from a portion of the Sout1~ Pit mine area. The location of Pond 012A is shown on Exhibit 12-1, Operations Plan; the contributing watershed is shown on Exhibit 20-2, Postmining Topography Map. Runoff and scctimentation calculations were based on June 2007 landscape and vegetation conditions. As presented in the Toast 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 is presented on Exhibit 13-12.7, Pond 012A Design. x111 ponds have principal and emergency spillways. The principal spillways for ponds 012A, 013 and 014 consists of a 5 foot tall, CMP riser, with an accompanying CMP barrel outlet and are designed to safely pass the pcah flrnv from the 10-year, 24-hour storm event, without discharging from the emergency spillway. I'~:,ncl O l? has a ~ f~~ot tall perforated CMP riser. The inlet to the principal spillway is protected by a wire- mesli trash rich. '1 he emergency 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. 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 incised, which accounts for its total contained volume exceeding 20 ac-(t. (rcfrr to I?shibit 13-12.2, Proposed Pond 012 Design) Tic rmbanl:nu~nts 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. .-111 embanl~nent crests and outslopes will be vegetated with the approved temporary seed nix. A stability analysis for Pond 02 has been performed (see Attachment 13-13, Sedimentation Pond 012 Stabilir5~ Analysis); the embankment will be constructed and certified as described. A1nni~ni~r~~~ 6C' atron ~l7ining Group * 165 S. Union Ban/evar~l Snite 460 * Lakemoor~ Cola~ado 802?8 * (303) 763-5140 TR-i6 Revised 08/07