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Appendix Exh. 7-14WA <br /> Work Area Pond and Temporary Ditches <br /> The location of the Work Area Pond is presented on Map 12. The as-built configuration for the <br /> Work Area Pond is presented on Figure Exh. 7-14WA-1, and Figure Exh. 7-14WA-2 provides <br /> the breakdown of drainage areas and hydrologic conditions for this sediment pond in the post <br /> mining condition. <br /> Exhibit 7, Item 14 in Volume 2D describes the hydrologic methodology used in sediment pond <br /> and post mine channel assumptions. Runoff curve numbers assigned to the undisturbed and <br /> reclaimed lands in various stages of reclamation have been selected in accordance with Table 1 <br /> in the Introductory Text for Exhibit 7 in Volume 2D. For channels protected by a riprap liner, <br /> selection of minimum riprap size is done using the Simons/OSM method in SEDCADTM. For <br /> channels to be protected by a vegetative liner, the permissible velocities are also determined <br /> using SEDCADTM routines. <br /> Work Area Pond <br /> The following pages present the results of the SEDCADTM models for a conservative model <br /> conditions under the post mining condition. At this stage, the majority of the Colowyo facilities <br /> area is topsoil, seeded, does not have any vegetative growth, and is fully reporting to the Work <br /> Area Pond. <br /> The SEDCADTM model herein provides the results of the 100 year 24 hour design storm and <br /> demonstrates the Work Area Pond will fully contain the model storm event below the emergency <br /> spillway. <br /> The final post mining topographic surface as presented on Map 12 was used to model the <br /> watershed for the post-mining condition. <br /> In summary, the post mining case at the Work Area Pond, the 100-year, 24-hour storm produces <br /> 8.16-acre feet of runoff. The storm peaks at the 7,153.17 elevation which is well below the <br /> emergency spillway elevation of 7,157'. <br /> Exh. 7-20WA-1 Revision Date: 1/6/21 <br /> Revision No.: TR-146 <br />