2021-07-28_PERMIT FILE - C1981019A

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Appendix Exh. 7-14ET East Taylor Pond and Permanent Channels The location of the East Taylor Pond is presented on Map 12. The profiles of the associated permanent channels associated with the East Taylor Pond watershed are presented on Map 33. These channels consist of the Taylor Ditch, the East Taylor Ditch the Taylor Tributary Ditch, several terrace ditches, and their respective design information is presented in this exhibit. The as-built configuration for the East Taylor Pond is presented on Figure Exh. 7-14ET-1, and Figure Exh. 7-14ET-2 provides the breakdown of drainage areas and hydrologic conditions for this sediment pond in the post mining condition. Figure Exh. 7-14ET-3 provides as-built information on the three stockponds that are constructed in the permanent channels to help reduce peak flows and provide a water source to support the post mine land use. Exhibit 7, Item 14 in Volume 2D describes the hydrologic methodology used in sediment pond and post mine channel assumptions. Runoff curve numbers assigned to the undisturbed and reclaimed lands in various stages of reclamation have been selected in accordance with Table 1 in the Introductory Text for Exhibit 7 in Volume 2D. For channels protected by a riprap liner, selection of minimum riprap size is done using the Simons/OSM method in SEDCADTM. For channels to be protected by a vegetative liner, the permissible velocities are also determined using SEDCADTM routines. East Taylor Pond The following pages present the results of the SEDCADTM models for the hydrologic conditions under the post mining condition. At this stage the oldest reclamation is on the northern extent of the reclaimed West Pit, and the younger (topsoil and seeded) reclamation is the southern reaches of the East Taylor Pond watershed. The SEDCADTM model herein provides the results of the 10 year 24 hour design storm and demonstrates the East Taylor Pond will meet the applicable settleable solids standard under this modeled storm event. The second SEDCADTM model demonstrates that the East Taylor Pond emergency spillway elevation is capable of containing the 25 year 24 hour storm. The final post mining topographic surface and the final locations of the permanent drainage channels as presented on Map 12 were used to model the watershed for the post- mining condition. Three in-stream stock ponds (TD-1, TD-2, and ETD-1) are included in the permanent channels to decrease peak flows from the modeled storm event, and to provide a water source to support the post-mining land use. An as-built of each stock pond in the East Taylor Pond watershed are provided on Figure Exh. 7-20ET-3. Also included in the models for the East Taylor Pond is flow from the East Taylor Seep. Currently, the East Taylor Seep is routed through a french drain and ultimately to a pipe which collects the flows and discharges it into the inlet of the East Taylor Pond. Exh. 7-ET-2 Revision Date: 3/24/21 Revision No.: TR-145