2015-09-09_PERMIT FILE - C1981019A

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"null" modeling node are 0.0 ml/1. The 25 year, 24 hour storm does not engage the emergency spillway and peaks at elevation 7473.22. For the post mining case, 10 year, 24 hour storm produces 7.3 acre feet of runoff at the West Taylor Sedimentation pond. As summarized in Table 4, peak reservoir stage while passing this storm is at elevation 7472.38, about 1.38 feet above the overflow of the primary (drop inlet) spillway and 3.62 feet below the invert of the emergency spillway. Settleable solids released from the pond in the downstream "null" modeling node are 0.0 ml/1. The 25 year, 24 hour storm barely engages the emergency spillway and peaks at elevation 7476.24, about 0.24 feet above the outlet. The following Items accompany this submittal: Figures: • Figure IC -4, West Taylor Pond, Drainage Areas, Active Mining Case page Exh.7-20C-5 • Figure 1C-5, West Taylor Pond, Subwatersheds Active Mining Case, page Exh. 7-20C-6 • Figure IC -6, West Taylor Pond, Drainage Areas, Post Mining Case, page Exh. 7-20C-7 • Figure 1C-7, West Taylor Pond, Subwatersheds, Post Mining Case, page Exh. 7-20C-8 SEDCAD Model output results: • SEDCAD model for Active pit, 10 Year -24 Hour storm, page Exh. 7-20C-9 • SEDCAD model for Active pit, 25 Year -24 Hour storm, page Exh. 7-20C-23 • SEDCAD model for PMT surface, 10 Year -24 Hour storm, page Exh. 7-20C-34 • SEDCAD model for PMT surface, 25 Year -24 Hour storm, page Exh. 7-20C-62 ENGINEERING CERTIFICATION I am a Licensed Professional Engineer in the State of Colorado and a representative of Environmental Solutions, Inc., P. O. Box 2996, Cheyenne Wyoming. The information contained in this document was provided by Colowyo Coal Company. Being familiar with the Colowyo operation and the coal permitting process in Colorado, the information contained herein is reasonable and correct to the best of my experience. .E. No. 32257 Exh. 7-20C-2 Revision Date: 06/15/15 Revision No.: TR -105