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Mountain Coal Company <br />West Elk Mine <br />Exhibit 51 <br />Lower Refuse Pile <br />TABLE 12. 25-Year, 24-Hour Storm Peak Discharge <br />Phase Peak Discharge (cfs) <br />I 8.2 <br />II 9.4 <br />III 11:2 <br />I V /21.93 '? <br />The existing outlet structure is composed 9f'two inlet structures along a 24-inch <br />corrugated metal pipe. The first inlet po 1 consists of a 12-inch valve at elevation <br />6107 feet. The inlet was not analyzed fo discharge capability since the valve is used <br />for drainage. The upper emergency s tllway consists of 24-inch CMP opening at <br />elevation 6109 feet, with a final a elevation o 6111 feet. The pond relies <br />primarily on storage to handle flgw from a 25-year 24- our storm event per Rule <br />4:05.6(6). <br />A hydraulic study was <br />inlet capacity of the s; <br />indicates that the cur <br />6110.5 feet and, theref <br />as required by the C~ <br />sedimentation basin <br />3 ~ ~ {~~or`c., <br />6.4 <br />~erfo ed using weir and orifice equations to determine the <br />ate and Bernoulii's equation for outlet control. The study <br />outlet structure has a capacity of 16.5 fps at elevation <br />the current system meets the required discharge standards <br />LRB. Therefore, no modifications to either the size of the <br />the outlet works is necessary for the lower refuse pile. <br />Clear Warr Ditch Design <br />The clear wat r ditch design was performed using the same ditch configuration and <br />methodolo stated in Section 6.2. The summary of the design for each phase is <br />shown on able 13 and states the phase, ditch location, peak discharge, velocity, <br />normal d th, and lining requirements. <br />v~~ ~ ~~~- <br />~Ilp/ <br />~R <br />