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<br />West Elk Mine <br /> <br />The CDRMS requirements for the emergency spillway sizing are 25-year, 24-hour storm flows, or <br />100-year, 24-hour storm flows, depending on the size of the structure. The spillways for MB-3 and <br />MB-4 were sized based on the 25-year, 24-hour storm, while MB-5E and SG-1 were sized for the <br />100-year, 24-hour storm event in accordance with the requirements of the State Engineer. Drainage <br />basins for the spillway sizing are shown on Map 54 and 54A, Sediment and Drainage Control <br />Facilities. The RPE pond has been designed to completely contain the runoff from a 100-year, 24- <br />hour storm event. Designs are included in Exhibit 70. <br /> <br />The 10-year, 24-hour storm runoff design was adopted in accordance with CDRMS regulations. <br />The Revised Universal Soil Loss Equation (RUSLE) was used to predict the sediment yield from <br />three years of runoff. MCC will maintain the ponds in compliance with the designs to effect <br />discharge in compliance with effluent limitations. In some cases, MCC has installed concrete <br />sediment traps above the pond inlets to facilitate sediment removal. These traps typically have <br />3 <br />inside dimensions of 24 feet in length, 10 feet in width, and 5 feet in depth, and can contain 600 ft. <br />of sediment. <br /> <br />A system of ditches and culverts has been designed to collect runoff from the 10-year, 24-hour or larger <br />storm event and direct it to the runoff ponds. Although not required by CDRMS regulations, most of the <br />haul and access roads located within the main mine facilities area are drained to sedimentation ponds. <br />An exception is the Sylvester Gulch haul/access road; however, best management practices for <br />stormwater treatment are utilized-pipe were <br />installed to aid in stormwater sampling and flow measurements at six (6) existing stormwater culverts as <br />shown on Map 54B. Modifications to the original mine pond and ditch systems can be found in Exhibit <br />48 and Exhibit 66. Ditches and culverts associated with the RPE area are contained in Exhibit 70. <br />Ditches and culverts are shown on Maps 54, 54A and 54B. <br /> <br />Combined ditch flows are summarized for the system as they progress toward the runoff ponds. Ditch <br />and culvert specifications are listed on Exhibit 66 tables. A summary table of inflows and volumes for <br />each pond are also presented in the tables in Exhibit 66. <br /> <br />The hydrologic parameters for watershed and sub-watershed basins are summarized on Table 43 in <br />Exhibit 66. Documentation of specific parameters such as curve number, rainfall and time of <br />concentration are also found in Exhibit 66. This information for the RPE pond is located in Exhibit 70. <br /> <br />Miscellaneous Sediment Control Facilities <br /> <br />The railroad loadout facility has been treated independently of the other surface facilities. The <br />loadout is located across the river from the other surface facilities and, therefore, must have its own <br />sediment control. The sediment control is a pond designed (sized) for a 25-year, 24-hour storm <br />event and to accommodate wash-down water from the train load-out facility. Pond MB-4 was <br />relocated in 1998 from the east side of the train load-out to an area west of the load-out between the <br />two sets of tracks. The relocated sediment pond is constructed with concrete and is preceded by an <br />oil skimmer and a sediment trap. The current design detail for this pond can be found in Exhibit 66. <br /> <br />The RPE area has also been treated independently of the other surface facilities. The RPE area is <br />located to the east of the lower refuse disposal area and east of Sylvester Gulch. The sediment pond <br />2.05-32 Rev. 06/05, 01/06, 03/06, 04/06 & 05/06- PR10; 01/09- MR350; 04/09- TR116; 05/09- MR354; 08/09- TR119; MR443- 5/20 <br /> <br />