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Wes! Elk Mine <br />The l0-yeaz, 24 hour storm runoff design was adopted in accordance with CMLRB regulations. <br />• The Revised Universal Soil Loss Equation (RUBLE) 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 />inside dimensions of 24' in length, 10' in width, and 5' in depth, and can contain 600 ft.' of <br />sediment. <br />A system of ditches and culverts has been designed to collect runoff from the 10-year, 24-hour or <br />larger storm event and direct it to the runoff ponds. Although not required by CMLRB regulations, <br />most of the haul and access roads located within the main mine facilities azea are drained to <br />sedimentation ponds. An exception is the Sylvester Gulch haul/access road; however, best <br />management practicesfor stormwatertreatmentwill be utilized. Modificationsto the original mine <br />pond and ditch system can be found in Exhibit 48 and Exhibit 66. Ditches and culverts associated <br />with the RPE area are contained in Exhibit 70. Ditches and culverts are shown on Maps 54, 54A <br />and 54B. <br />Combined ditch flows are summarized for the system as they progress toward the runoff ponds. <br />Ditch and culvert specificationsare listed on Table 44, Exhibit 66. A summary table of inflows and <br />volumes for each pond is presented in Table 42 and in Exhibit 66. <br />The hydrologic parameters for watershed and subwatershed basins are summarized on Table 43 in <br />Exhibit 66. Documentation of specific parameters such as curve number, rainfall and time of <br />• concentration aze also found in Exhibit 66. This information for the RPE pond is located in Exhibit <br />70. <br />Miscellaneous Sediment Control Facilities <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) fora 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 <br />66. <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 />has been designed to completely contain the runoff from a 100-year, 24-hour storm event. The <br />design detail for this pond, the clean water diversion ditches and sediment ditches can be found in <br />Exhibit 70. <br />DCW-2, the ditch immediately south of the haul road above the Lower Refuse Pile, serves as the <br />clean water diversion ditch for the Lower Refuse Pile. It diverts undisturbed runoff from the Lower <br />Refuse disposal area and is discharged into sediment pond MB-2R. Runoff from the Lower Refuse <br />• Pile is conveyed to sediment pond MB-2R via perimeter ditches D2R-1, D2R-la, and D2R-3, <br />2.05-30 Revised Jan /996 R,V'03: Revised Nav. 1996 PR07; Revised Jan. 1997 TRi9; Revised Jul. 1991 TR81: Revised lun. 1999 TR90 <br />