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West Elk Mine <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 CDMG 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 hauVaccess road; however, best <br />management practices for stormwater treatment will be utilized. Modifications to 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 aze summarized for the system as they progress toward the runoff ponds. <br />Ditch and culvert specifications aze 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 sub-watershed basins aze 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 <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-yeaz, 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 azea 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 />The RPE azea 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 runaff from a 100-yeaz, 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 bower Refuse Pile. It diverts undisturbed runoff from the Lower <br />Refuse disposal azea and is dischazged 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-1 a, and D2R-3, which <br />aze all sized for the 100-year, 24-hour storm event. <br />During construction of the West Elk Mine, a spring was located on the site where the substation was <br />to be built. hi order to stabilize the substation pad, a french drain system and collection pipe were <br />constructed to dewater it. As shown in Exhibit 43 and on Map 54, a 6-inch PVC pipe collects the <br />water and drains it into culvert C1-6A. MCC has designed and constructed several other french <br />drains azound the mine site, as approved by the CDMG, to improve stability. These french drains <br />aze shown on Map 54. Sediment traps were constructed below the breaker building to pre-treat <br />(i.e., settle) wash-down water prior to flowing down to pond MB-2R. The locations of these <br />1.05-30 Revised June 2005 PRIG; Rev. January 2006; Rev. Minch 1006; Rev. Apri11006 PR/0, May 1006 PRIO <br />