2024-08-29_PERMIT FILE - C1980007 (2)

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West Elk Mine 2.05-40 Rev. 11/04, 03/06, 04/06 & 05/06- PR10; 08/09- TR118; 08/09-TR119; 09/09- MR357; 01/10- TR120; 10/12- MR-388 Prior to the disturbance of the area for surface construction at West Elk Mine, four sedimentation ponds and associated collection structures were constructed to effectively retain runoff from the area to be disturbed. The other ponds were developed prior to the use of the old Bear Mine area; construction of the Lower Refuse Pile, formerly referred to as the U.S. Steel laydown area; construction of the Sylvester Gulch Facilities area; and construction of the RPE area. Prior to construction, topsoil was salvaged from all construction areas, stockpiled, and/or applied to slopes and cuts as necessary for reclamation. Exterior slopes of sedimentation ponds at the main mine facilities were reclaimed with a fast growing vegetative cover after they were constructed in order to prevent excessive erosion of the embankments. The cross-section of each sedimentation pond is given in Exhibit 66. Sedimentation pond designs are provided in Exhibit 42, Exhibit 43, Exhibit 44, Exhibit 46, Exhibit 47 and Exhibit 66. An emergency spillway has been provided for each pond, which will safely pass the peak runoff from a precipitation event with a 25-year recurrence interval or larger (100-year for FW-2 (formerly MB-1) and former pond MB-2R). The RPE pond has been designed to completely contain the runoff from a 100-year, 24-hour storm event. See designs for the RPE pond in Exhibit 70. Small Area Exemptions Small area exemption (SAE) demonstrations for the areas shown on Map 54, Map 54A, and Map 54B are provided in Exhibit 66. Discharges will meet State and Federal water quality requirements. No mixing with underground mine water occurs in these areas. Based on professional judgment, MCC believes that applicable effluent limitations will not be exceeded. Periodically, MCC will review the conditions of best management practices recommended by the small area exemption demonstrations and assure they are functioning. Design The specific size and capacity of any particular sedimentation pond are presented on Map 54 and Map 54B and are summarized in Exhibit 66. Stability analyses are presented in Exhibit 44. Exhibit 45 shows the approval by the Chief of Dam Safety, Division of Water Resources, of Ponds FW-1 and FW-2 (formerly pond MB-1). Fresh Water Ponds The design for the fresh water pond FW-1 is shown in Exhibit 43 and in Exhibit 44, Design Report. The fresh water pond FW-1 at West Elk Mine is approximately 10 acre-feet in capacity. With the construction of pond MB-5E, the stormwater runoff control functions as well as water storage capacity of former sediment pond MB-1 are handled in pond MB-5E. This allowed the existing pond (formerly MB-1) to be converted and utilized as freshwater pond FW- 2. Both FW-1 and FW-2 store water that is pumped from the North Fork of the Gunnison River. These freshwater ponds supply raw water for potable use, dust suppression, and the fire