2009-05-26_PERMIT FILE - C1980007A

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West Elk Mine This pond was designed to store three-years of sediment. The pond has never been cleaned as the sediment generated is less than what was predicted in the SEDCAD model. MB-5 is sized to hold the runoff from a 25-year, 24-hour storm event. SG-1 Sediment pond SG-1 was constructed in 1997 to accommodate storm water runoff from the pads associated with ventilation shafts #1 and #2, located in Sylvester Gulch. The pond treated construction water during construction of the shafts. The pond was designed to contain the 10-year, 24-hour runoff volume. The pond is lined with HDPE. The principal spillway consists of a channel of filter rock that filters the sediment prior to entering a slotted HDPE pipe, which then becomes a solid pipe. The system is an effective means to treat the water and the discharge pipe has been designed to remain open. However, it is usually valved closed to control discharge from the pond. The emergency spillway is an open-channel, rock- lined spillway. The pond was designed to hold three years of sediment. As the pond has recently been constructed, MCC cannot evaluate the frequency of cleaning that may be required. RPE Ponds The RPE ponds were also constructed during 1997 to accommodate storm water runoff and possible leachate from the Refuse Pile Expansion (RPE). The RPE ponds are essentially one pond with two cells, similar to pond MB-1. Water from the sediment ditch enters Cell A (the eastern cell). Water can be treated in this cell and discharged directly to the river through piping that connects the cell to the primary discharge structure in Cell B, or the water can be transferred over to Cell B for further treatment if necessary. The primary discharge is through a gated pipe. The emergency spillway is a pipe, but remains open. The pond has been designed to hold the runoff volume from a 100-year storm event. The pond was designed to hold three years of sediment that could be generated during a storm event. As the pond has recently been constructed, MCC cannot evaluate the frequency of cleaning that may be required. FW-1 Freshwater Pond-1 (FW-1) was originally designed to provide two months storage capacity for potable and domestic water uses at 250,000 tons per year production. At a projected production rate of 8.2 million tons per year, approximately 3.0 days of storage capacity is now provided. This pond has a capacity of ten acre-feet, an embankment height of 19.5 feet, and a surface area of 1.10 acres. The pond is located on the natural bench above the valley floor at an approximate elevation of 6,290 feet. 2.05-34 Revised June 2005 PRIO; Rev. January 2006; Rev. March 2006; Rev. April 2006 PRIO, May 2006 PRIO; Rev. January 2009 MR-350