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West Elk Mine <br />• emergency spillway is anopen-channel, rock-lined spillway. MB-1 is lined with a HDPE liner <br />that was installed in eazly 1998. The pond has been designed to hold three yeazs of sediment. <br />Other than the increased amount of sediment that resulted from the large mine water inflow <br />events in 1997, MCC's experience has been that the pond does not have to be cleaned of <br />sediment that often. MB-1 was last cleaned during the fourth quarter of 1997. MB-1 is sized to <br />contain the 100-year, 24-hour storm event, and/or MCC's water right for this pond. Piping is in <br />place to allow water from MB-1 to be pumped to FW-1 for mine water use. <br />MB-2R <br /> <br />Sediment pond MB-2R is designed to accept mine water and storm water runoff. This pond also <br />accepts runoff from the Lower Refuse Pile and treated discharge from the Wastewater Treatment <br />Plant. MB-2R is lined with a geotextile liner. There aze four sediment traps that water flows <br />through prior to entering MB-2R. Two aze neaz the breaker building to pre-treat (settle) wash- <br />down water from the conveyors, reclaim tunnel, and other similaz facilities. The third and forth <br />sediment traps are located immediately above the western and eastern inlet to the ponds. The <br />pond has been designed to store sediment for three yeazs. Other than the increased amount of <br />sediment that resulted from the lazge mine water inflow event in 1997, MCC's experience has <br />been that the pond does not require cleaning that often. The pond was last cleaned of sediment <br />during the fourth quarter of 1998. A 48-inch riser pipe serves as the primary spillway for MB- <br />2R, and contains three inlets at different elevations. The bottom two inlets aze gated for <br />controlled discharges, while the highest inlet (the top of the riser pipe) is open. The middle inlet <br />serves as the primary dischazge. The emergency spillway is anopen-channel, rock lined <br />spillway. MB-2R is sized to contain the 100-year, 24-hour storm event, and/or MCC's water <br />right for this pond. Piping is in place to allow water from MB-2R to be conveyed to the Raw <br />Water Intake for mine water use. <br />MB-3 <br />Sediment pond MB-3 is designed to accept storm water runoff and wash down water from the <br />silos. A sediment trap has been constructed above the inlet to MB-3. The pond was designed to <br />contain three years of sediment, but MCC's experience has been that the pond does not require <br />cleaning that often. This pond was last cleaned during the third quarter of 1998. This pond is <br />also lined with a geotextile liner. There are two gated inlets at different elevations that serve as <br />primary dischazge. The emergency spillway is anopen-channel, rock-lined spillway. MB-3 has <br />been sized to contain the 25-year storm event and hold MCC's storage right. <br />MB-4 <br />Sediment pond MB-4 has been designed to accommodate storm water runoff and wash-down <br />water from the train loadout facility. The sediment control system was redesigned and <br />constrncted in 1998 and 1999. The new system includes a concrete sediment trap, an oil <br />skimmer, and a concrete sediment pond. In addition, an oil catchment trench was constructed to <br />capture larger spills of hydraulic oil. Wash down water is piped directly to the sediment trap. <br />• The pond was designed to hold three yeazs of sediment that could be generated during a storm <br />event. As the pond has recently been constructed, MCC cannot evaluate the frequency of <br />2.05-29 Revised June 2005 PRI G <br />