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West Elk Mine <br />Sediment pond MB-2R is designed to accept mine water and storm water runoff. This pond <br />also accepts runoff from the Lower Refuse Pile and treated discharge from the Wastewater <br />Treatment Plant. MB-2R is lined with a geotextile liner. There are four sediment traps that <br />water flows through prior to entering MB-2R. Two are near the breaker building to pre-treat <br />(settle) wash-down water from the conveyors, reclaim tunnel, and other similar facilities. The <br />third and forth sediment traps are located immediately above the western and eastern inlet to <br />the ponds. The pond has been designed to store sediment for three years. Other than the <br />increased amount of sediment that resulted from the large mine water inflow event in 1997, <br />MCC's experience has been that the pond does not require cleaning that often. The pond was <br />last cleaned of sediment during the fourth quarter of 1998. A 48-inch riser pipe serves as the <br />primary spillway for MB-2R, and contains three inlets at different elevations. The bottom two <br />inlets are gated for controlled discharges, while the highest inlet (the top of the riser pipe) is <br />open. The middle inlet serves as the primary discharge. The emergency spillway is an open- <br />channel, rock lined spillway. MB-2R is sized to contain the 100-year, 24-hour storm event, <br />and/or MCC's water right for this pond. Piping is in place to allow water from MB-2R to be <br />conveyed to the Raw 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 <br />to contain three years of sediment, but MCC's experience has been that the pond does not <br />require cleaning that often. This pond was last cleaned during the third quarter of 1998. This <br />pond is also lined with a geotextile liner. There are two gated inlets at different elevations that <br />serve as primary discharge. The emergency spillway is an open-channel, rock-lined spillway. <br />MB-3 has 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 />constructed 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 <br />to capture larger spills of hydraulic oil. Wash down water is piped directly to the sediment <br />trap. The pond was designed to hold three years of sediment that could be generated during a <br />storm event. As the pond has recently been constructed, MCC cannot evaluate the frequency <br />of cleaning that may be required. The pond is designed to contain the runoff volume from a <br />10-year, 24-hour storm event. The primary discharge structure is a gated HDPE pipe. The <br />emergency spillway is also a HDPE pipe, but is not gated. <br />MB-S <br />Sediment pond MB-5 has been designed to accommodate storm water runoff, and is located at <br />the old Bear No. 1 mine site. The pond usually is discharged only once a year. The principal <br />spillway is a gated pipe, and the emergency spillway is an open-channel, rock-lined spillway. <br />2.05-33 Revised June 2005 PRIO; Rev. January 1006; Rev. March 2006; Rev. Apri12006 PR10, May 2006 PRIO; Rev. January 2009 MR-350 <br />