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West Elk Mine <br />MB-3 <br />Sediment pond MB-3 is designed to accept storm water runoff and wash down water from the <br />coal storage silos. A sediment trap has been constructed above the inlet to MB-3. The pond <br />was designed to contain three years of sediment, but MCC's experience has been that the pond <br />has not required cleaning that often. This pond is also lined with a geotextile liner. There are <br />two gated inlets at different elevations that serve as primary discharge. The emergency <br />spillway is an open-channel, rock-lined spillway. MB-3 has been sized to contain the 25-year <br />storm event and hold MCC's water 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. The pond is designed to contain the runoff volume from a 14-year, 24-hour <br />storm event. The primary discharge structure is a gated HDPE pipe. The emergency spillway <br />is also a HDPE pipe, but is not gated. <br />MB-5E <br />Sediment pond MB-5E is designed primarily for stormwater runoff, but can also accept mine <br />water discharges, and store some of MCC's adjudicated water storage rights. No mine water <br />discharges from the F-seam portals have occurred since the mine water treatment pumps and <br />ponds were constructed near the Sylvester Gulch dewatering pump station. This pond also <br />accepts runoff from the treated discharge from the Wastewater Treatment Plant. <br />There are several sediment traps that water flows through prior to entering pond MB-5E. Two <br />are near the breaker building to pre-treat (settle) wash-down water from the conveyors, reclaim <br />tunnel, and other similar facilities. Others are located near the northeast and northwest corners <br />of the LRP perimeter ditches and another is located before the large inlet pipe that directs <br />flows to the pond. <br />MB-5E is comprised of two ponds (or cells) lined with a 4" to 6" clay liner. Long-term <br />operating experience has shown that clay liners have proven to be much more durable for <br />regular maintenance and pond cleaning activities with heavy equipment, as HDPE and <br />geotextile liners easily tear and leak and are difficult and expensive to repair. Pond MB-5E <br />was designed so that each pond cell can be operated independently. One cell of pond MB-5E <br />is generally utilized to handle stormwater runoff while the other cell is closed and left empty <br />and ready to accept stormwater when the other cell has filled or for water storage, if needed. <br />When the open, active pond has filled to near the maximum fill level, the inlet to the empty <br />pond is opened and the full pond inlet is closed. The full pond is then discharged as described <br />2.115-34 Rev. 11010,01%, /131116.1141P6 $ OV& PRN1: 0110- MR350. 04109- TRI16:: 0510- MR354; 0811)9- TR1 f9