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~• Sediment pond MB-2R is designed to accept mine water and storm water runoff. This pond also accepts runoff from the Lower Refuse Pile and treated discharge from the Waste Water Treatment Plant. MB-2R is lined with a geotextile liner. There are four sediment traps that water flows through prior to entering MB-2R. Two aze neaz the breaker building to pre-treat (settle) wash-down water from the conveyors, reclaim tunnel, and other similaz facilities. The third and forth sediment traps are located immediately above the western and eastern inlet to the ponds. The pond has been designed to store sediment for three veazs. Other than the increased amount of sediment that resulted from the lazge mine water inflow event in 1997, MCC's experience has been that the pond does not require cleaning that often. The pond was last cleaned of sediment during the fourth quarter of 1998. A 48-inch;riser pipe serves as the primary spillway for MB-2R, and contains three inlets at different elevations. The bottom two inlets aze gated for controlled discharges, while the highest inlet (the top of the riser pipe) is open. The middle inlet serves as the primary discharge. The emergency spillway is anopen-channel, rock lined spillway. MB-2R is sized to contain the 100-yeaz, 24-hour storm event, and/or MCC's water right for this pond. Piping is in place to allow water from MB-2R to be conveyed to the Raw Water Intake for mine water use. Sediment pond MB-3 is designed to accept storm water runoff and wash down water from the silos. A sediment trap has been constructed above the inlet to MB-3. The pond was designed to • contain three years of sediment, but MCC's experience has been that the pond does not require cleaning that often. This pond was last cleaned during the third! quarter of 1998. This pond is also lined with a geotextile liner. There aze two gated inlets at different elevations that serve as primary dischazge. The emergency spillway is anopen-channel, rock-lined spillway. MB-3 has been sized to contain the 25-yeaz storm event and hold MCC's storage right. Sediment pond MB-4 has been designed to accommodate storm water runoff and wash-down water from the train loadout facility. The sediment control system was redesigned and constructed in 1998 and 1999. The new system includes a concrete sediment trap, an oil skimmer, and a concrete sediment pond. In addition, an oil catckiment trench was constructed to capture lazger spills of hydraulic oil. Wash down water is piped directly to the sediment trap. The pond was designed to hold three yeazs of sediment that could be generated during a storm event. As the pond has just been constructed, MCC cannot evaluate the frequency of cleaning that may be required. The pond is designed to contain the runoff volume from a 10-yeaz, 24-hour storm event. The primary dischazge structure is a gated HDPE pipe. The emergency spillway is also a HDPE pipe, but is not gated. ~. DQB-d 7.05-32 November 1004 PRII