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West EIk Mine <br />pond has been designed to store sediment for three years. Other than the increased amount of <br />sediment that resulted from the large 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 are 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 discharge. 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 discharge. The emergency spillway is anopen-channel, rock-lined spillway. MB-3 has <br />been sized to contain the 25-yeaz 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 to <br />capture lazger 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 />cleaning that may be required. The pond is designed to contain the runoff volume from a 10- <br />yeaz, 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 dischazged only once a year. The principal <br />spillway is a gated pipe, and the emergency spillway is anopen-channel, rock-lined spillway. <br />This pond was designed to store three-yeazs of sediment. The pond has never been cleaned as <br />the sediment generated is less than what was predicted in the SEDCAD model. MB-5 is sized to <br />hold the runoff from a 25-year, 24-hour storm event. <br />• <br />1.03-31 Revised June 2003 PRIO; Rev. Januay 2006; Rev. Minch 1006; Rev. April 2006 PRIG, Moy 1006 PRIG <br />