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Peabody Twentymile Coal Company 29515 Routt County Road #27 Oak Creek, CO 80467 970.879.3800 TCC's intent is to consistently maintain approximately 10.0 million gallons, or 30.7 acre-feet, of water in the 6MN Reservoir, to supply the mine water system. As designed, the Reservoir has sufficient additional capacity to provide buffer storage for another 1.0 million gallons, or 3.1 acre-feet, of emergency mine water storage to address any maintenance or emergency shut-downs of the pumping system, and 1.9 acre- feet (equivalent to the runoff from a 100-yeaz, 24-hour storm event) of runoff from the limited contributing watershed. At maximum water storage level (35.7 acre-feet), taking into account the incremental storage capacities outlined, reservoir freeboazd will be approximately 0.8 feet to the invert of the open-channel spillway, and 2.3 feet to the top of the embankment. The discharge pumping system for the 6MN Storage Reservoir has been designed with the capacity to dewater the design storm-water storage volume in less than 12 hours. Any discharge of stored mine or stotmwater from the 6MN Storage Reservoir, will be directly to the mine water system, with no dischazge through the emergency spillway to natural drainage. While it will not be utilized during normal operations or under design storm conditions, the open-channel spillway and the lower portion of the stormwater diversion channel aze designed to safely pass the peak discharge (approximately 125.5 cfs), and the total runoff, respectively, from the design storm event. As part of the 6MN Storage Reservoir project, TCC will establish a new pipeline running approximately 6,000 feet from the 10-Right Dewatering pipeline to the 6MN Storage Reservoir. The pipeline will be constructed of 10-inch HDPE pipe, buried to a depth of approximately six feet, with one sub-grade crossing (bored under) of Fish Creek. In conjunction with this crossing, TCC requests approval of a waiver to the stream buffer zone protection requirements (Rule 4.05.18) for temporary pipeline construction disturbance within the buffer zone. The proposed temporary pipeline construction disturbance will not cause or contribute to violation of applicable water quality standazds; adversely affect water quality or quantity, and will not involve any temporary diversion activities. On the edge of the Reservoir, neaz the embankment, a pump platform will be constructed, with a suspended 50 HP high-capacity submersible pump, pumping mine water from the Reservoir at a rate of up to 1,000 gpm to the Million-Gallon Tank at 6MN (MR06-210), which is set-up to gravity-feed to the mine water system through the existing mine water utility borehole. The approximately 1,400 foot pipeline from the 6MN Reservoir to the Million-Gallon Tank will also be 10-inch HDPE pipe buried to a depth of approximately six feet within the previously disturbed 6MN road right-of--way. Pipeline construction will involve removing and temporarily windrowing soil materials along the edge of the pipeline alignment; excavation and temporary placement of the excavated material on the opposite side of the trench; bedding, placement, connection, and testing of the pipeline; controlled backfilling and compaction of the excavated material over the pipeline; and replacement, grading, and reseeding of the soil material over pipeline disturbance areas. In order to assure adequate and consistent water quality for the feed to the mine water system, the 6MN Mine Water Storage Reservoir installation will include some basic water treatment measures, potentially including one or more aerators, floating baffles within the pond, and a simple filtration system in the discharge pipeline between the Reservoir and the Million-Gallon Tank. If it is determined that additional treatment measures are necessary, any significant modifications will be addressed by a future revision. G:\Environmentsl\REVISION\TECH-RV\TR07-61 6MN Storage Reservotr\TR07-61 6MN Storage Resv 77, Rl.doc