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Blue Mountain Energy 3 Illustration 62 <br />Introduction <br />Blue Mountain Energy plans to combine the refuse disposals areas RP-234 and RP-5 into a single area to <br />be known as RP-2345. The original permitted refuse disposal areas are nearing their original permitted <br />configuration and there is continuing need for refuse disposal area. <br />In 2019, an unexpected change in coal processing waste moisture content occurred. Coal waste slurry <br />from the bottom of the clarifier used to be discharged into the old, sealed D Seam mine. That disposal <br />avenue unexpectedly ended, and the high moisture material had to be routed to the refuse piles. The <br />high moisture material must be spread out and dried before it can be properly compacted. <br />Fortunately, the refuse disposal area RP-A was approved at the end of 2019. Though it was originally <br />planned to serve the primary disposal needs as RP-234 and RP-5 were completed, the high moisture <br />material requires a significant surface area to dry out. This is especially true during the winter as the <br />material must be stored in low spaced out rows until spring when it can be spread and dried. The <br />surface area of all the current disposal areas is required to make it through the winter. Combining and <br />continuing use of the old disposal areas will facilitate the refuse drying process with minimal new <br />disturbance. <br />The valley between the original piles will be filled and the pile design height will be increased up to the <br />maximum as outlined in Illustration 42B. Terraces will be increased to 20 feet in width. <br />Hydrology <br />The reconfigured disposal area was modeled in SEDCAD 4. The structures are numerated, and the sub <br />watershed areas are delineated on the accompanying Map 165. Rainfall data is included in Appendix A. <br />Curve numbers previously calculated for refuse areas were used. SEDCAD results are included in <br />Appendices B, C and D. <br />The existing sediment ponds along with most of the existing ditches will be utilized. The ditches in the <br />valley will mostly be buried, but remaining portions will be slightly reconfigured to accommodate the <br />toe of the refuse slope. The main change to the existing structures will be the ditches to the south. <br />Rather than flowing down the valley between the two piles, there will be one continuous mild slope <br />erodible channel flowing east-northeast along the south perimeter of the combined piles. <br />The overall area is unchanged, but the additional mild sloped terraces attenuate the flow rate <br />significantly. More area flows to the RP-5 sediment pond, but the pond water elevation does not reach <br />the emergency spillway during the 100-year storm. The other sediment ponds receive less water than <br />before. No changes to the ponds or their outlet structures are required. The stage-storage and outlet <br />hydraulics curves can be found on maps 79, 80 and 80A. <br />All the existing structures that will continue to be utilized still have adequate capacity. The new <br />structures are the terrace channels and the ditch around the south perimeter. These new channels are <br />mildly sloping erodible channels not requiring rip rap. The acute junctions where a terrace meets the <br />next downstream channel will be wide and nearly flat acting as stilling basins. Rip rap has also been