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Scutnn - 2.05.3 and modification of Sedimentation Pond B and the Substation No. 3 Sedimentation Pond and • associated ditches were prepared or modified 6y Thomas E. Ieidich, P.E. No. 31459. Detailed design plans for Sedimentation Pond C and the associated ditches and culverts for both the West ValleyFill and associated haul road were prepazed by or under the direction of Greg Eddy, P.E. No. 31270. These plans were reviewed and modified to address specific DMG concerns by lXrilliam P. Balaz, P.E. No. 17129. Detailed design plans for culvetting the middle portion of Elk Creek, the collection and diversion ditches and alternative sediment control measures implemented for the Elk Creek Mme surface facilities, and Sedimentation Pond D were prepared by or under the direction of Thomas E. Ixidich, P.E. No. 31459, and Daniel J. Keuscher, P.E. No. 33307. Mine Water Storage and Discharge -Mme workings in both the Sanbom Creek B Seam Mine and the Elk Creek D Seam Mme produce sufficient water that dewateting is required in conjunction with mine development and active mining operations. To the extent reasonably feasible, mine dewateting flows are routed to large underground sumps for temporary storage and to allow suspended solids in the water to settle out. Accumulated water is then recovered and pumped back into the mine water system for reuse. Any excess mine water which exceeds operational usage requiremenu and active storage capacityis discharged to the surface. For the Sanbom Creek Mtne, excess mine dewateting flows are pumped from the underground sump to an existing mine water settling pond designed to provide additional retention time to allow suspended solids to settle from the water prior to discharge to Sanbom Creek The mine dewatenng pond u a totally incised pond with a bottom elevation of 6,056 feet and a two-foot deep collettion ditch around the perimeter of the pond. The up- stream, interior sideslopes of the pond are 2Fi•1V. • The pond can be dewatered through a 2-inch dewateting pipe with an invett elevation of 6,060.5 feet, which effectively provides 4.5 feet of sediment storage. OMI visually monitors sediment accumulation in the mine pond annually during the third quarter. When the sediment in the pond reaches an average elevation of 6,059 feet, or 1.5 feet below the primary spillway invert, it will be cleaned out. A backhoe will be used to excavate the sediment and the sediment will be hauled to and placed in the active coal refuse and mine development waste disposal area. On completion of active mining operations in the Sanbom Creek Mme, it a anticipated that pumping will cease, the mine workings will be allowed to flood, and that the mine dewatering pond will be removed and the associated disturbance area reclaimed. Pond removal will involve removal of discharge structures, backfilling the pond basin, grading the pond area, replacing available soil material, and revegetating the regraded area Design information for the Sanbom Creek Mtne Dewatering Pond is provided in Exhibit 2.05-E3, Drainage and Sediment Control Plan, and pond design configuration is illustrated by the Sanbom Creek Mute Dewatering Pond Map, (Map 2.05-M- SI I). Dewatering flows from the Ells Creek D Seam Mute are expected to contain lower levek of suspended solids based on available water quality information and the design of the D Seam sump. Secondary containment in a pond will, therefore, probably not be necessary to meet applicable effluent standards. Any dewatering flows which exceed the attive capacity of the Elk Creek Mme underground sump will be pumped from the sump to the Elk Creek Mine head tank for temporary storage and reuse in the mine water system If flow volume exceeds operational requirements and the capacity of the storage tank, any excess dewatering flows will be discharged though an overflow valve and discharge line to Elk Creek . Sedimentation Ponds -Given that surface disturbance is limited by the underground mining operations, OMI utilizes alternative sediment control measures where reasonably feasible to both intercept and control drainage and sediment as close to it's source as possible and to m~r,im~~e further surface disturbance. For larger disturbance areas, however, this approach is not effective in PR04 2.05-33 Revised August 2000