2008-08-20_REVISION - C1982056 (3)

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Map 24 (sheet 2 of 3), Surface Facilities and Freshwater Systems. Related design information is provided in Exhibit 490, 6MN Mine Water Storage Reservoir - Design Drawings, including a design stability analysis for the pond embankment (also refer to detailed Reservoir description on pages 2.05-45.6f through 2.05-45.8). Because the proposed Reservoir storage volume is greater then 20 acre-feet, design and compliance documentation have also been submitted to the Mine Safety and Health Administration (MSHA) for review and approval. SMALL AREA EXEMPTIONS AND ALTERNATIVE SEDIMENT CONTROLS TCC has been granted several Small Area Exemptions (SAE's) within the permit area. Effective drainage and sedimentation control in these areas will be achieved through the use of a number of individual or combined methods, including gravel-surfacing; erosion control fabric or materials; berms; contour furrows; sediment traps; rock check dams; vegetative filters; the use of silt fences, straw wattles, or straw bales; or other approved methods. Rockdust Tank - An SAE for sedimentation control has been granted for the rockdust tank and truck access/unloading area. The total disturbance will be approximately 0.5 acres. Of this area, 0.3 acres will be filled with pit-run gravel, which acts as an infiltration screen for any overland flow associated with the rockdust tank and access/unloading area. Estimated peak flow from the area for the 10-year, 24-hour event is approximately 0.04 acre-feet. Runoff from the topsoil pile is controlled by a berm/swale/rock filter system. In addition to the infiltration screen, flow from the tank and unloading area is conveyed by means of swales and berms to a gravel filter. These controls, in conjunction with existing vegetation, will be sufficient to control runoff from the area as observed during previous inspections. Fish Creek Dewatering Site - At the dewatering site, sedimentation will be controlled by the use of alternate control systems such as filter fences, gravel filters, and existing vegetation. For the 0.5 ac stockpile located to the southwest of the pond, a berm will be established around the stockpile to direct runoff from the stockpile to the two gravel filters by the stockpile. This will effectively treat the estimated 0.02 acre-feet of runoff resulting from the 10-year, 24-hour event until vegetation is reestablished. Once this occurs, the berm and filters can be removed. The runoff from the 0.2 acre stockpile adjacent to the transformer will drain to the low area northeast of the stockpile where adequate vegetation exists to provide filtering and treatment of the water. The SAE is shown on Map 26, Fish Creek Borehole Area Facilities and Access Road. The collection ditch for the ponds and associated disturbed areas will be constructed with two gravel filters to act as a secondary sediment control measure. The gravel filters will be constructed of 3-inch minus washed gravel, and will be approximately 24 inches in width. The filters will be placed across the ditch and extend halfway up the sides of the ditch. A berm will be placed on the south side of the road leading into the control building. The berm will be located to keep drainage from this area from entering the discharge ditch. The berm will provide an area that can act as a sump to hold or direct water from the site. In reference to the boreholes and control building area, collection berms will be established downslope of the area to direct the estimated 0.12 of of runoff (from the 10-year, 24-hour event) to either the containment area to the west, or to the two rock filters on the north side. In order to provide access to the dewatering boreholes, the two light-use roads will be connected to form a pad between the wells. The available topsoil will be windrowed to the sides of the pad and will be stabilized with the approved seed mixture. The graveled pad and roads are within the confines of the 2.0 acre SAE area as shown on Map 26, Fish Creek Borehole and Facilities and Access Road. In reference to the boreholes and control building area, collection berms will be established downslope of the area to direct an estimated 0.12 acre-feet of runoff from the 10-year, 24-hour event to either the adequately-sized natural depression west of the area, or to a pair of rock filters on the north side. Fish Creek Ventilation Borehole and Dewatering Site (Revised - MR07-216) - Another SAE exists at the Fish Creek Ventilation Borehole/Dewatering Site. A vegetative filter will provide sediment control for the 0.6 acre area of disturbance. Until the vegetation becomes reestablished, however, the 0.06 acre-feet of runoff from the 10-year, 24-hour event will flow to the collection area around the Fish Creek Borehole ponds, where it will be controlled TR07-61 2.05-83 08/18/08