2019-10-18_GENERAL DOCUMENTS - C1981022

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by the Elk Creek Profiles, (Map 2. 05-M7), and the Postmining Topography Map and Cross-Sections, (Maps 2.05-M6 and 2.05-M7),placement of riprap materials, as required; replacement of available soil material on the upper channel slopes;and revegetation of both channel and sideslope areas. The reconstructed Elk Creek channel has been designed to safely pass the peak flows resulting from a 100 year, 24-hour storm event. The designed channel has 2H.•I V sideslopes, a 10-to 12-foot bottom width, and overall gradients consistent with both the original channel and the existing culvert. Channel design calculations for the reconstructed Elk Creek channel are included in Exhibit 2.05-E3, Drainage and Sediment Control Plan. Where the existing culvert does not sit on the original channel bottom, suitably sized riprap material will be placed and bedded in the reconstructed channel to minimize channel erosion. Riprap placement will extend approximately 3 to 4 feet up the channel sideslopes to minimize the potential for erosion from normal variations inflow levels. Riprap will be obtained from one or both existing permitted borrow sources along the Elk Creek road. Channel reconstruction work will be completed during late summer or early fall during seasonal low flow periods to the extent reasonably feasible to minimize impacts on Elk Creek and downstream on the North Fork of the Gunnison River. The sub grade coal stockpile reclaim tunnel is a reinforced concrete structure. This structure will be demolished and the rubblized demolition debris will be left in place. The resulting void will allow for sub grade placement ofdemolition debris from other structures within the Ells Creek Facilities area. Final overall grading of the facilities area and specifically the coal stockpile area and reconstructed Elk Creek channel will generate sufficient excess fill to provide a minimum offour feet of cover over the reclaim tunnel and associated demolition debris disposal area. A material balance for final backfilling and grading activities was developed based on comparison of the premining or existing and the postmining topography maps. The reclamation material balance resulted in a cut-fill isopach and material balance table that are included in Exhibit 2.05-E5, Reclamation Details. Generally, drainage and sediment control structures including diversion ditches for undisturbed area runoff, collection ditches for disturbed area runoff, sedimentation ponds, and localized drainage and sediment control features and Alternative Sediment Controls will either be retained during final reclamation or reconstructed or replaced by postmining drainage structures during final grading. These drainage and sediment control features will remain in place during the initial portion of the reclamation liability period and will be removed, unless previously approved as permanent structures. Removal and reclamation of associated disturbance areas will occur following DMG approval of Phase II Bond Release or the drainage restoration demonstration under Rule 4.05.2(2). Ditches will be reclaimed by reducing the ditch cross-sectional profile by grading ditch sideslopes into the ditch channel and blending the regraded sideslopes with adjacent areas. Smaller ditches may be reclaimed and eliminated through natural siltation. When these ditches are no longer needed to control drainage and sediment, C-1981-022,SL-1 Page 7 of 19