2007-06-29_PERMIT FILE - C1981022A (2)

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Sewn - 2.05.4 Final backfiring and grading will be completed to create a stable final topography appropriate to the postrtrinurg land use. The final topographic configuration of the Elk Creek Facilities area is shown by the Facilities Postrnining Topography Map, (Maps 2.05-M6), and the Postntining Goss-Sections, (Map 2.05-M7). The backfiring and regrading plan for this area is based on the following objectives and constraints: • Backfilling will be limited to those areaz where fill is necessary to stabilize exposed highwall areas, provide sufficient cover over demolition debris, or achieve effettive drainage. Fill material will be placed and cornpacted by equipment traffic to approximately 80 percent of maximum dry density. • Final grading plans are designed to establish slope gradients consistent with upgradient natural slopes but not exceeding 2II:1V. Final grading will be conducted, to the extent operationally feasible, along the contour to mi~imi>P subsequent erosion and instability. Final grading will elinunate anylarge depressions that could impound water. • ILgltwall areas will be backfilled and graded to blend with adjacent undisturbed slopes and reclaimed areas. The Somerset Mine B and C Seam portak were sealed and backfilled in 1986 and associated face-up areaz have already been backfilled and graded. Final grading activities for the Elk Creek Facilities area will not redisturb these regraded areas. • Because the source of the material used to construct the Elk Creek Mme portal bench was a natural landslide above the portal area, all of the bench material cannot be utilized in establishment of the design postmirting topography for the Elk Creek Mme facilities area and it cannot be replaced in its original location in a stable configuration. For this reazon, approximately 72,000 cubic yards of bench material will be hauled down-valley from the Elk Creek Mme facilities area and placed in the Elk Creek surface facilities area az supplemental fill. Inclusion of this supplemental fill a reflected in the design posttnining topography and cross-sections. Portions of existing bench areas tray be retained, if compatible with the postmining topography and reclamation objettives, to control runoff and direct surface flows to reestablished drainages. Where portions of benches are retained, bench crests will be rounded and the resulting cut material will be pushed downslope to reduce overall outslope gradients. Bench ouulopes will generally be less than 50 feet in length, so contour furrows or other runoff control meazures will aot be necessary. The combination of short slope lengths and limited drainage areas will result in stable slopes when revegetated. The Elk Creek culvert will be removed, except for two short sectioru to be retained or replaced for the Sanborn Creek and Elk Creek roads. The culvert will be excavated, removed, and hauled off-site for disposal. Following culvert removal, the corresponding segmenu of the Elk Creek channel will be reconstructed. Channel reconstruction will involve grading to establish the design postmining channel configuration as illustrated by the Elk Creek Profiles, (Map 2.05-M7), and the Postmining Topography Map and Goss-Sectioru, (Maps 2.05-M6 and 2.05-M7), placement of riprap materials, az required; replacement of available soil material on the upper channel slopes; and revegetation of both channel and sideslope areas. The recotutmtted Elk Creek channel has been designed to safely pass the peak flows resulting from a 100-yz'az, 24-hour storm event. The designed channel haz 2FL1V sideslopes, a 10- to 12-foot bottom • width, and overall gradients consistent with both the original channel and the existing culvert. Qrarrtrel 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 m~n~mi>r channel erosion. Riprap placement will extend approximately 3 to 4 fee[ up the channel PR04 2.05-57 Revised August 2000