2008-05-08_PERMIT FILE - C1981018A (3)

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• slope erosion, allow the reclaimed banks to blend into the existing natural terrain and allow animals to graze on the sides after final reclamation. Estimates of sediment from the first four refuse areas are included in Illustration 8. The results are listed below. These estimates are based on the entire refuse pile being covered with bare topsoil. The estimates were made using the (USLE) Universal Soil Loss Equation (see Section V.B.4), Since seeding will commence soon after the topsoil is placed, these estimates are conservatively higher than actually anticipated. As vegetation is established, the sediment yield per year will be drastically reduced. When vegetation has been established equal to the premining growth in the area, the sediment yield will be on the order of 25 times less than for bare soil as calculated. Sub-area Too of Pile Face of Pile 1 7.1 TPY 529.2 TPY 2-3 6.8 TPY 1,872.4 TPY 4 10.5 TPY 1,368.4 TPY The layout of the waste banks and a typical cross section are presented in Maps 76, 77, 77A, 63 and 150. The last lift will not be compacted and its top 8-12" will be scarified to enhance a permeable interface for roots and water. V.B.6 Post Reclamation Sediment Control Sediment Pond DP-1 which collects runoff from the • D Portal Area, will be removed during the removal of the Scullion Gulch diversion system when the D Portal Area is reclaimed. A series of three loose rock check dams have been constructed in the Scullion Gulch stream bed and its tributaries in the D Portal Area. The loose rock check dams ahd other sediment control measures are discussed in Section IV.J. The loose rock check dams are shown on Maps 43, 44 and 46. Cross-sections and details are shown on Map 43. The three loose rock check dams will be removed following successful reclamation and revegetation of the D-Portal area upstream. The loose rock check dams will retard streamflow and thereby minimize erosion in the reclaim@d Scullion Gulch stream bed. In addition, sediment deposition will occur behind the dams during runoff from small storms. It is anticipated that seepage through the rock dams will be partially blinded off by sediment deposition and thereby provide a minimal amount of settling volume for runoff from small storms. The total storage volume behind the three check dams is 1.74 acre-feet. The 3 year average sediment yield (per USLE) for the reclaimed D Portal Area is 0.51 acre-feet. The three year sediment yield for the total drainage area above and including the D Portal Area is 6.02 acre-feet, Thus, the reclaimed D Portal Area with the proposed contour furrowing and mulching would increase the sediment load in the Scullion Gulch at the D Portal Area by only 9.3% without the check dams being installed. See Illustration 22 for calculations. • Mid-Term Review 2002 (8/2002) V-14