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RULE 4 PERFORMANCE STANDARDS <br />effectiveness of sediment control structures to be constructed around several topsoil stockpiles planned <br />outside of primary sediment control i nay be found under Exhibit 7, Item 23, Part D. <br />4.05.4 Stream Channel Diversions (Relocation of Streams) <br />The drainage and sediment control measures described under Section 2.05.6 and presented in the Erosion <br />and Sedimentation Control Plan (Exhibit 7, Item 23) and Exhibit 7, Item 25 —Collom Post Mine Channel <br />Design will provide for diversion or relocation of three ephemeral surface drainages within the permit <br />area. No perennial streams will be diverted for the proposed project. Stream channel diversions will be <br />constructed to pass at a minimum the runoff from the 100 -year, 24-hour precipitation event. <br />The diversions will be constructed with a minimum gradient to pass the design flow and will be stabilized <br />with grasses or riprap. If not removed by mining, upon completion of mining and at an appropriate point <br />mandated in the Coal Regulations of the Colorado Mined Land Reclamation Board, the stream channel <br />diversions will be reclaimed as required in Section 4.05.17. <br />The only stream channel that will be impacted by the Collom Lite pit is the main stream of Little Collom <br />Gulch, an ephemeral stream draining less than one square mile at the proposed upstream pit boundary. It <br />will not be diverted at the upstream boundary due to the small upstream drainage area, low runoff <br />production potential, and the impracticality and land disturbance associated with constructing a diversion <br />along steep canyon slopes. It will be channelized further downstream, alongside the haul road leading <br />from the Collom Lite pit to the proposed spoil pile, where it drains greater than one square mile. This <br />section will be subject to a 100 -year design. <br />The eastern lobe of the Little Collom X pit will intersect two small tributaries of Little Collom Gulch, <br />which collectively drain approximately one square mile. These tributaries will be diverted around the pit <br />in a ditch designed for the 100 -year event. <br />Two small ephemeral tributary gullies located east of the proposed spoil pile will also be affected by <br />operations. They will not be diverted, and will instead flow into gravity sorted material under the <br />proposed spoil pile. <br />The drainage and sediment control measures described under Section 2.05.6 and presented in the Erosion <br />and Sedimentation Control Plan (Exhibit 7, Item 23, Part E) and Map 41B will provide for temporary <br />diversion of surface drainages within the permit area, as needed for mine operations. A system of <br />temporary ditches will be used to divert runoff from disturbed areas to sediment ponds. The natural <br />drainage systems will be restored to historic drainage patterns once diversion ditches are removed; <br />therefore, there will be no permanent diversions of these channels. <br />4.05.5 Sediment Control Measures <br />Sediment control measures to be implemented are shown in the Erosion and Sedimentation Control Plan <br />(Exhibit 7, Item 23 in addition to Items 25-26). These facilities, consisting primarily of diversion ditches <br />and sedimentation ponds, will be located, constructed and maintained to avoid erosion and increased <br />contribution of sediment load to runoff. <br />Facilities to control sediment are t;,pically installed in areas above and/or below the planned sites of <br />disturbance. "Upstream" facilities, s ich as temporary diversion ditches and check dams upslope from the <br />mining activities, serve to divert runoff away from the disturbed areas. Because the Collom Lite mining <br />activities extend nearly to the top o` the erainages, no upstream facilities are proposed for Collom Lite. <br />Collom — Rule 4, Page 6 Revision Date: 9/28/11 <br />Revision No.: PR -03 <br />