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The Division has approved the use of riprap channel lining for reconstructed channels in the <br />reclaimed area. Channel protection is warranted due to steep slopes and large watershed areas <br />that exist and that are planned on the post- mining topography. Pre - mining bedrock control of <br />erosion of natural channels is removed by the mining operation and channel protection is <br />necessary to provide long -term stability on the reclaimed area until vegetation is established. <br />The riprap lining will provide stability in order to protect fills and property and to avoid danger <br />to public health and safety (4.05.3(3)). Riprap used in many of Colowyo's channels to control <br />erosion ensures channel stability and requires infrequent maintenance (Rules 4.05.4(2)(a) and <br />(4.05.4(4)(b)). <br />Minor realignments and changes in permanent stream channel profiles are permitted within <br />reclaimed areas and excess spoil fill areas. Pre - mining and post- mining alignments are similar; <br />however, profiles deviate more markedly (Maps 33 and 33A) for both smaller drainages and <br />larger drainages. For larger drainages, the most significant example of altered profiles is Streeter <br />Gulch. Pre - mining, it was a steep- sided, 200 -foot deep incised draw near the mouth (PAP, Map <br />11). Initial box cut material for mining south of this gulch was placed near the mouth, first as an <br />experimental practice and later recognized as excess spoil (overburden) fill. As a result, <br />upstream topography was modified. The pre- mining profile ranged from 5 percent near the <br />lower end, increasing to 12.5 percent for the upper 1,800 feet (measurements from Map 18). The <br />post- mining profile is 30 percent for the first 1,000 feet up the face of the Streeter Spoil fill, and <br />approximately 4 percent across the approved post- mining topography of reclaimed land <br />(measurements from Map 19). <br />D. Sedimentation Control Measures, Ponds and Discharge Structures - Rules 4.05.5, 4.05.6, <br />and 4.05.7 <br />Channel linings, retention basins, and artificial channel roughness structures are approved for use <br />to control erosion. These practices increase channel stability and reduce the need for channel <br />maintenance. Riprap lining, sediment ponds, and dugout sediment traps on the spoil areas <br />(a.k.a., stocktanks) are the measures that are commonly used at the Mine. Channels with riprap <br />lining are discussed above. <br />Sediment ponds at Colowyo have been designed, constructed, and maintained to effectively trap <br />sediment from runoff resulting from precipitation events up to and including the 10 -year, 24- <br />hour precipitation event. Design criteria and specifications for sediment pond design and <br />construction are based on a thorough analytical demonstration by a qualified professional <br />engineer. None of Colowyo's sediment ponds are in a perennial stream (per Rule 4.05.6(1)(b)). <br />Twelve sediment ponds are in place to treat disturbed area surface water runoff. These are the <br />Streeter, Gulch A, Prospect, Gossard Loadout, Stoker Siding, Railway Loop, Work Area, West <br />Pit, East Taylor, West Taylor, Section 16, and Section 28 Ponds. The Section 21 Pond is <br />approved but has not yet been constructed; per Colowyo staff it is not likely this pond will be <br />Proposed Decision and Findings of Compliance January 2012 <br />Permit Renewal 06 Page 133 <br />