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<br />Proposed Decision and Findings of Compliance July 2018 <br />Permit Renewal No. 7 P a g e | 33 <br />with discharges from underground workings will not occur at these sites. <br /> <br />B. Diversions and Conveyance of Overland Flow - Rule 4.05.3 <br /> <br />The drainage and sediment control plan provides for temporary and permanent diversion of <br />surface drainages within the permit area. A system of ditches, as shown on Maps 11 and 12 as <br />well as Exhibit 7 of the PAP, convey runoff through disturbed areas and divert runoff from <br />disturbed areas to sediment ponds. <br /> <br />C. Stream Channel Diversions and Reconstruction - Rule 4.05.4 <br /> <br />Diversions of perennial streams around mined areas is not a regular practice at the Mine. <br /> <br />Reconstruction of channels is an important aspect of Colowyo’s reclamation practices. <br />Reconstructed channels are designed (and certified by a registered professional engineer) to <br />accommodate the 100-year design storm event (Rule 4.05.4(2)(a) and (b)). The channels are <br />designed not to increase flooding or otherwise endanger property or public safety and are designed <br />to be stable and not adversely impact the hydrologic balance. Reconstructed channels at the Mine <br />have not been designed with a lesser flow capacity than the unmodified stream channel <br />immediately above and below the diversion (Rule 4.05.4(2)(b)). These channels are shown on <br />Maps 41, 41A, and 41B of the PAP. <br /> <br />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 is necessary to provide <br />long-term stability on the reclaimed area until vegetation is established. The riprap lining will <br />provide stability in order to protect fills and property and to avoid danger to public health and <br />safety (4.05.3(3)). Riprap used in Colowyo’s channels to control erosion ensures channel stability <br />and requires infrequent maintenance (Rules 4.05.4(2)(a) and (4.05.4(4)(b)). <br /> <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, 33A, 33B and 33C of the PAP) for both <br />smaller drainages and larger drainages. For larger drainages, the most significant example of <br />altered profiles is Streeter Gulch. Pre-mining, Streeter Gulch steep-sided with a 200-foot incised <br />draw near the mouth of the gulch (PAP, Map 11). Initial box cut material for mining south of this <br />gulch was placed near the mouth, first as an experimental practice and later recognized as excess <br />spoil (overburden) fill. As a result, upstream topography was modified. The pre-mining profile <br />ranged from 5 percent near the lower end and increasing to 12.5 percent for the upper 1,800 feet <br />(measurements from Map 18 of the PAP). The post-mining profile is 30 percent for the first 1,000 <br />feet up the face of the Streeter Spoil fill and approximately 4 percent across the approved post- <br />mining topography of reclaimed land (measurements from Map 19 of the PAP). <br />D. Sedimentation Control Measures, Ponds and Discharge Structures - Rules 4.05.5, 4.05.6,