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<br />Proposed Decision and Findings of Compliance July 2018 <br />Permit Renewal No. 7 P a g e | 34 <br />and 4.05.7 <br /> <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 (a.k.a., <br />stocktanks) are commonly used at the Mine. <br /> <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-hour <br />precipitation event. Design criteria and specifications for sediment pond design and construction <br />are based on a thorough analytical demonstration by a qualified professional engineer. None of <br />Colowyo’s sediment ponds are in a perennial stream (per Rule 4.05.6(1)(b)). <br /> <br />Nineteen sediment ponds are permitted to treat disturbed area surface water runoff at the Mine. <br />These are the Streeter, Gulch A, Prospect, Gossard Loadout, Stoker Siding, Railway Loop, Work <br />Area, West Pit, East Taylor, West Taylor, Section 16, Section 28, Section 25, Section 26, Section <br />36, Middle, Sidehill, Coal Stockpile, and Temporary Facilities Ponds. Currently, seventeen of the <br />ponds are constructed and two, the Section 26 and the Sidehill Ponds, are in the process of being <br />constructed as of the date of these Findings. Designs for these ponds are included in Exhibit 7 and <br />the locations of the ponds are shown on Maps 12, 12A, 23B, 13C-1, 41 and 41A of the PAP. <br /> <br />Sediment ponds and stocktanks at the Mine have been determined to be environmentally sound <br />and structurally stable (Rule 4.05.6(11)). <br />E. Acid-forming and Toxic-forming Spoil - Rule 4.05.8 <br /> <br />No significant acid-forming spoil exists within the overburden or coal seams to be mined (PAP, <br />Section 2.05.4). This determination has been supported with ongoing soil sampling, including <br />drilling in the South Taylor Pit and Collom Pit areas. Overburden sampling and regraded spoil <br />sampling plans are discussed in Section 2.05 of the PAP and Exhibit 6, Item 4 of the PAP. Results <br />from past sampling are included in the Annual Reclamation Reports associated with the Mine. <br /> <br />No evidence of toxic effects to vegetation on reclaimed areas has been reported to date on the mine <br />site. <br />F. Impoundments - Rule 4.05.9 <br /> <br />Design, construction, and maintenance of impoundments at the Mine meet the requirements of <br />Rule 4.05.9. These include: <br /> <br /> Sediment ponds (see discussion above) <br /> Stock ponds for watering of cattle and wildlife (see Exhibit 7, Item 15 of the PAP) <br /> Water treatment basins <br /> The Taylor Pump Holding Pond (which existed prior to August 3, 1977)