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across the approved post-mining topography of reclaimed land (measurements from Map 19 of <br /> the PAP). <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 commonly used at the Mine. <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 /> 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 <br /> the ponds are constructed and two, the Section 26 and the Sidehill Ponds, are in the process of <br /> being constructed as of the date of these Findings. Designs for these ponds are included in <br /> Exhibit 7 and the locations of the ponds are shown on Maps 12, 12A, 2313, 13C-1, 41 and 41A of <br /> the PAP. <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. Acidforming and Toxicforming Spoil - Rule 4.05.8 <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. <br /> Results from past sampling are included in the Annual Reclamation Reports associated with the <br /> Mine. <br /> No evidence of toxic effects to vegetation on reclaimed areas has been reported to date on the <br /> mine site. <br /> F. Impoundments - Rule 4.05.9 <br /> Design, construction, and maintenance of impoundments at the Mine meet the requirements of <br /> Proposed Decision and Findings of Compliance January 5,2023 <br /> Permit Renewal No. 8 Page 137 <br />