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across the approved post-mining topography of reclaimed land (measurements from Map 19 of the <br /> 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 to <br /> 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 /> stock tanks)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 100-year, 24- hour <br /> precipitation event. Design criteria and specifications for sediment pond design and construction are <br /> 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 /> Twenty sediment ponds are permitted to treat disturbed area surface water runoff at the Mine. These <br /> are the Prospect, Gossard Loadout, Stoker Siding, Railway Loop, Work Area, West Pit, East Taylor, <br /> West Taylor, Upper Section 3, Lower Section 3, Section 15, Section 16, Section 28, Section 25, <br /> Section 26, Section 36, Middle, Sidehill, Coal Stockpile, and Temporary Facilities Ponds. Designs <br /> for these ponds are included in Exhibit 7 and the locations of the ponds are shown on Maps 12, 12A, <br /> 2313, 13C-1,41 and 41A of the PAP. <br /> Sediment ponds and stock tanks at the Mine have been determined to be environmentally sound and <br /> structurally stable (Rule 4.05.6(11)). <br /> E.Acid forming and Toxic forming 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. Results <br /> from past sampling are included in the Annual Reclamation Reports associated with the Mine. <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 /> Design, construction, and maintenance of impoundments at the Mine meet the requirements of <br /> 33 <br /> Permit Revision No.5(PR-05),G 1981-019 <br />