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EXHIBIT 7, ITEM 20, PART D <br /> TEMPORARY CHANNEL DESIGN <br /> For the Section 28 sediment pond, two temporary ditches will be needed. These are the Section <br /> 28 and Section 29 Ditches as presented on Map 41 A. <br /> Design and construction of these ditches will be similar to the existing side channel ditches, <br /> which are currently in place at the Colowyo Mine. As shown on the Figure Exh. 7-20A-1, the <br /> runoff from the Section 29 collector ditch is contributory to the Section 28 ditch. Given the size <br /> of the drainage area involved for both ditches, the 10 year - 24 hour event as described by Rule <br /> 4.05.3 is the appropriate design basis. <br /> Both ditches are designed to be trapezoidal in cross section with a 12 foot bottom width and <br /> 2H:1 V sideslopes and a total depth of not less than 4.0 feet. As shown in the 10 year, 24 hour <br /> SEDCAD analysis in Exhibit 7, Item 20, Part A, no erosion protection is necessary for Section <br /> 28 and 29 Ditches, and the SEDCAD model confirms the trapezoidal design parameters <br /> presented here. <br /> Exh. 7-20D-1 Revision Date: 1/28/19 <br /> Revision No.: TR-131 <br />