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<br />The D50 for spoil material in the area is approximately 0.18, <br />therefore, riprap with a D50 of 6 inches or less will not <br />require a filter blanket since the graded spoil will serve the <br />same purpose. For channels requiring riprap with a D50 greater <br />than 6 inches, SCC will use geotextile material as a filter <br />blanket. The designs have been revised accordingly. <br />18. The designs are intended to give SCC some flexibility in the <br />field. As the channels are constructed, the channels will be <br />surveyed to determine a representative slope range. Based on <br />channel slope, an appropriate lining will be selected and <br />placed. For estimating where channel lining will be required, <br />design slopes for the proposed channels are shown on the <br />channel profiles and the slopes requiring riprap are indicated <br />on the associated table. <br />19. As indicated on the culvert table in Appendix 7-12, Appendix <br />C, Culvert Designs, the HW~D for Culverts 3A and 18A is 1.5 <br />and 1.7, respectively. This would indicate corresponding <br />headwater depths of 3.8 feet and 3.4 feet, respectively. The <br />Division used 3 feet and 2.4 feet, respectively. If the <br />Division uses the headwater depths indicated on the table, the <br />SEDCAD+ results show the existing culverts to be adequate. <br />20. SCC has removed the stocktanks from Exhibit 7-19 for the time <br />• being. Once a review of these existing features is completed, <br />SCC will submit a separate revision that will incorporate <br />these structures into the postmining drainage control plan and <br />meet the requirements of Rule 4.05.9 for permanent <br />impoundments. <br />21. Exhibit, 7-20, sheet 14 of 23, SIIPM-14 Channel Profile, has <br />been revised to correct the error detected by the Division. <br />• <br />