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A. GENERAL <br />• The layouts for the sediment collection ditches, watershed diversions, and the sediment pond <br />are shown on Map 12, Mine Site Water Systems and Refuse Area. <br />All diversions and sediment collection ditches which handle runoff from the area above the <br />refuse storage area or runoff directly off the refuse pile are designed to safely pazs the 104year, <br />24hour storm event. <br />The disturbed runoff from pottal bench areas will collect at the lowest point adjacent to the <br />lower seam portals. At [his point, a sump will be cons[ructed to handle the runoff from the <br />10-year, 24hour event. <br />The sediment pond is designed to provide storage for the maximum anticipated inflow from a <br />10-year, 24hour precipitation event, maximum 1-year sediment volume. <br />The designs for the Sediment Pond Watershed Diversion Ditches Nl through NS and the Refuse <br />Sediment Collection Ditches were developed utilizing the SEDCAD+ computer model <br />developed by Civil Software Design. The designs for the permanent diversion and Nlvett are <br />based on the reference: °Procedures for Determining Peak Flows in Colorado" developed by <br />the USDA Soil Conservation Service. <br />Typical cross-sections and design details for the Sediment Pond design details are presented in <br />Exhibit N, Sediment Pond Design Map. Table A, Drainage Structure Design Summary, <br />illustrates the basis for design of these structures. <br />C~ <br /> <br />A:~B56ATRI7REV 358R Revised -June 1993 <br />avov9~ zp~ . <br />