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A. GENERAL <br />The layout for the sediment collection ditches, watershed diversion and <br />the sediment pond is shown on Map 12, Mine Site Water Systems and Refuse <br />Area. <br />All diversions and sediment collection ditches which handle runoff from <br />an area above the refuse storage area and runoff directly off the refuse <br />pile, are designed to safely pass the 100-year, 24-hour storm event. <br />The disturbed runoff from the bench areas will collect at the lowest point <br />adjacent to the lower seam portals. At this point a sump will be <br />constructed to handle the runoff from the 10-year, 24-hour event. <br />The sediment pond is designed to provide storage for the maximum <br />anticipated inflow from a 10-year, 24-hour precipitation event, maximum <br />3-year sediment volume and mine water discharge from the No.lMinu and <br />.~ Storage mines. <br />The designs for Watershed Diversion Ditch A1, Watershed Diversion Ditch <br />N2 and the Refuse Sediment collection Ditches were determined utilizing <br />the SEDCAD+ computer model developed by Civil Software Design. The <br />designs for the sediment pond and all remaining ,diversions and ditches <br />are based on the reference: Procedures for Determining Peak Flows in <br />Colorado developed by the Soil Conservation Service. <br />Typical cross sections and design details for the sediment pond and the <br />Permanent Watershed Diversion are shown on Exhibit C, Sediment Pond and <br />Watershed Diversion Detail. <br />Design details and typical channel cross sections for diversion ditches <br />1 and 2, the refuse sediment collection ditches, and all remaining <br />collection ditches are contained in Figure A, Refuse Diversion and <br />Collection Ditch Design Details. Table A, Drainage Structure Design <br />Summary, illustrates the basis for design. <br />358 Rcvisecl 5193 <br />