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4. Using SEDCAD, or other acceptable software, computer run to determine the proper <br />• size of culvert to handle the peak runoff forma 10-year, 24 hour precipitation event. <br />Also check the pipe sizing using the hydrograph of corrugated steel pipe culverts <br />with inlet or outlet control, the discharge quantity, and the amount of entrance head <br />desired. <br />Other applicable methods of culvert design include the use of charts developed by the Federal <br />Highway Administration, published in Hydrologic Engineering Circular HEC-5 (FHA, 1980), and <br />Hydrologic Design Series HDS-3 (FHA, 1980). <br />Charts published in HEC-10 (FHA, 1978) are also used; however, exit velocities must then be <br />determined by other methods. Headwater conditions are typically examined by using HEC-5 inlet <br />control nomograph. To be conservative and to allow for adequate freeboard, WFC usually uses <br />"projecting" conditions. <br />As virtually all culverts have free out falls, inlet control assumptions can be verified by the "Pipe <br />Flow Charts" in HDS-3. If flow in the culvert has a free surface, entrance control exists, and exit <br />velocity can be approximated by using the greater of norrnal or critical velocity determined by the <br />• "Pipe Flow Charts:'. i~ HDS-3. <br />Maintenance. Haul roads will be inspected on a daily work basis at the New Horizon Mine. If, upon <br />inspection, it is determined that repairs are needed, appropriate repairs such as, but not limited to, <br />grading, filling of potholes, replacement of the road surfaces, revegetation of side slopes and <br />watering for dust control, will be conducted as necessary. Magnesium Chloride solution may be <br />utilized to control fugitive dust. The solution will have an approximate concentration of 30% and will <br />be applied at a rate of one-half gallon per square yard of surface area. The solution of Magnesium <br />Chloride will be applied by a commercial company specializing in this product and will be dispensed <br />from a truck with approximate 16 foot spray bars. One-two applications are anticipated per year. <br />Restoration. Unless WFC requests retention of haul roads for postmining land use and the CDMG <br />approves such request, immediately after the road is no longer needed for operations, reclamation, <br />or monitoring: <br />a. The road will be closed to vehicular traffic; <br />• (Reviaea ~/zooaJ 2.05.3(3) - 26 <br />