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• 4. Using SEDCAD, or other acceptable software, computer run to determine the <br />proper size of culvert to handle the peak runoff forma 10-year, 24 hour <br />precipitation event. Also check the pipe sizing using the hydrograph of <br />corrugated steel pipe culverts with inlet or outlet control, the discharge <br />quantity, and the amount of entrance head desired. <br />Other applicable methods of culvert design include the use of charts developed by the <br />Federal Highway Administration, published in Hydrologic Engineering Circular HEC-5 (FHA, <br />1980), and Hydrologic Design Series HDS-3 (FHA, 1980). <br />Charts published in HEC-10 (FHA, 1978) are also used; however, exit velocities must then <br />be determined by other methods. Headwater conditions are typically examined by using <br />HEC-5 inlet control nomograph. To be conservative and to allow for adequate freeboard, <br />WFC usually uses "projecting" conditions. <br />As virtually all culverts have free out falls, inlet control assumptions can be verified by the <br />"Pipe Flow Charts" in HDS-3. If flow in the culvert has a free surface, entrance control <br />exists, and exit velocity can be approximated by using the greater of normal or critical <br />• velocity determined by the "Pipe Flow Charts" in HDS-3. <br />Maintenance. Haul roads will be inspected on a daily work basis at the New Horizon Mine. <br />If, upon inspection, it is determined that repairs are needed, appropriate repairs such as, but <br />not limited to, grading, filling of potholes, replacement of the road surfaces, revegetation of <br />side slopes and watering for dust control, will be conducted as necessary. Magnesium <br />Chloride solution may be utilized to control fugitive dust. The solution will have an <br />approximate concentration of 30% and will be applied at a rate of one-half gallon per square <br />yard of surface area. The solution of Magnesium Chloride will be applied by a commercial <br />company specializing in this product and will be dispensed from a truck with approximate 16 <br />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 <br />CDMG approves such request, immediately after the road is no longer needed for <br />operations, reclamation, or monitoring: <br />a. The road will be closed to vehicular traffic; <br />. b. The natural-drainage patterns will be restored; <br />(Revised July 2006) 2.05.3(3)-31 <br />