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• 1. Identify the need for a structure from topographic (naps, and a visit to the site; <br />2. Determine the size and hydrology of the watershed in question; <br />3. Perform SEDCAD, or other acceptable software, computer run to determine the <br />peak runoff from a 10-year, 24-hour precipitation event. <br />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 quantity, <br />and the amount of entrance head 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 <br />inlet control nomograph. To be conservative and to allow for adequate freeboard, WFC usually <br />uses "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 normal or critical velocity determined by <br />the "Pipe Flow Charts" in HDS-3. <br />Maintenance. Haul roads will be inspected on a daily work basis at the New Horizon Mine. If, <br />upon inspection, it is determined that repairs are needed, appropriate repairs such as, but not <br />limited to, grading, filling of potholes, replacement of the road surfaces, revegetation of side <br />slopes and watering for dust control, will be conducted as necessary. Magnesium Chloride <br />solution may be utilized to control fugitive dust. The solution will have an approximate <br />concentration of 30% and will be applied at a rate of one-half gallon per square yard of surface <br />area. The solution of Magnesium Chloride will be applied by a commercial company <br />specializing in this product and will be dispensed from a truck with approximate 16 foot spray <br />bars. One-two applications are anticipated per year. <br />• <br />(REVISED 12/00) 2.05.3(3) -16 <br />