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drainage ditches will be maintained periodically to prevent accumulation of debris on the • <br />culverts inlets and outlets. <br />The general design procedures used in the design of cul•+e its is contained in Attachment <br />13-1. <br />Tables 13-5 and 13-6 contain an inventory of existing and proposed culverts at the Seneca <br />II-W Mine. All existing culverts are adequate. Figure 13-3 and Figure 13-4 show typical <br />installation of culverts. Other applicable methods include the use of charts de•+eloped by <br />the Federal Highway Administration, published in Hydr of ogic Engineering Circular HEC-5 <br />(FHA, 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 nomography, To be conservative and to allow for adequate freeboard, <br />Peabody usually uses "projecting" conditions. <br />As virtually all culverts have free outfalls, inlet control assumptions can be verified by • <br />the "Pipe Flow Charts" in HDS-3. If flow in the culvert has a free surface, entrance <br />control exists, and exit velocity can be approximated by using the greater of normal or <br />critical velocity determined by the "Pipe Flaw Charts" in HDS-3. <br />Maintenance. Access roads will be inspected on a daily work basis at the Seneca II-W <br />Mine. If, upon inspection, it is determined that repairs are needed, appropriate repairs <br />such as, but not limited to, blading, filling of potholes, replacement of the road <br />surfaces, revegetation of side slopes and watering for dust control, will be conducted as <br />necessary. <br />Restoration. Unless Peabody requests retention of access roads for po stmining land use <br />and the Division 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 />c. All bridges and culverts will be removed; <br />d. Roadbeds will be ripped, plowed and scarified; • <br />e. Fill slopes will be rounded or reduced and shaped to conform the site to <br />34 <br /> <br />