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drainage ditches will be maintained periodically to prevent accumulation of debris on the culverts inlets • <br />and outlets. <br />The general design procedures used in the design of culverts is contained in Attachment 13-1. <br />Tables 13-5 and 13-6 contain an inventory of existing and proposed culverts at the Seneca II-W Mine. <br />All existing culverts are adequate. Figure 13-3 and Figure 13-4 show typical installation of culverts. <br />Other applicable methods include the use of charts developed by the Federal Highway Administration, <br />published in Hydrologic Engineering Circular HEC-5 (FHA, 19801, and Hydrologic Design Series HDS-3 <br />(FHA, 19801. Charts published in HEC-10 (FHA, 1978) are also used; however, exit velocities must <br />then be determined~by other methods. Headwater conditions are typically examined by using HEC-5 <br />inlet control Homographs. To be conservative and to allow for adequate freeboard, Peabody usually <br />uses "projecting" conditions. <br />As virtually all culverts have free outfalls, inlet control assumptions can be verified by the "Pipe Flow <br />Charts" in HDS-3. If flow in the culvert has a free surface, entrance control exists, and exit velocity <br />can be approximated by using the greater of normal or critical velocity determined by the "Pipe Flow <br />Charts" in HDS-3. <br />Maintenance. Access roads will be inspected on a daily work basis at the Seneca II-W Mine. If, upon • <br />inspection, it is determined that repairs are needed, appropriate repairs such as, but not limited to, <br />blading, fitling of potholes, replacement of the road surfaces, revegetation of side slopes and watering <br />for dust control, will be conducted as necessary. <br />Restoration. Unless SCC requests retention of access roads for postmining land use and the Division <br />approves such request, immediately after the road is no longer needed for operations, reclamation, or <br />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 />l J <br />34 <br />