2013-02-25_PERMIT FILE - C1982057A (6)

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Drainage from haul roads within the areas disturbed by mining and reclamation activities (see Exhibit 13-2) will be constructed to meet the requirements of Rule 4.05.2 and such haul roads will at a minimum be constructed and maintained to minimize erosion of the disturbed area. Erosion control measures to be used singly or in combination include but are not limited to: a. Stabilizing all exposed surface areas to promote a reduction in the rate and volume of runoff; b. Using straw dikes, dprap, check dams, berms, geotextile materials, mulches, vegetation sediment filters, contour furrows or other measures that reduce overland flow velocity, reduce runoff volume, or trap sediment; or c. Such other measures to minimize erosion resultant siltation and disturbance to the prevailing hydrological balance. Surfacinc. See Exhibit 13-10 for typical detail. Culverts. Each haul road will be designed, constructed, and maintained to have adequate drainage using ditches and culverts to safely convey the peak runoff from a 10-year, 24-hour precipitation event to sediment ponds before being released from the permitted area (see Exhibit 13-2 for general locations and Exhibit 13-10 for typical details of road drainage structures). Culverts will be installed to avoid plugging or collapse and to avoid erosion at the inlets and outlets. Riprap will be installed as necessary to reduce the exit velocity. The minimum width will be the width of the natural downstream channel. The riprap will be sized in the field by SCC's project engineer based on the "as-built" slope of the culvert and final configuration of the exit channel slope area. The sizing shall be based on the Federal Highway Administration's HEC No. 11 "Use of Riprap for Bank Protection" or other standard methods. All culverts will have a minimum cover of 12 inches. Culverts and drainage ditches will be maintained periodically to prevent accumulation of debris on the culverts inlets and outlets. The general design procedures used in the design of culverts is contained in Attachment 13-1 The SEDCAD culvert sub-routine was used to design the Seneca II-W culverts. Attachment 13-7, Culvert Calculations, presents the culvert designs. Tables 13-5, Summary of Culvert Design Characteristics for the Mine Area, and 13-6, Summary of Culvert Design Characteristics for the Tie-Across Haul Road, identify the culverts at the Seneca II-W Mine. All existing culverts are adequate. Figure 13-3, Typical In-Wash Culvert, and Figure 13-4, Typical Cross-Drain Culvert, show typical installation of culverts. Other applicable methods include the use of charts developed by the Federal Highway Administration, published in Hydrologic Engineedng Circular HEC-5 (FHA, 1980), and Hydrologic Design Series HDS-3 (FHA, 1980). Charts published in HEC-10 (FHA, 1978) were also used; however, exit velocities must then be determined by other methods. Headwater conditions are typically examined by using HEC-5 inlet control Homographs. To be conservative and to allow for adequate freeboard, SCC usually uses "projecting" conditions. PR-05 22