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4.0 DESIGN ASPECTS The following sections detail site-specific aspects of the construction of the proposed coal mine waste bank and ancillary facilities at the Sanborn Creek Mine. The proposed waste bank was designed to optimize the available space and accommodate maximum coal mine waste quantities, while incurring minimal disturbance to the surrounding landscape. Calculations for the height -volume relationship of the waste bank are included in Appendix C. 4.1 CONSTRUCTION 4.1.1 General Construction of the proposed coal mine waste bank begins with the sediment pond, sediment pond access road, and upland diversion ditch. A plan view of the waste bank is shown on Drawing 95255-01. The sediment pond is designed to collect storm water runoff and the associated sediment transported with it. Discussion of the sediment pond requirements is presented in Section 4.2 of this document. Upland diversion will be constructed on an existing road above the proposed waste bank, as shown on the drawings. Diversion ditches are discussed in detail in Section 4.1.4 of this document. The toe was sited to begin at a relatively flat area at Elevation (EI.) 6,050 feet (ft) in the center of the draw. This area should be stripped of topsoil and stockpiled in the Elk Creek topsoil stockpile and used later as part of the reclamation process. Generally, during typical wastebank construction topsoil should be removed in small quantities ahead of the developing waste bank to control erosion potential of the stripped, unvegetated subsurface and placed directly on exposed coal mine waste that is ready for reclamation. Initially, stripping should proceed within the waste bank foot print to EI. 6,100 ft. It is recommended that 4 terraces be constructed to approximately 10 feet wide within this initial stripping area. These terraces will aide in providing stability for the waste bank. These terraces should be placed at elevations shown on Drawing 95255-02, at ten-foot elevation increments. Terrace details are shown on Drawing 95255-03. An underdrain system should be started during initial construction which will discharge flow into the sediment pond. The underdrain system is discussed in detail in Section 4.1.2. The proper placement of the first coal mine waste lifts is critical to overall stability of the waste • bank. Compaction of the material should be a minimum of 90 percent of the maximum dry 96256/1424.FPT Coal Mine Weete eenk Design for the Sanborn Creek Mina October 1996 WESTEC, Inc. 6