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fill slopes ac the Edna Mine, the Bishop's simplified method of slices was <br />• used. The theory, procedure and tables used to calculate the factor of safety <br />was taken from Rock Slime Enq~'n,'~na, Chapter 9: "Circular Failure," Revised <br />Third Edition, written by E. Hoek and J.W. Bray. In using this information to <br />calculate the factor of safety, a number of parameters and some assumptions <br />are made. This information was complied using reference material, actual mine <br />site conditions and estimations based on prudent engineering judgment. In all <br />cases, a conservative approach was used to determine the minimum factor of <br />safety. To calculate the factor of safety, cross sections were prepared for <br />existirq roadways ac the Edna Mine whose roadway cut and fill slopes exceeded <br />the maximum regulatory slope limits. A representative "worst case" example of <br />road fill slope and a road cut slope were chosen from these cross sections and <br />used to perform a slope stability analysis. The road fill, having an <br />embankment slope of 1v:1.7h, was found to have a factor of safety of F (factor <br />• <br />r <br />~J <br />of safety) = 5.6. The road cut slope, having a slope of 1v;1.4h, was found to <br />have a factor of safety or F = 2.9. The procedure and calculations for <br />determining the factor of safety is found in Appendix 3.5-B. <br />3.5.3 CULVERT DESIGN SUMMARY <br />Culverts were designed to carry the runoff from a 10-year, 24-hour storm <br />event. Runoff volume was generated by computer simulation based upon the SCS <br />rainfall-runoff prediction method. After peak flows were generated, culverts <br />were appropriately sized to carry the runoff with zero head. Locations of <br />culverts can be found on Exhibit 3.5-22. <br />3.5.3.'_ Culvert Drainage Areas for the Moffat Area <br />All culverts within the Moffat Area will be placed within the mining area <br />disturbed limits. Since mining will progress across all natural drainages, <br />culvert locations will be established during the regrading phase as mining <br />progresses. During the first several years of mining most of the drainage <br />from the regraded areas w'll flow along the roadways towards the active pit. <br />The flow will proceed along the pit floor to the low point along the western <br />edge of the active pit and be pumped into the collector ditches which will <br />3.5-3 May 14,1993 <br />