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11 r. Tew .-I~Mvn O.~'bvrr .1 fim~ GmPan) Oi/ I'/00 PgrJ • Phreadc Surfue A range of phreatic surface elevations in the brnch fills were assumed for the analyse. The phreatic surface within the bench fills was assumed to rise up to a maximum of 14 Feet into the fills. The mtical height (Factor of Safety (FS) drops below 1.3) of the phreatic surface in the bench fills tins de[errrtined to be between 12 and 13 feet A plot of phreatic surface rise in the fills versus FS is presrnted in Attachment B. It is not antiapated that surface or ground water would sanuate or infiltrate laterally or vertically into the bench fills, so phrntic surface use should remain well below critical levels. The phrntic surface in the soil stockpile was assumed to intersect the ground surface at the top of the st«kpile where surface wa[u diversion ditches will ditett flow off of the st«kpile. The groundwatu surface wu assumed to use no higher than 10 feet below the czisting ground surface at the base of the soil pile. No springs or seeps exist on the slope where the soil stockpile will be located. Thuefore, the phreatic surface u not expected to rise above the costing grotmd surface after placemrnt of the soil pile. .~ phreatic surface was projected for the pond D embankmrnt based on Casagrande's procedure for seepage through homogeneous embankmrnts (193 and an upstream water level equal to the elevation of the emergrncy spillway. This elevation u conservative because the watu level should not be maintained above the principal spilhvay invert elevation long enough to produce the coaesponding use in the phreatic surface. This calculation is included in Attachment B. Stability Analyeia The computer program SLOPE/W was used to espmate factors of safety for the proposed sections of the brnch fills and soil stocl~ile. Bishop's method of slice was used in conjunction with a seuch routine to estimate the lowest possible factor of safety for the given input conditions. Three diEEerrnt slope stability scenaaos were evaluated: • Brnch Fills (2H:1~; • Pond D Embankmrnt; and • Soil Stockpile (2H:11~ The I«ations of the cross-sections for the brnch fills and the topsoil stockpile are shoam on Figure 1. Both aoss-sections were developed to portray the marimum slope height and slope angle for the bench fills and soil stockpile. The two aoss-section geometaa with a geologic descuption of the rnateuaLs are presented u Figures 2 and 3. The pond Daoss-section is shown on the Pond D Design Drawing (Drawing 205-MSG) of the Ozboa Mining, Inc., Mining and Reclamation Plw Permit document The SLOPE/W rams and results ue provided in Attachment B, Skpe Srabr6q Calnrlatieu. Stability Aaalyaie Results Based on the input parameters discussed previously and the attached sections, the results of the stability calculations for the bench fills and sod st«kpde for static conditions were u follows: ' • Brnch FiIL+ Sutic Factor oESafety (Phrntic surface 0 feet into (ill): 1.48 .`