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<br />' The buttress is stable with a 1.8 static factor of <br />safety. The buttress will be constructed of inter•burden waste <br />' rock material end dumped from the pit benches. The buttress <br />will be constructed in two lifts. As shown on Figure E.3.1-2, <br />' the lower lift will be end dumped and graded to a 3H:1V <br />outslope. The upper lift will be left at the angle of repose. <br />' The lower slope will be topsoiled with 18 inches of topsoil <br />material and revegetated with the approved seed mixture. Trees <br />' will be planted at a minimum rate of 100 trees per acre. <br />Stability of the buttress was analyzed using a simplified <br />' Janbu method. The buttress is stable with a 1.8 static factor <br />of safety. The buttress is estimated to be 600 ft long. Figure <br />' F-2 shows the approximate extent of the buttress <br />Final design for the buttress will be determined when <br />the exact characteristics of the geology and seE~page in the <br />south wall are known. The design will be finalized in the first <br />' two years of mining along the south wall and submitted to the <br />Division for approval. <br />' If seepage management operations indicate that there is <br />' a potential for large volumes of seepage which ma.y affect the <br />long-term stability of the rock buttress, a low permeability <br />' barrier such as a slurry wall or cutoff trer~ch will be <br />installed through the alluvium and keyed into the surrounding <br />Santa Fe Conglomerate. The typical design is shown on Figure <br />' E.3.1-2. Figure E.3.1-3 shows the estimated extent of the <br />slurry wall. Figures E.3.1-4 and E.3.1-5 show a Longitudinal <br />and transverse cross-section, respectively.The need for the <br />low permeability barrier will be evaluated during the first <br />' two years of mining in the south wall area. Final designs will <br />be submitted to the Division for approval. <br />1 <br />1 <br />' E-12 (Revised 4/20/89) <br />