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Ir. Thann~ Aurlerran, P.E. <br />sbou~ dlirrivy Lrt. <br />:1 /,q, ?c. 1999 <br />P,rge ? <br />a.0 POND STABILITY EVALUATION AND RESULTS <br />The stability assessment was completed using a basic, ono-dimensional equilibrium analysis program called <br />XSTABL (v5.2), assuming a circular failure mode and calculating the static Safety Factor (SF) using the <br />Bishop method. Fur the stability analysis, a typical embankment cross-section reflecting the existine pond <br />configuration as' shown on Drawing I, Pond E Stability Cross-Section, was used. A water surface elevatton <br />behind the embankmem of 6126.5 feet above mean sea level (amsl), corresponding to the im-ert elevation <br />of the pond spillway, was assumed. Similarly, the potential phreatic surf:ice for the stability analysis was <br />based on the spilhvay invert elevation of 6126.5 ft-amyl. The phreatic surface through the embankment <br />was estimated based on Darcy's law and Casagrandc's procedure as outlined by Huang (1983). The <br />resulting surface is shown on Figure I, Pond E Stability Cross-Section. <br />Soil properties for the pond foundation and embankment were developed from the soil description supplied <br />by Oxbow and the attached Figure 7 from the Navel Facilities Engineering Command Design Manuel 7.01. <br />Soil Mechanics. As shown on Figure 7, given a soil classification of SM at a dry density of 100 psf <br />(relative density 6590) gives an angle of internal friction of 33 degrees. For this assessment we <br />conservatively assumed no cohesion. <br />Using the described inputs, the stability analysis indicates a static SF of 1.4 which is greater than the SF of <br />1.3 required under applicable provisions of Rule 4.05.6(1 l)(k). The attached XSTABL computer printotns <br />document all inputs and stability analysis results. If you have any questions or require additional <br />information regarding this pond stability evaluation please do not hesitate to contact me. <br />Respectfully, <br />Montgomery Watson Mining Group \``\\\\\`~P00 I REGIS ~~i,~ <br />_~ ..., ~ I <br />OHO ~ S E <F~~ ~~9~, <br />.°F? c~ e o <br />• 3459 ~' - <br />Thomas E. Leidich P.E. ~ A b ~ <br />Senior Engineer ~~~ o~ ,+'\~~\ <br />Attachments ~; yi4y~`r~pNgl t~~6\``~~ <br />cc: toe Dudash/DMG ~ic~. <br />Jerry Nettle[on/MW ' <br />File <br />TEL/ech <br />os/zc/9r <br />