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0 <br /> <br />SCOPE <br />This report presents the results of our Stability Evaluation for eight existing <br />sedimentation pond embankments at the Kennecott Energy, Colowyo Coal Company <br />LP mine site in Moffat County, Colorado. We understand Colowyo has proposed a <br />technical revision which involves perforating existing risers. The use of perforated <br />risers instead of manually operated gate valves could increase the height of water <br />retained behind the embankments. Our evaluation is intended to satisfy Rule <br />4.05.9(5)(b) of the state regulations which require a minimum static safety factor of <br />1.3 for a normal pool with steady state seepage saturation conditions. <br />Our evaluation consisted of a review of construction documentation, visual <br />observations of each sediment pond, a review of our previous investigations at the <br />site, and a computer aided stability analysis. <br />• SUMMARY <br />A stability analysis was performed for eight existing sedimentation pond <br />embankments. Using conservative assumptions regarding geometry, water <br />conditions and strength parameters, the lowest factor of safety calculated was 2.0 <br />for steady state seepage saturation conditions. This exceeds the minimum <br />regulatory requirement of 1.3. <br />EMBANKMENT CONDITIONS <br />The eight embankments included in this evaluation are identified on Table I. <br />The table presents embankment characteristics including elevations, embankment <br />heights, water storage heights, slopes and other pertinent properties of the <br />embankments. The table was derived from information provided by Colowyo and <br />also our review of as-built construction plans. The as-built plans were dated April <br />1998 and are the same proposed plans submitted to Division of Minerals of Geology <br />COLOWYO COAL COMPANY, LP <br />STABILITY EVALUATION -SEDIMENTATION PONDS <br />CTLR 2B,t31 <br />