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GRAND JUNCTION • LINCOLN DeVORE, Inc. GEOTECHNIC41. ENGINEERS -GEOLOGISTS ISaI Motor St. TEL. (970)?a?-ft96S Grand Junction, CO 81505 FAX: (970j '_a?-1561 December 16, 1999 Steve Self 1098 County Road 214 Silt, CO 81652 Re: The Sediment Pond, SPI, Fast Side Mine, Silt, CO Slope stability calculations were performed on the existing embankment, using cross section and soils information provided to Grand ]unction Lincoln DeVore by the client. The stability analysis addressed the individual slope and the `global' condition of the entire embankment. The analysis was performed using the PC software SLOPE/W, Version 4, Geo-Slope International LTD, Calgary, Alberta, Canada. The analysis utilized the Limit Equilibrium Theory for the factor of safety, incorporating 4 methods. Fellemius or Ordinary Method = Moment Equilibrium Bishop Simplified Method = Moment Equilibrium Janbu Simplified Method = Force Equilibrium Morgenstern-Price Method = Moment and Force Equilibrium • No seismic coefficient was assumed in these calculations. Several models were assumed for the existing embanlanent. The critical models assumed the ground water level within the embankment has stabilized consistent with a `fiill' reservoir. The water storage in a `full' condition is critical for the Face Failure Model. For the Pond Face failure model, the reservoir contains no sediment and the embankment is saturated, following `rapid drawdown' of the reservoirs fluid. The soils information regarding in-place soil density (not known if saturate, moist or dry) and soils data (not known if ultimate or residual strength) on soils only described as fill and foundation soils were provided in sheets taken from a Lambert & Associates report. These two sheets, which were `faxed' to Grand Junction Lincoln DeVore on 12-6-99 are designated Figure 5 & 6, project # M85021 GB, 3-14-85 and designated W edge Failure Analysis at the Fill/Natural Contact and Stability Analysis for Tce Failure. The analysis indicated the embanlatlent configuration provided to Grand Junction Lincoln DeVore has a sufficient factor of safety, greater than 1.3, assuming the in-place embankment section and geotechnical data are consistent with the calculated model. For the face failure mode, the critical failure surface was obtained using the Janbu method, with a calculated factor of 4.29. The face failure model with the full reservoir critical surface was obtained using the Janbu method and produced a safety factor of 5.88. The face failure model incorporating a'rapid downdown' situation, with no sediment in the pond was also found to be critical using the Janbu method of analysis, producing a safety factor of 3.63. Considering the embanlmlent is only 8 %: feet high, these values are reasonable. Included with this letter report is a figure indicating the 3 critical calculations in a reduced fom7at on a single sheet. The next 12 figures represent the critical failure calculations for the critical models, as calculated by . the 4 methods.