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Client Memorandum <br />Geotechnical and Slope Stability Analyses <br />Sylvester Gulch Facilities Area <br />• March 20, 2009 <br />Page 7 <br />These slope stability analyses indicate that the Second Pond excavation and constructed <br />embankment slopes should provide for long-term stability, if constructed in accordance with <br />specified designs and construction quality assurance controls. <br />Consolidation Analyses <br />Consolidation analyses were performed for the maximum embankment section height based on <br />the laboratory one-dimensional consolidation analyses for site soil samples. Using an <br />embankment unit weight of 118 pcf and the maximum height of 10 feet, estimated consolidation <br />of the subsurface is approximately 0.2 to 0.4 inches. This consolidation would likely occur <br />during or shortly after construction. Additional long-term secondary settlements are expected to <br />be less than 2.6 inches. <br />Therefore, significant settlement should not be a concern for the Second Pond. However, to <br />monitor stability performance of the Second Pond, it is recommended that two settlement <br />monuments be installed in the embankment crest, one at the northeast corner and one along the <br />east side of the embankment in the southern portion of the facility. <br />C. <br />REFERENCES <br />Lambert & Associates, 2008. Laboratory Test Results and Test Hole Logs, West Elk Mine, <br />Letter to Ryan Sweetwood, December 24. <br />Lambert & Associates, 2009. Sieve Analysis, Atterberg Limits; Sample No. 1358 Laboratory <br />Test Results, West Elk Mine, Letter to Ryan Sweetwood, February 20. <br />RocScience, Inc. 2009. Two-Dimensional Equilibrium Slope Stability Analysis Model Slide <br />5.0, Toronto, Ontario. <br />U.S. Bureau of Reclamation (USBR), 1987. Design of Small Dams, U.S. Government Printing <br />Office, Washington, D.C. <br />U. S. Department of the Navy (USDN), 1971. Soil Mechanics, Foundations and Earth Structures, <br />Design Manual, Navfac DM-7 <br />U. S. Department of the Navy (USDN), 1982. Soil Mechanics Design Manual 7, Naval Facilities <br />Engineering Command, Alexandria, VA. <br />• U.S. Geological Survey, 2002. Western U.S. Seismic Maps, Peak Acceleration (%g) with 10% <br />Probability of Exceedance in 50 Years, October 2002. <br />Rev. 04109-TR116