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SENT 81~~Xerox 7elecopier 7020 ;1~2-93 829 303675~9~ 303 986 8147.# 4 <br />DEC-ZI-9E TUE 14:23 LiHC DEVORE GJ E0324~e61 r.o~ <br />• <br />Western Fuels - Utah <br />Coal Wast• Pile Stability <br />Deeerado Mine, Rangely, CO <br />Dscembar 20, 1993 page 9 <br />The Critical failure surfaces of the Ultimate strength analysis <br />'.~ extended through the Waste Plle and into the native, Poundation <br />~ soils. The failure surfaces were found to be influenced by the <br />',presence of the PP-5A Pond. It wee determined the PP-SA Pond <br />1.hould ^ither be sealed to prevent saturation oY the Pile toe <br />foundation soils or the pond should be moved to approximately 160 <br />feet away from the toe oY the Waste Pile. Even if moved, the <br />ground surface of the PP-5A Pond should be properly oompocted, <br />utilising clayey soils, to reduce the possibility of saturation <br />of the toe foundation soils, An analysis of the Geology, possible <br />subsurface roster flow within the foundation soils and apeoific <br />recommendations for construction of the Wnete Pile and the PP-6A <br />Pond is not a part of this study. <br />The Shear Strength perimeters of the coal waste material should <br />be confirmed by sampling and testing on a periodic basis during <br />the waste Dile construction to assure that weaker sores are not <br />• incorporated into the construction. It ie anticipated that <br />stratification of the pile will occur during construction, which <br />may result 1n perched water tables within the refuge pile. It is <br />recommended the refuge Dile be constructed with a Blight crown <br />during the placement of individual lifts. The purpose of this <br />alight crowning is to aide in the removal of surface moisture <br />which may accumulate during construction. <br />It ie reoommended density testa be perforDied on a regular basis <br />to verify that the final compaction densities are being achieved <br />by the conetl•uction teehniquee. If the coal refuge charaeterie- <br />tics ohattge during construction or if soil, rock or ground water <br />conditions differ fro those for which the analysis was per- <br />formed, this office eh~uld be advised that re-evaluation can be <br />made, if necessary. <br />I <br />It le believed that all pertinent point^ have been addressed. It <br />any further questions arise regarding this project or St we can <br />be of any further asaifitance, please do not hesitate to contact <br />this office at any time. <br />Respectfully submitted, <br />LINCOLN DeVORE, Inc. <br />.~ <br />• by: Edward M. Morris EIT Reviewed by: Oeorge D. Morrie, PE <br />Engineer/Western Slope Hanager <br />LD Job No.:80073-J <br />