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May 6, 1987 <br /> <br />Water, Waste & Land, Inc. <br />CONSULTING ENGINEERS 8 SCIENTISTS <br />Wyoming Fuei Company <br />12055 W. Second Place <br />P. 0. Box 15596 <br />Lakewood, Colorado 80215 <br />Attention: Mr. Steve Magnuson, Mining Engineer <br />Subject: New Etk Mine <br />Refuse Pile Stability <br />Dear Mr. Magnuson: <br />This letter documents the methods and <br />Elk Mine coal processing waste pile. <br />1987, the results indicate that minir <br />MLRD criteria under anticipated pore <br />This analysis was conducted according <br />31, 1987. <br />waste. , <br />~~ <br />_;;381077 ;T.;,.=, <br />''V1> <br />'mil <br />^,r '~i <br />~r = <br />~~ <br />RF <br />,~~ ~~ ~~ <br />#2142 <br />results of stability analyses of the New <br />As discussed by telephone on April 20, <br />aum factors of safety are above Colorado <br />water pressure conditions in the pile. <br />to your request 1n a letter dated March <br />Stability analyses were previously conducted for the New Elk Mine coal <br />processing waste pile in 1984, based upon typical materiai properties from U.S. <br />Bureau of.. Mines data (WWL, 1984). This letter presents an update of these <br />analyses based upon geotechnical testing of the New Elk Mine coal processing <br />WASTE PILE DESCRIPTION <br />From information provided by Wyoming Fuel Company, the waste pile has been <br />constructed according to Colorado MLRD requirements for coal processing waste, <br />including placement in two foot thick lifts and compaction to approximately 90 <br />percent of Standard Proctor density (for the material). <br />The pile has been constructed along the side of the Purgatoire River Valley, <br />underlain by sedimentary rocks. The final height of the pile (from the top of <br />the pile to the toe) will be approximately 500 feet. Overall outside slopes of <br />the pile will vary as shown by the typical section shown in Figure 1. <br />GEOTECHNICAL TE57ING <br />• Geotechnical tests were conducted on a representative sample of the coal <br />processing waste (or refuse) collected by Wyoming Fuel Company. Tests <br />consisted of one Standard Proctor test (ASTM D-698, Method C) with sieve <br />