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Page 4of10 <br />16. Coal Mine Waste is achieving the required minimum level of compaction, but the <br />moisture content of the material is well above optimum, and above the level that has <br />been recommended by the geotechnical consultant. This elevated moisture content, <br />combined with the required level of compaction, may be contributing to the extended <br />amount of time required for the dissipation of excess pore pressure. <br />17. In order to counteract the excess moisture that is present in the waste that is generated <br />from the coal preparation plant, dry, native soil /colluvium ( "coverfill ") is routinely <br />blended with the coal mine waste. This mixture is evaluated for density and moisture <br />content during the regular compaction testing, but it does not appear that strength <br />properties, such as cohesion and angle of internal friction have been determined for <br />input into the stability analyses. Please reevaluate the stability of Gob Pile #2, <br />considering the material strength properties under the current practice of blending fill <br />material with refuse. <br />18. Unconsolidated - Undrained tests were conducted on samples of coal mine waste <br />collected in 2005 and 2006. No additional UU tests have been done since. Three <br />Consolidated - Undrained tests were performed on coal mine waste collected in 2005. If <br />(see item 13, above) there is a need to reincorporate Undrained conditions into <br />stability analyses, then updated UU and CU tests need to be performed on coal mine <br />waste blended with coverfill material. <br />If you have any questions or need additional information, please contact me. <br />Sincerely, <br />Susan L. Burgmaier <br />Environmental Protection Specialist <br />cc: Tamme Bishop, J.E. Stover & Associates <br />Marcia Talvitie, DRMS <br />