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-3- <br /> <br />The results of our stability analysis, summarized on Fig. 2, indicates that <br />the fill will be stable as planned with 2 horizontal to 1 vertical out- <br />slopes. A factor of safety of 2.3 was calculated fora deep circular <br />failure surface which extended to the pit spoil. The factor of safety <br />increases significantly if the failure surface passes partially through the <br />bedrock. The factor of safety is also relatively high (1.7) for surfaces <br />which pass almost entirely through the compacted spoil. The factor of safety <br />is about 1.5 for shallow, infinite type failures of the slope face at a <br />2:1 ratio. <br />Recommendations <br />1. In our opinion, the selected site can safely be developed as <br />a temporary spoil disposal area. <br />2. Prior to the placement of fill, all vegetation, topsoil and <br />organic matter must be removed. <br />3. Spoil should be placed in approximately horizontal layers, about <br />4 feet in thickness and be compacted. We believe that compaction <br />of the fill is necessary to achieve desired strengths. The fill <br />should be placed in a manner similar to that used during construc- <br />tion of Excess Spoil Disposal Areas I and II in Eckman Park. <br />4. Our analyses indicates a factor of safety of 1.5 using outslopes <br />no steeper than 2 horizontal to 1 vertical. We recommend fill <br />slopes be no steeper than 2:1. <br />5. Based upon our interpretation of "Regulations of the Colorado <br />Mine Land Reclamation Board for Coal Mining" (MLRB), we believe <br />that construction of diversion ditches will be necessary around <br />the fill. We suggest that diversions be designed and constructed <br />for at least a 10-year precipitation event. <br />The recommendations and conclusions presented in this letter are based upon <br />previous investigations we have conducted in the general vicinity of the <br />proposed temporary spoil storage area and our interpretation of the require- <br />ments of the Colorado MLRB. If we can be of further service in discussing <br />the contents of this letter, or construction of the disposal area from a <br />geotechnical paint of view, please call. __ <br />Ver trul ours, ; Pr :~•:: o~if=~ <br />Y Y Y -~ ~ .• <br />CTL/TH MP ON I C / ~ •' y;~ <br />r • _- <br />By i iam C.. ffman Jr. , P.E. •a~ Q t <br />Reviewed by ~~ ~ ~ •'a~- <br />,L ~, <br />Robert W. Thompsa~r;~P.E. President ~ ==~~ <br />WCH:RWT:dm <br />(7 copies sent) <br />3cc: Colorado Yampa Coal Co., P.O. Box 772129 <br />Steamboat Springs, Colo 80477 Att: Mr. Michael W. Ludlow <br />