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0 <br />• ~ SUMMARY OF CONCLUSIONS <br />1. The preliminary stability analysis consisted of developing typical <br />sections which represent topographic conditions at the 21 proposed <br />disposal areas; estimating soil/bedrock depths and strength <br />properties and consideration of ground water and earthquake effects. <br />2. The analysis sections used were biased towards worst case <br />topography, and conditions at many fills will be more favorable. The <br />strength parameters selected are considered to be conservative. The <br />relatively low slopes proposed for the spoil fills of 3:1 (H:V) would be <br />expected to result in favorable stability conditions unless very poor <br />foundation materials are present or water developed in the fill. This is <br />confirmed by the analysis. <br />3. The stability analysis indicates stable fill meeting CDMG requirements <br />should be possible at the locations and configurations planned. Static <br />analysis shows adequate factors of safety (>1.5) for the normal <br />strengths evaluated. Low friction angles in the native soils (less than <br />15 degrees) are not anticipated, but the strength properties of the clay <br />should be evaluated during site specific investigations. Buildup of <br />water in the fills results in potential slumping near the toe, indicating <br />• drainage is required. Pseudo-static analysis indicates satisfactory <br />conditions (F.S > 1.3). Site specific investigations should be <br />performed for each disposal area to identify localized hazards (slumps, <br />slides or seeps); and to confirm soil/ground water conditions, <br />strength properties and topographic conditions. <br />4. After specific investigations for several fills in various conditions are <br />completed, we believe it should be possible to extrapolate spoil and <br />soil engineering properties using classification testing. <br />Reconnaissance and subsurface investigation at each disposal area, <br />by a qualified engineer familiar with site conditions and the <br />assumptions used in the stability analysis will be required. The scope <br />of investigation and design should evolve as investigations are <br />completed. <br />BASIS FOR EVALUATION <br />Our understanding of fill configurations and proposed construction <br />procedures is based upon discussions with Greystone. Documents provided by <br />Greystone for our review included: <br />• <br />LOFiENCITO COAL COMPANY <br />CM 25,251 2 <br />