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<br />• Alluvial soils are anticipated in a narrow band along the bottom of drainages <br />consisting primarily of clays with interbedded loose to medium dense sands to <br />depths on the order of 5 to 15 feet. Generally, stiff to very stiff clays are anticipated. <br />Medium stiff layers are considered likely but not predominant. Outside the drainage <br />ways, stiff to very stiff colluvial and residual clays are anticipated to shallow depths, <br />typically on the order of 1 to 3 feet, possibly as deep as 10 feet. Previous testing <br />of a bulk sample of colluvial/residual clay soil from the New Elk RDA Site indicated <br />a liquid limit of 37 percent, plasticity index of 16 percent, and 63% silt and clay sized <br />particles. This low plasticity, sandy clay is considered consistent with the geologic <br />conditions. <br />Tooopraahv <br />Topographic conditions in the disposal areas range from mild slopes of less <br />than 10 percent, to relatively steep slopes on the order of 50 percent. Average <br />• slopes along the axis of drainages within spoil areas range from about 8 to 27 <br />percent. The valley-like shape of most disposal areas will provide confinement of the <br />fills, enhancing stabilty. We believe the disposal areas are located in generally <br />favorable topographic conditions to achieve stability. <br />STABILITY ANALYSIS <br />The initial stability analysis consisted of developing typical sections which <br />represent topographic conditions at the 21 proposed disposal areas; estimating <br />soil/bedrock depths; research to estimate strength properties for the analysis and <br />consideration of ground water and earthquake effects. The following sections <br />describe each of these steps along with the results. Tables and figures related to <br />the stability analysis are presented in Appendix A. <br />The analysis sections used were biased towards worst case topography, and <br />conditions at many fills will be more favorable. The strength parameters selected are <br />• considered to be conservative. The relatively low slopes proposed for the spoil fills <br />LORENOITO COAL COMPANY <br />cTUr zs,zsi 6 <br />