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<br />• the fill area. Some surface water will flow to the fill area from the limited area <br />remaining. Movement of fill from above will limit the locations where temporary <br />diversion, ditches for surtace water can be constructed. We do not believe complete <br />diversion of surface water will be required. Temporary diversion ditches should be <br />used as much as practical, particularly for large area fills (such as Fills 14 and 17). <br />The temporary diversion ditches can be planned for inactive areas as construction <br />processes evolve for each fill. <br />Keywavs <br />Large keyways or rock toe buttresses are not required based on the <br />preliminary stability models. However, it is likely that shallow soil deposits in the <br />drainageways will be lower strength and some removal of this material will be <br />required. Atypical keyway cut is shown on Fig. 4. <br />For valley-like fills, we believe keyway cuts should be provided at the toe, <br />• extending from the drainage way to both sides until shallow bedrock or very stiff <br />soils are found. The conceptual extent of the keyway is shown on Figs. 3 and 4. For <br />narrow valleys with little soil cover the depth and extent will be nominal. For wider <br />valley openings we anticipate depths on the order of 4 to 6 feet and widths of 8 to <br />12 feet. Removal of soft or loose soils may be required behind the keyway (50 to <br />100 feet behind the toe) within the lower portions of the drainage. <br />If the drain exit will be above the keyway cut, water accumulation in the <br />keyway could occur. For this conditions we do not recommend filling the keyway <br />with spoil fill. It would be preferrable to have the base of the drain pass across the <br />bottom of the keyway, exit the toe and then be provided with a gravity outlet. If this <br />is not feasible then the keyway can be filled with compacted natural sands or clays <br />or with durable sandstone rock fill meeting drain rock requirements. Sand or clay <br />fill should be compacted to at least 90 percent of maximum modified Proctor dry <br />density (ASTM D 1557) within 2 percent of optimum moisture content. <br /> <br />LORENOITO COAL COMPANY <br />cTLrr zs,ssi 12 <br />