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I I I I I I I I I I I I I I I I I I I information based on work done at the Juniata Reservoir can be made. The primary formation is probably the Mancos Shale formation and is within 10 to 15 feet of the surface. The Mancos Shale is potentially weak in shear and is slightly expansive, with a bearing capacity in the range of 10,000 to 20,000 psf. Although there would not appear to be a major problem with construction of a dam founded on the Mancos Shale, a geotechnical investigation of the properties of the material would be necessary during final design of the dam. The sideslopes and top width used in this study should provide an adequate factor of safety for stability in the Mancos Shale. The Mancos Shale is covered by alluvium material. The alluvium is highly variable in particle size, ranging from 30" basalt boulders to clay particles. This type of materi a 1 generally has a hi gher hori zonta 1 permeabil ity than vert i ca 1 permeability, a high variation in settlement characteristics along a cross section of the material and material scattered throughout it. It appears this materi a 1 coul d be effecti ve ly sealed against seepage by a cut off trench thru the alluvium and keyed into the competant primary formation. The potential problem of differential settlement along the axis would need to be evaluated during detailed design. Alternative 1 utilized the existing dam in the upstream face of the new dam. The suitabi 1 ity of us i ng the exi sti ng dam as part of the embankment for the new dam depends on several factors i nc 1 udi ng: compaction of the embankment materials; internal drainage; outlet works; stability of the dam; and seepage contro 1 measures. These items can be eva 1 uated by cori ng and testi ng the embankment material, review of existing historical records, and a field investigation. The final decision on whether to utilize the existing dam in 4-4