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.. '- 'J ~' ~ fault sources in the vicinity of the proposed dam and evaluation of site response will still need to be resolved. construction Materials Several potential borrow areas near the dam site have been investigated by means of a power auger for impervious embankment sources. Large volumes of silty clay soil containing basalt cobbles and boulders are available. Separation will be necessary to remove the oversize rock fragments; however, the oversize rock can be utilized in the outer zones of the dam. Pervious materials are not plentiful in the area, but some pervious gravel could be processed from the channel area of Buzzard Creek. The volume of available materials is very small and washing will be required. There are no local sources of materials available for use and other sources of materials will be required., The nearest source of gravel suitable for concrete aggregate would be the Colorado River near Rifle, Colorado. This source would require a haul distance of about 40 miles. Some of the cobbles and boulders that will be available from screening in the impervious borrow areas would be suitable for riprap. Additional riprap will require a haul distance of approximately 8 miles from an igneous dike outcrop. Dam The potential Owens Creek Dam would be a rolled earth and rockfill structure with a maximum height of 165 feet above streambed. Its crest would be about 1,700 feet in length at elevation 8,315 feet with a width of 30 feet. Due to the lack of locally available sand and gravel or rockfill the embankment and the foundation are designed as a homogeneous clay dam with a chimney drain and drainage blanket. The entire area under the dam structure would require stripping of the top 12 inches of surface material before placement of dam embankment material. The amount of excavation outside of the cut-off trench could be greater than 12 inches depending upon the nature of the material. The depth of unsuitable materials is probably about 5 feet on the average. The Bureau of Reclamation has excavated an average depth of 8 feet from the foundation for the dam. A cutoff trench excavated in original ground would have its centerline parallel to and 100 feet upstream from the dam axis. Along the abutments the cut off trench will change direction to join the axis. The trench would have a bottom width of 100 feet with side slopes of 1/2:1 in overburden and 1:1/2 in rock. The trench will be excavated at least 10 feet into the Wasatch Formation to remove weathered, and fractured rock. The rock slakes rapidly upon exposure to air and protective coating will be used immediately after excavation. A 5