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I I I I I I I I I I I I I I I I I I I r (.. ,U, ~ L li..) '..;.. -3- natural ground and is about 2,000 feet wide. The complete c~toff was believed necessary by the U.S.B.R. because of the possibility of high seepage flows endangering the stability of the downstreaa slope of the dam. The design also includes a wide, iapervious core and a large open-pit excavation to bedrock except in the buried channel area. Both of these require hauling and placement of major quantities of impervious clays.from the pits previously located about 7 miles upstream. This material is relativ~ly ) expensive. Also, the Bureau design contemplates use of sand-gravel cobbles from the main stream bottom and these materials are also relatively expensive to excavate and place. In our opinion, a complete cutoff to bedrock is necessary for safety of the dam embankment except in the deep buried channel. We believe that the materials overlying the buried channel are sufficiently laminated and are sufficiently iapervious that leakage through the buried channel will not endanger the daa. Also, a daa with a complete cutoff such as envisioned by the U.S.B.R. would not be equivalent to the dam at the Narrows site where it is impossible to have a complete cutoff. At the Narrows site the whole right side of the reservoir abuts the horizontally laminated overburden sands and gravels and, we believe, will be much more susceptible to reservoir seepage and danger of instability than the Weld County site. We believe that the central impervious zone should be much thinner and that the foundation excavation should be much smaller thus making more use of the locally available materials and less use of the impervious clays which have to be hauled a great ~"C"'.A"j~~l~1 ..r.,..",:,..,.[lt.S~U I~'I'