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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />If this test is representative of the morainal material, the foundation can <br /> <br />be expected to be dense and impervious. A test pit excavated in the valley <br /> <br />floor immediately upstream of the dam axis on August 23 indicated lakebed <br /> <br />sediment at the ground surface, as noted in the geologic report. The extent <br /> <br />of this material was not well defined but it would appear to provide an imper- <br /> <br />vious blanket of fine-grained soil overlying the more granular foundation <br /> <br />material. <br /> <br />Permeability. The above described gradation data and inspection infor- <br /> <br />mation available for this review indicate relatively impervious materials. <br /> <br />Considering the geologic history of the area, it would be expected that <br /> <br />stream channels backfilled with more pervious materials may be encountered <br /> <br />during foundation excavation. One such channel is suggested by the seepage <br /> <br />test data for TP-l, a hand-dug hole apparently excavated in 1936 near the <br /> <br />dam axis at the base of the right abutment. Based upon the reported pump-in <br /> <br />rate of 12 gpm, a coefficient of permeability of approximately 2,000 feet per <br /> <br />year was calculated by IECO. Continuous channels of such materials could <br /> <br />result in undesirable seepage rates if not cut off by the core trench. How- <br /> <br />ever, the water loss due to foundation seepage through a 20-foot deep channel, <br /> <br />100 feet wide, was calculated to be only about 0.1 cubic feet per second or <br /> <br />45 gallons per minute. Recommendations in this regard follow in Section II C. <br /> <br />C. Embankment Design <br />General. The fill materials proposed for use in the embankment are con- <br /> <br />sidered excellent in quality. In general, the dam is designed to utilize <br /> <br />these materials to best advantage.. However, considering the complexity of <br /> <br />the damsite and particularly the abutments, several minor design modifications <br /> <br />are recommended along the abutment contacts. The intent is to improve pro- <br /> <br />tection against piping or internal erosion of abutment materials due to <br /> <br />seepage gradients which will develop when the reservoir is raised and lowered, <br />