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-9- <br />• <br />borrow area south of Energy Fuels office, the clay has an <br />optimum moisture content of 15 and a maximum dry density of 112 <br />pcf. This material contains about 15 percent sand sizes. The <br />clay from within the reservoir areas was more plastic, had about <br />11 percent sand sizes, and had an optimum moisture content of 20.8 <br />with a maximum dry density of 101 pcf. Both of these soils when <br />compacted will have permeabilities of less than 1 foot per year. <br />Laboratory shear tests were made on remolded samples of the clay <br />borrow materials. Results of these tests are presented on Fig• <br />18. <br />DAM FOUNDATION <br />• Borings near the axis of [he proposed embankment indicate the thick- <br />ness of the overburden soils ranges from 7 to approximately 18 feet. If <br />underseepage is to be completely controlled, we believe it will be neces- <br />sary to provide a cutoff trench extending into the bedrock surface. The <br />dam can be safely constructed with a partial cutoff. 7n order to <br />allow construction, it will be necessary to provide temporary dewater- <br />ing during construction. We anticipate that the dewatering could be <br />accomplished by excavating a sump and pumping from within the excavation. <br />The construction schedule can be accelerated by excavating a drainage <br />trench along the valley bottom to a point downstream from the anticipated <br />embankment construction. At that point, a relatively deep sump pit can <br />be excavated and pumping can be used to accelerate the rate of water re- <br />moval prior to attempting excavation of a cutoff trench. This will also <br />• improve conditions during the stripping operation. We recommend removing <br />