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low bluffs of the Pierre formation. The maximum height will be about 165 feet above the Pierre formation beneath the South Platte River. The embankment on the right side of the river will extend southwestward about 16000 feet or about 3 miles. The embankment height gradually tapers to a very thin wedge as the ground surface rises from the river to the gently rolling plains to the south. . 3.4.2 The core will be extended by a 100-foot wide cutoff trench to the Pierre formation on the left abutment and continuing 1500 feet on the right abutment. It connects to a slurry trench cutoff to the south. It is planned to be supported on the stripped virgin soils upstream and down- stream of the cutoff trench. 3.4.3 The core will be plastic clay obtained from thin flood plain blanket on the left or north side of the river just upstream of the dam. The core will be 360 feet wide at the base, more than twice the head and about 20 feet at the top. 3.4.4 A sloping chimney drain transition filter will be placed between the downstream shell and the core below elevation 4430 (slightly above the flood control pool) . This will connect with a continuous blanket drain beneath the downstream shell. 3.4.5 The core will be supported by sand and gravel shells with variable outer slopes from the top down of 2.5(H) to l(V), 3(H) to l(V) and 4(R) to l(V) upstream, and 2(H) to l(V), 2.5(H) to l(V), and 3(H) to l(V) downstream. . 3.4.6 A deep slurry trench cutoff extended from the core to the Pierre will be provided on the southwest or right abutment. It begins near the river where the Pierre becomes so deep that an excavated cutoff becomes impractical. The preliminary length is 4500 feet. It ends arbitrarily where the ground surface is elevation 4400, about the top of the conservation pool. . 3.4.7 Southwest of the slurry trench cutoff, a founda- tion relief drain system is contemplated. The preliminary design indicates that this will consist of deep drain wells to relieve excess pore pressures in the deepening gravelly alluvium southwest of the slurry trench cutoff. 5