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I I I I I I I I I I I I I I I I I I I Woodward.CIyde Consultants construction of a larger cutoff collar, and is most likely to minimize seepage around the outlet pipe. The alternative allows for the removal of anomalies or deleterious material that may exist within the present embankment in this area. The selected option for rehabilitation of Douglas Dam consists of removing the existing embankment above the outlet works as described above. A cutoff collar will also be constructed around the exposed outlet pipe upstream of the well tower. The excavation will be backfilled with the excavated material and additional embankment fill material needed would be from a proposed borrow area located northeast of the right abutment in the reservoir storage area. A chimney/blanket drain would be constructed downstream of the well tower. The reconstructed embankment will have downstream and upstream slopes of approximately 2.7:1. The completed embankment would have a crest width of approximately 20 feet. Riprap, underlain by a bedding layer, will be placed on the upstream slope. The downstream slope of the embankment will be seeded with native grasses. A soil-bentonite slurry wall will be constructed near the upstream toe of the , reconstructed embankment. The slurry wall will extend about 20 feet on either side of the outlet pipe. The slurry wall will be constructed around the intake to the outlet pipe and extend to the bedrock. 5.4.2 Outlet Works l~ In general, major improvements will not be made to the existing outlet works. A cutoff collar will be constructed upstream of the well tower following the excavation of the embankment. 5.4.3 Spillway Following the Colorado State Engineer Office Rules and Regulations for dams impounding water, ,the spillway of Douglas Dam should be able to safely pass 75% of the Probable Maximum Flood (PMP). Presently, Douglas Dam has two spillways: 22539G/DOUGLAS.DAM 12-J7-90/REPORTS3 25