1996-06-04_REVISION - M1977493 (9)

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Continuing from the second vault to Tenmile Pond, the pipeline will drop down the west groin of No. 2 Dam and discharge into a short riprap lined channel that leads to the water pool. As an alternative, it may be less expensive to replace the discharge channel with a short length of additional pipe that would be placed on the ground surface and extend to the water pool. The end of the pipe could then be cut off as the water level in the pool increases. Continuing from the second vault to Robinson Pond, the pipeline will increase from 20-inch to 24-inch diameter to minimize the friction losses along the crest of No. 2 Dam. This portion of the pipeline will also be nearly level, although it is possible to maintain the negative slope required to allow the pipe to drain. The 24-inch pipeline will discharge into a riprap lined channel that would extend to the water pool on the tailing pond. A small concrete headwall would be constructed at the pipeline discharge point. Alternate pipeline routes were considered and rejected for various reasons. However, one alternative which warrants possible further consideration is the installation of the new pipeline inside of the Tenmile Tunnel, which passes directly under the valve vault at the west end of No. 2 Dam. The pipeline route proposed herein closely parallels the alignment of the Tenmile Tunnel. A bore hole into the tunnel (similar to the Riser 6 bore) would be required near the location of the valve vault to convey the water into Robinson or Tenmile Tailing Ponds. Several advantages to this alternative are as follows: 1) a more favorable pipeline profile for surge protection, 2) the elimination of the long length of pipe that would be placed across the tailing pond, 3) an additional discharge option would be available whereby the pumped flow could be delivered through the tunnel bulkhead directly to the toe of No. 3 Dam via the Tenmile Tunnel Extension. 19