Condit Dam Removal Condit Dam Removal - Access Washington

Condit Dam Hydroelectric Project
Final Supplemental EIS
Impacts
• Deposition of sediment in the in-lieu site could potentially raise flood
elevations near the mouth of the White Salmon River until the sediment is
flushed out.
Table 1-1 (Continued)
Summary of Impacts and Mitigation Measures
Water Resources (Continued)
Mitigation
• Potential changes in the floodplain downstream of the dam, although they
appear to be small, could be minimized if the dam breaching were to occur
at a time when the Bonneville pool elevation is near the lower end of its
range of fluctuation. Breaching the dam during a time when the
Bonneville pool is low would reduce the flood elevations at the in-lieu
site. PacifiCorp would consult with the U.S. Army Corps of Engineers to
determine the feasibility of lowering the Bonneville pool prior to dam
breaching, in the event that the pool elevation is near the higher end of its
range of fluctuation.
Reconstruction of Mt. Adams Orchard Diversion
Reconstruction of Mt. Adams Orchard Diversion
• Replacing the irrigation diversion will have impacts • Instream sediment management during the diversion construction should
be similar to in-stream mitigation measures for the reinforcement of
Northwestern Lake Bridge (e.g., use of silt curtains).
• As the specific plans for the diversion construction are developed, the
scope of work would include mitigation measures to minimize impacts to
surface water quality.
• A well could substitute for withdrawal from the river and eliminate those
impacts. Wells are generally considered preferable to surface water
withdrawals. Since a change in the point of diversion would be required, a
well would be strongly considered and used if permits can be secured in
time.
Post-Removal Management
• The potential for water quality effects will extend past the initial activities
planned for dam removal and sediment stabilization.
Post-Removal Management
• To assess the effectiveness of the Sediment Management and Revegetation
Plans (PacifiCorp 2004), long-term water quality monitoring is proposed.
• Monitoring of applicable water quality parameters, including turbidity,
total suspended solids, and pH, as well as observation and documentation
of banks and fish passage, will continue from a month before the
commencement of dam removal activities until such time that performance
criteria are met (PacifiCorp 2004). In addition, PacifiCorp would conduct
turbidity monitoring in the Bonneville pool for 4 weeks after the dam is
breached and conduct turbidity monitoring at three locations in the White
Salmon River for a period of 10 years after the dam is breached.
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