Condit Dam Removal Condit Dam Removal - Access Washington

Condit Dam Hydroelectric Project
Final Supplemental EIS
• PacifiCorp would use BMPs during the construction, dam removal, and restoration
activities at the project site, thus minimizing the potential for spills and other releases
of hazardous substances.
• Because a portion of the equipment fueling would take place where surface water
could be impacted by a spill or release (such as fueling of the demolition crane
situated on the dam spillway), prevention and management of spills, such as through
temporary containment, would be practiced.
Additional mitigation measures are not recommended.
Dam Breaching and Removal
Drain Tunnel
• Water used in drilling into the dam to develop the drain tunnel would be collected and
removed from the site.
• Large blocks of concrete would be removed from the stream. Downstream from the
powerhouse, pH would be monitored continuously and compared with background
levels.
• Blasting would be accomplished in accordance with the Blasting Plan (PacifiCorp
2004).
• Implementation of the plans developed by PacifiCorp should minimize the impacts
related to the drain tunnel, and no additional mitigation measures are recommended.
• 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 its lower end of the 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 should 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
The instream work associated with this diversion has the potential to suspend sediments in the
river, thus increasing turbidity.
• 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
should include mitigation measures to minimize impacts to surface water quality and
should consider alternative replacement options. This plan would need to include an
application for a change in the point of diversion.
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