Condit Dam Removal Condit Dam Removal - Access Washington

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Condit Dam Hydroelectric Project Final Supplemental EIS revegetation of the reservoir area and other areas disturbed by construction activities (PacifiCorp 2004). • Fill placed in support of temporary roads on reservoir sediments will be removed once roads are no longer needed, and erosion stabilization will be used for all roads, storage areas, or construction staging areas. • Compliance monitoring will be independent from construction activities. At the end of the proposed action, all work sites will be regraded and revegetated to stop erosion and the release of fine sediments into the White Salmon River associated with these activities. • The spill prevention and spill clean-up plans will be used to prevent or minimize impacts to fish from spills and leaks of fuel and hazardous chemicals. Northwestern Lake • Silt curtains will be used during sheet pile installation to minimize silt entrainment in the water, or construction will be performed as the water level is lowered. In either case, silt entering the water column will be minimized (PacifiCorp 2004). Any work near the river will use erosion control mats and silt fencing to protect the river and aquatic fauna from sediment release. • Hazardous chemicals and fuel would be stored in secured storage areas with secondary containment. Spill prevention and spill containment plans would be in place for the contingency of a spill occurring or chemical contaminants reaching the lake or river. Dam Breaching and Removal Drain Tunnel • Water used for drilling into the dam to develop the drain tunnel will be collected and removed from the site. • Concrete rubble from construction of the tunnel will be captured and prevented from entering the river. After dam breaching, any blocks of concrete that get in the stream will be removed. Downstream from the powerhouse, pH will be monitored continuously and compared with background levels. • Blasting will be accomplished in accordance with the Blasting Plan (PacifiCorp 2004). A temporary weir below the dam site or cofferdam could prevent upstream migrating winter and summer steelhead from approaching closely enough to be injured during blasting, if their presence interferes with removal activities. • A fuel spill and clean up plan will be in place to mitigate any spills of fuel or hazardous chemicals that occur. 4.3-27
Condit Dam Hydroelectric Project Final Supplemental EIS Sediment Transport • The dam will be breached in late autumn to take advantage of the rainy season when there will be fewer adverse effects on aquatic life. • Dislodging unstable sediment and woody debris will help ensure that the reservoir sediment is transported downstream over the predicted three- to five-year period and does not affect long-term water quality, pool depths, or spawning gravels. • Heavy equipment should be used to cut channels through tributary lake sediment delta at Mill Creek to hasten the creation of a stable stream channel and prevent fish passage blockage by the sediment. • PacifiCorp has proposed to capture and transport to a hatchery the fall Chinook returning to the White Salmon River before the dam is breached in October to prevent the loss of a Chinook year-class. • PacifiCorp will take measures to coordinate with managers and protect the USFWS fish rearing facility at RM 1.4 from high flows and reservoir sediments. Dam and Appurtenance Removal • Use of BMPs will avoid or minimize impacts associated with the use of haul roads, staging area, and disposal sites, and filling the surge tank tailrace. • Cofferdam removal will either occur as soon as possible after dam removal and be accomplished by blasting while suspended sediment levels excluded upstream migrating fish, or mechanical means will be used rather than blasting. The cofferdam will be removed by May following dam breaching so that steelhead returning to the river can pass quickly upstream to less turbid areas of the stream or its tributaries. Post-Removal Management Upstream Sediment Management • After the initial dam breaching, sediment management will be conducted above the dam until all unstable slopes have been stabilized and areas of bare sediment in the former lakebed are revegetated. • Heavy equipment should be used to cut through the delta and lake sediments overlaying the Mill Creek (RM 4.0) channel to avoid barriers to fish passage forming at head-cuts and to shorten the time required to stabilize the stream channel. • If blasting is used to stabilize slopes or remove debris, it should be confined to daylight hours when salmonids are least likely to be actively moving. This will reduce the number of fish exposed to hydrostatic shock from blasting activities. 4.3-28
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Condit Dam Removal Final SEPA Suppl
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March 23, 2007 Dear interested part
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Condit Dam Hydroelectric Project Fi
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Appendix A Memorandum of Agreement
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Appendix C Supplemental Aquatic Res
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Agency and Organization Letters and
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Agency and Organization Letters Con
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Contents Public Meetings Response P
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Contents Individuals Individuals A-
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