Condit Dam Removal Condit Dam Removal - Access Washington

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Condit Dam Hydroelectric Project Final Supplemental EIS Table 1-1 (Continued) Summary of Impacts and Mitigation Measures Impacts Mitigation Aquatic Resources Pre-Dam Removal Activities Pre-Dam Removal Activities Haul Roads, Staging Areas, and Disposal Sites Haul Roads, Staging Areas, and Disposal Sites • Sediment movement and deposition as well as other water quality effects could affect aquatic organisms. • Mitigation measures applied for water quality maintenance and sediment management will also protect aquatic organisms. Northwestern Lake Northwestern Lake • Work at the Northwestern Lake bridge could affect aquatic organisms. • 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 Dam Breaching and Removal Drain Tunnel Drain Tunnel • An increase in pH from concrete particles in water could kill aquatic organisms if it goes above pH 9. • Water used in drilling into the dam to develop the drain tunnel will be collected and removed from the site. Air drilling may be used, in whch case water collection would be needed. • 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 in the water can directly kill fish that are too close to the source. • Blasting will be accomplished in accordance with the Blasting Plan (PacifiCorp 2004). • Spilled fuel is toxic to aquatic organisms. • A fuel spill and clean up plan will be in place to mitigate any spills of fuel or hazardous chemicals that occur. 1-17
Condit Dam Hydroelectric Project Final Supplemental EIS Impacts Sediment Transport • Transport of the mass of sediment from the reservoir downstream to the Columbia River will kill most aquatic organisms. The longer the high concentrations continue, the longer or more difficult it will be for fish to recolonize the reach of the White Salmon River below the Condit Dam site or anadromous fish to migrate up the White Salmon River. • Salmon trying to enter the White Salmon River to spawn while the mass of sediment is passing would be killed and no reproduction of anadromous fish will occur until levels of suspended fall below lethal levels and migration upstream above the upstream end of the reservoir to suitable spawning gravels becomes possible. • Sediment will likely fill the fish-rearing channels of the U.S. Fish and Wildlife Service’s fish rearing facility at river mile 1.4. Dam and Appurtenance Removal • The old cofferdam in the reservoir upstream of the dam is expected to be a barrier to upstream migration by anadromous fish. Post-Removal Management Upstream Sediment Management • Unstable or erodible sediments could continue to adversely affect the substrate habitat for aquatic organisms and slow recovery of habitable substrate. • The delta at the mouth of Mill Creek is likely to be a barrier to access by fish from the river. Table 1-1 (Continued) Summary of Impacts and Mitigation Measures Aquatic Resources (Continued) Sediment Transport Mitigation • The dam will be breached in October to minimize the risk of harm to seasonal fish runs. The timing would also take advantage of the rainy season when there will be fewer adverse effects on recreation and aquatic life. The high flows of the season will aid in transporting sediment from the reservoir. • Dislodging unstable sediment and woody debris will help ensure that the reservoir sediment is transported downstream quickly, therefore within the predicted 3–5 year period, and does not affect long-term water quality, pool depths, or spawning gravels. • 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 protect the fish rearing facility from high flows and reservoir sediments. Dam and Appurtenance Removal • Cofferdam removal will either occur as soon as possible after dam removal and be accomplished by blasting while suspended sediment levels exclude 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. • If the delta is a barrier on May 1 at the year following dam removal, heavy equipment would 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. 1-18
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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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Contents Public Meetings Response P
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Contents Individuals Individuals A-
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