Condit Dam Removal Condit Dam Removal - Access Washington

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Condit Dam Hydroelectric Project Final Supplemental EIS 1.4 FOCUS OF SEPA SEIS The focus of this SEPA SEIS will primarily be on the “Settlement Agreement with Modifications” Alternative since it was the FERC staff-recommended alternative in their FSFEIS. The issues identified by Ecology for additional assessment as part of the SEPA process include: increased erosion, sedimentation, and turbidity in the White Salmon River from dam breaching and removal; impacts to water quality in the White Salmon River and Columbia River; impacts to groundwater quality; increased turbidity in stormwater runoff; effects on fish; potential barriers to fish passage; potential effects on priority species and habitats due to clearing vegetation or grading staging areas; loss of wetlands; sedimentation or scour of wetlands; impacts to local roadways; impacts to air quality and potentially to human health from fine particles; construction noise; land use impacts; visual impacts from reservoir and vegetation removal; public safety; impacts to public services including temporary interruption of water supplies and increased need for services of local police and fire personnel; and possibly local permits. (See Section 2.4 for a complete list of issues.) 1.5 DESCRIPTION OF PROPOSED ACTION The existing Condit Hydroelectric Project includes a concrete dam, an approximately 1.8-milelong reservoir, a 13.5-foot-diameter wood-stave pipeline of approximately one mile in length, a reinforced-concrete surge tower, two 650-foot-long penstocks (one steel and one wood), and a powerhouse structure housing two turbines with an installed capacity of 14,700 kilowatts (Figure 1-1). The proposed action includes draining the reservoir through a tunnel that would be constructed through the dam, removing the dam, removing the wood stave pipeline, the surge tower and the two penstocks, and partial filling of the tail race at the power house. Concrete and wood from the pipeline would be disposed of and/or staged for recycling on property near the dam. Details of the proposed action are described in the Condit Hydroelectric Project, FERC Project No. 2342, Project Description (PacifiCorp 2004). The project description includes numerous plans designed to minimize or eliminate potential impacts related to the project. The stages of the project are: pre-dam removal activities, dam breaching and removal, and post-removal management. The activities associated with each of these stages and the project schedule are summarized below. 1.5.1 Pre-Dam Removal Activities • In order to perform the removal and associated restoration work, temporary work areas, staging areas, and access roads would need to be established and utilized. These staging areas and access roads are located on the east side of the White Salmon River in proximity to the dam. • A fueling station would be located at staging area SA-2 adjacent to the dam. Fueling of remote equipment, such as cranes or highlines would be accomplished by tank trucks and would use required preventative and protective measures against spills. 1-3
Condit Dam Hydroelectric Project Final Supplemental EIS • A new temporary water supply pipeline would be installed across the lake with a cable support system before the dam is breached in order to assure that service from the existing pipeline is not interrupted by a potential failure during dam breaching. After the reservoir is drained and sediment has been stabilized, a new permanent water line would be installed. • The supports for Northwestern Lake Bridge, located 1.8 miles upstream from the dam, would be modified to enable the bridge to withstand the long-term scouring action of the river channel. • Mount Adams Orchard currently withdraws irrigation water from Northwestern Lake. A new intake and pump system or well would be designed and installed near the current dam in coordination with Mount Adams Orchard personnel to assure the needs of the orchard are met. • Prior to draining Northwestern Lake, the hardware on the crest of Condit Dam would be removed and a 12-foot-high by 18-foot-wide, slightly bell-shaped drain tunnel would be excavated from the downstream side near the base of the dam to provide rapid reservoir drainage. 1.5.2 Dam Breaching and Removal • Prior to the blast that opens the final 15 feet of the drain tunnel, a barge-mounted clamshell crane would be used to excavate sediment and debris from the upstream face of the dam in the area where the tunnel would be opened. • The final 15 feet of the tunnel would be breached by blasting out the remaining concrete. The tunnel size would allow an approximate maximum flow of 10,000 cubic feet per second (cfs) to pass through. At this tunnel size, the reservoir pool is expected to lower to stream level within six hours, causing substantial amounts of sediment and woody debris currently trapped behind the dam to be flushed downstream. • In order to assure that the drawdown/stabilization process is successful, an assessment of slope conditions would be made to determine whether active management of the sediment would be required. Options for active management of the sediment include the use of water cannons, blasting charges, and/or mechanical means. • Once the reservoir is drained, the concrete dam would be cut and blasted into large blocks or rubble. This concrete would be loaded with either a crane or a highline yarder-type system onto trucks and then hauled to an 8-acre storage/disposal area located a few thousand feet upstream of the dam and owned by PacifiCorp. If a concrete recycling recipient is available, then the disposal site would be a transfer site or a temporary storage site. • Historic photographs and drawings show that a cofferdam system was used in the original construction of the dam and was left behind in the reservoir and subsequently flooded. It is hoped that this structure can be removed by blasting and the use of a 1-4
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Page 3 and 4: March 23, 2007 Dear interested part
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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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Condit Dam Removal Condit Dam Removal - Access Washington

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