Oregon, United States After nearly a century of serving PacifiCorp customers, Condit Dam on the White Salmon River in south central Washington will start to be removed this fall, fulfilling a multi-party settlement agreement signed in 1999.
Decommissioning the hydroelectric project is now moving forward after receipt of an essential sediment management permit from the U.S. Army Corps of Engineers, the final major regulatory step. In December, 2010, PacifiCorp received a surrender order from the Federal Energy Regulatory Commission providing for dam decommissioning.
The project is located about 3.3 miles upstream from the confluence of the White Salmon and Columbia Rivers. Project facilities consist of a 125-foot high, 471-foot long concrete gravity diversion dam, and an intake structure that directs water into a 13.5-foot diameter by 5,100-foot long wood stave flow line.
The powerhouse contains two double horizontal Francis turbines with an installed capacity of 14.7 MW (enough to power about 7,000 average homes for a year). The project creates a reservoir, Northwestern Lake, which extends 1.8 miles upstream of the dam and covers about 92 acres.
The commission modified the surrender order on April 21, which, with the Corps permit, provides the regulatory certainty PacifiCorp needed to proceed to remove the 125-foot high dam. On June 8, 2011, the commission completed review and approval of requisite project removal design and resource management plans.
Dam removal was determined to be less costly to PacifiCorp customers than the fish passage that would be required for operation as part of the federal dam relicensing process. The cost of decommissioning Condit is currently estimated at about $32 million, including funds already spent during the planning process.
Plans call for a summer full of meticulous preparation before a carefully planned breach in October releases Northwestern Lake through a 13-foot hole blasted out near the base of the dam. Steps to be completed before the breach include the initial excavation of the 90-foot long drain tunnel, dredging the upstream side of the dam at the drain tunnel, work to strengthen a bridge that crosses Northwestern Lake, and also relocating a water pipeline that crosses the reservoir.
After the initial breach and draining of the reservoir in October, demolition of the remaining portion of the dam is scheduled to begin in spring 2012 and be completed by August 31, 2012. Restoration work throughout the former reservoir area is slated for completion by the end of 2012.