A Pacific Northwest dam removal project, said by its owner, the National Park Service, to be the largest of its type in the U.S., is one step closer to beginning after the recent completion of a new water treatment plant in Port Angeles, Wash. NPS officials expect contractors to proceed with dismantling Elwha and Glines Canyon dams on the Olympic Peninsula in 2012.

Photo: National Park Service.

Demolition and removal is to start in 2012.

Congress approved removal of both Elwha River impoundments in 1993. Demolition was scheduled for 2009, until rising costs for the $308-million project delayed the start to 2012.

The federal government ordered NPS to remove Elwha Dam, a 105-ft-high concrete gravity structure, and Glines Canyon Dam, a 210-ft-high concrete arch, in the Olympic National Park in northwest Washington state, following paper manufacturer Crown-Zellerbach’s failed attempts to relicense the dams. “Environmental studies showed that the cost of meeting salmon mitigation [requirements] was too high,” says David Thomas, the National Park Service project manager.

A $16.4-million federal American Recovery and Reinvestment Act grant expedited the project by one year with funds for construction of the Lower Elwha Klallam Tribal Fish Hatchery. A Dallas, Ore.-based general contractor, James W. Fowler Co., won the $16.4-million contract on Sept. 18. “The job will allow us to retain about 15 employees,” says Mark Weisensee, project manager with Fowler.

When built in the 1920s, Glines Canyon and Elwha dams blocked access to 70 miles of salmon habitat. When they are removed, millions of cubic yards of silt are expected to flow down the Elwha River and impact drinking-water supplies for Port Angeles, which draws drinking water from groundwater and the river.

“The water treatment plants downstream aren’t able to handle that,” says Thomas. The $24.5-million, 10.6-million-gallon-per-day Port Angeles plant now provides filtration for drinking water. Estimated project cost is $24.5 million. A separate 53-mgd water treatment plant, which serves a nearby paper mill, will be completed in March 2010.

The contract for the removal of the two dams is scheduled for award late in fiscal year 2010, with demolition slated for the spring of 2011.

According to the park service, the first step in the removal will be to lower by 15 ft the water level of Lake Aldwell, the reservoir impounded by Elwha Dam, using existing water intakes and spillways. The contractor then will excavate a temporary diversion channel through the left spillway to allow the lake to drain more.

Cofferdams then must be installed to direct reservoir outflow into a temporary diversion channel. Next, the contractor will pump out water remaining immediately behind the dam and remove the fill material under dry conditions. The dam structure will then be removed and the original river channel restored before the powerhouse and other structues are demolished and removed.