The report to the Legislature is one of two feasibility studies that will help determine the fate of Enloe Dam.
‘Go/no-go’ decision could come in 2025
A decision about whether to remove Enloe Dam could be made by the end of 2025, according to a report on the feasibility of removing the dam provided to the state Legislature at the end of June.
The 20-page report — backed by hundreds of pages of appendices — provides a comprehensive overview of the history of the dam and options for removal. It summarizes analyses of the nearly 3 million cubic yards of sediment backed up behind the dam.
Enloe Dam, located on the Similkameen River near Oroville, hasn’t produced power in 65 years. The Okanogan Public Utility District (PUD) acquired the dam by eminent domain in 1942. For several decades, the PUD developed plans to re-energize the dam, but the district abandoned that goal in 2018 when the electrification proved financially unfeasible, according to the report.
Substantial research is necessary to get to the “PUD go/no-go decision,” according to the report.
If the PUD decides to remove the dam, a comprehensive design for removal and necessary permits would be in hand by the end of 2027, with dam removal taking place over one to two seasons in 2027 and 2028, according to the report. That would be followed by 10 years of monitoring.
The report looks at sediment analyses by state and federal agencies. Research done this year by the Washington Department of Ecology found elevated concentrations of arsenic, most likely connected with historical mining upstream of the dam.
The Ecology study concluded that the arsenic contamination is not severe enough to meet state and federal criteria for hazardous waste. Sediment thickness ranged from 6.5 feet at the upstream end of the impoundment to 40 feet immediately upstream of the dam. Sulfide concentrations were also elevated, but PCBs and pesticides were all below laboratory values, Ecology said.
Still, any dam-removal plan would have to include sediment management. The report summarizes three alternatives — allowing sediment to naturally flow downstream, dredging and disposal of sediment, or a combination of the two.
Releasing a large volume of sediment could affect habitat and properties adjacent to the river, according to the report. Dredging or excavating sediment increases costs and would require a suitable location for disposal. Depending on the degree of contamination, sediment could be distributed on level ground near the dam. Sediment can also be incorporated in construction fill, levee construction, or concrete production, according to the report.
Cost estimates for sediment management range from $30 million (for it to flow downstream) to $290 million (disposal at a commercial landfill).
Dam-removal entity
The report evaluates entities that have the necessary authority to take on full responsibility for dam removal.
Most state and federal agencies considered as candidates don’t meet all the requirements, particularly because they can’t hold property interests or obtain necessary permits or insurance. The likeliest candidates for dam-removal entity are the Confederated Tribes of the Colville Reservation or a nonprofit or limited-liability corporation, according to the report.
The Washington Department of Fish and Wildlife (WDFW) could potentially oversee removal, since it has authority to own and demolish infrastructure. But additional legislation, giving WDFW the authority to acquire Enloe Dam solely for the purpose of removing it, would be necessary, according to the report.
Interviews with stakeholders indicate interest in dam removal for habitat restoration — in particular, opening cold-water refugia for fish, particularly given the impacts of climate change. There was also interest in maintaining irrigation and grazing permits, in ecotourism, and in preservation of some dam structures as a historical monument. In addition to the dam, there’s a powerhouse, above-ground penstocks and surge tanks.
Interest in dam removal has grown as research by fish biologists indicates there could be more than 300 miles of habitat for endangered steelhead and spring Chinook in the Similkameen River in British Columbia.
Last year, the PUD commissioners adopted a resolution supporting a feasibility analysis of dam removal. Their requirements include finding an agency to handle dam removal that would release the PUD from all liability, as well as a source of funding to cover all costs of removal.
The Washington state budget allocated $250,000 to WDFW for the Legislative report. Trout Unlimited and the Colville Tribes worked together as the project team for the report.
Trout Unlimited and the Colville Tribes are also working on a comprehensive feasibility assessment and alternatives analysis funded by a two-year, $2.31-million grant from the National Oceanic and Atmospheric Administration. The contract for that work is being finalized, according to Warren Colyer, western water & habitat program director for Trout Unlimited.
