Will analyze the sediment behind the dam for toxins
Tens of thousands of endangered salmon could gain access to high-quality habitat in the Similkameen River watershed if the Enloe Dam were removed, but any dam demolition project would need to address arsenic contamination in the sediment collected behind the dam under deep gravel.
At a community meeting on Enloe Dam in Tonasket last week, federal, state, and tribal biologists and hydrologists, along with representatives of the Colville Tribes, presented findings from preliminary sediment analysis and potential for rainbow trout and spring chinook to reach habitat in British Columbia. The presentation also included a tribal perspective on the Similkameen River and the regional watershed.
With extremely low return rates to the Okanogan watershed in recent years – only 87 adults of native origin have survived this year – “The importance of removing Enloe Dam is probably the only chance that these animals have to survive,” said Colville Confederate Tribes biologist Chris Fisher. .
Fish habitat research and sediment sampling have intensified over the past three years, since the Okanogan County Utility District (PUD), owner of Enloe Dam, decided in 2018 that “It was not cost effective to re-energize the dam for power generation,” Fisher said.
As people wonder what to do with the dam, which hasn’t generated electricity for more than 60 years, questions have been piling up about what’s in the sediment, how much it would cost to remove the dam and clean up the toxins, and who would pay for it, Fisher told the 70 people who came to learn about Enloe. The PUD was asked to provide an update on the dam safety inspections they conducted, but declined, Fisher said. A PUD commissioner attended the presentation, he said.
It’s too early to say what it would cost to remove the dam, as it would depend on the nature of the contamination and how to deal with it safely, according to the presentation.
There are about 2.8 million cubic meters of sediment behind Enloe Dam, an amount that would fill 294,000 truckloads of cement, said Andrew Spanjer, a hydrologist with the US Geological Survey (USGS).
The USGS began collecting silt, clay, and sand sediment samples from various depths in the river in 2019. They obtained more than 100 samples in total, including material in the river bed under gravel and cobbles, where the oldest sediments were deposited, Spanjer said. There was concern about the potential for contamination due to mining upstream of the dam in the late 19th and early 20th centuries.
The USGS analyzed the samples for 54 trace elements and metals, including copper, arsenic and mercury, all of which can be toxic at high levels. They did not find high concentrations of copper, cadmium, lead or zinc. The mercury was well below the level that would cause concern and require a cleanup, Spanjer said.
But arsenic concentrations in a third of fine sediment samples — especially in deeper areas — exceed the toxicity threshold, Spanjer said. Fine sediment represents a small fraction of the total sediment retained behind the dam. Most of the coarser material samples did not have high concentrations of arsenic, he said.
Despite the high arsenic levels, the fine sediment is so deep and under so much clean gravel that it does not enter the Similkameen River system, meaning fish and people are protected, Arthur Buchan said. , a Washington Department of Ecology toxicologist. There is no concern unless the material is disturbed, he said. Ecology began its own sampling upstream and downstream of the dam late last year.
Ecology not only examines what is in the sediment, but also whether contaminants bind to the sediment or leach into the surrounding soils. This analysis will help determine if they would need to take any action to prevent sediment from moving downstream if the dam were removed. If contaminants bind to sediment, it would be easier to remove them safely, Buchan said.
In addition to examining contaminants from historic mining, researchers are monitoring the impacts of active mining upstream of the dam in Canada, Spanjer said. They expect the data to be available in 2023.
There are still too many unknowns for a good estimate of what it would cost to remove Enloe. Depending on whether some or all of the sediment could be spilled onto adjacent land — or just allowed to flow downstream — dam removal could cost anywhere from $51 million to $3.3 million, Mike Brunfelt said. , fluvial geomorphologist at Inter-Fluve, a company that specializes in the restoration of rivers and which has participated in the removal of approximately 200 dams.
Brunfelt’s estimates were based on the assumption that the sediments are clean and safe and would not need to be transported to a special disposal site. If contaminated, costs could increase five to 10 times, Spanjer said. According to biologists, allowing this volume of sediment, even if clean, to enter the river system would present its own problems for the river and the fish.
About 1,520 miles of the total 3,420 miles in B.C.’s upper Similkameen watershed are accessible to fish, said National Oceanic and Atmospheric Administration fisheries biologist Morgan Bond. There are six routes above Similkameen Falls that chinook and rainbow trout could take to reach upper habitat, Bond said.
Canadian habitat could support 3.9 million chinook salmon in the spring and 9.8 million rainbow trout in the parr stage, during which young salmon are adapting to the river in preparation for their journey to the south. ‘ocean. The upper watershed also provides good habitat for spawning grounds, where salmon lay their eggs. It would support 77,863 chinook spawning grounds and 203,310 rainbow trout spawning grounds, Bond said.
While survival rates for salmon returning from the ocean to their natal river to spawn may seem grim – less than 1% of upper Columbia salmon typically return – this still translates to between 7,800 and 47,000 spring adult salmon. and 29,000 to 118,000 rainbow trout, Bond said. Steelhead is stronger and more athletic than the Chinook spring and therefore generally more efficient at traversing falls, Brunfelt said.
Two members of Aboriginal Outfitters shared a cultural perspective on the river. The nonprofit was established last year to raise awareness of the importance of land stewardship for a community that felt disconnected from the river, said Joy Abrahamson, chief executive of Aboriginal Outfitters. . Water and its central role in sustaining life has always been at the heart of indigenous peoples, who maintain sacred rituals to protect water from pollution, drought and waste, she said.
The Colville Tribes voted to remove the dam in 2017. The Upper and Lower Similkameen Bands in British Columbia also support the removal of the dam.
The Washington Department of Fish and Wildlife is analyzing the biological, management, and legal issues associated with the potential removal of the dam and the restoration of the Similkameen River through a reserve in the state budget . Their findings must be submitted to the Legislative Assembly by December 1.
A video of the presentation will be available online. The link will be on the Methow Valley News website once it is posted.