In response to a proposed dam on the Chehalis River near Pe Ell, a report has been released that assesses the risk of a possible increase in rates of mercury bioaccumulation.
The report, written by a master of environmental studies student from The Evergreen State College with support from the state Department of Ecology staff, evaluates the characteristics of a dam with a proposed reservoir and reviews mercury data from lakes and reservoirs in the state.
One design proposed for the dam would create a permanent reservoir for flood retention and flow augmentation. The dam is referred to as an FRFA structure. Another option under consideration would only create a reservoir during flooding events.
“Results suggest that, if built, the FRFA reservoir would be conducive to mercury methylation and bioaccumulation, which could reach levels higher than found in other waterbodies in Western Washington, particularly in the short-term,” states a description of the report. “Recommendations are offered for future studies to increase understanding of methyl mercury in reservoirs.”
Those recommendations include studies that monitor fish tissue, sediment and the water column in other reservoirs.
If the FRFA reservoir is selected, the report states the reservoir could result in mercury concentrations in fish tissue that could reach higher levels than currently found in the Chehalis River system, according to a press release.
“The risk assessment examined the factors known to affect mercury bioaccumulation, analyzed the expected characteristics of the proposed reservoirs, compared mercury data from lakes and reservoirs in Washington State, and identified existing gaps in data and knowledge,” according to the release.
The report, titled “Chehalis River Proposed Flood Retention Reservoirs: A Review of Potential Mercury Impacts,” is available online at https://fortress.wa.gov/ecy/publications/SummaryPages/1703015.html.