NorthWestern presents findings

NorthWestern Energy has taken another step toward relicensing the Thompson Falls Hydroelectric Project. In a public meeting held in Missoula, the company outlined seven different studies and findings as part of their efforts to renew their license with the Federal Energy Regulatory Commission (FERC) before the 2025 expiration. The seven different studies coincide with FERC’s licensing process that evaluates the effects of a project based on a nexus to continuing project operations.

During the beginning of 2021, NorthWestern proposed a series of different studies that would evaluate the future effects of the reservoir. After taking comments from representatives from the Fish, Wildlife and Parks, U.S. Fish and Wildlife Service, United States Forest Service and Montana Department of Environmental Quality (DEQ), a Revised Study Plan (RSP) was developed. In May of 2021, FERC issued a Study Plan Determination that directed NorthWestern to conduct seven of the studies proposed in the RSP.

NorthWestern conducted a study of operational scenarios to determine the potential impact on Thompson Falls Dam’s resources and reservoir. A second study of total dissolved gas was conducted at the Main Channel Dam and at Birdland Bay Bridge in order to meet the DEQ’s water quality standards in the reservoir. The water quality standard was developed to protect fish from high levels of total dissolved gas, which NorthWestern’s summary report says can cause gas bubble trauma that can lead to injury and possible death to fish. A hydraulics study was conducted to characterize the velocity field and water depths between the main channel dam and High Bridge. A Radio telemetry study of salmonids was conducted to evaluate movement paths, rates and behavior in response to hydraulic conditions. A survey study was conducted at 10 recreation sites on or near the reservoir and the Clark Fork River below the dam. Another study was conducted in order to update NorthWestern's inventory of the historic architectural and engineering properties, as well as identifying areas where there was a high probability for future occurrences of prehistoric or historic archaeological properties that could be affected. The final study was to update a literature review of the downstream fish passage. It was determined that downstream studies of water quality, fish and other aspects of the Thompson Falls reservoir were not needed.

The findings from the seven conducted studies will be used to prepare for the final license application. Study reports on each of the seven studies were presented in separate reports and filed with FERC. The executive summary of the findings and the study plan implementation schedule can be found at northwesternenergy.com.