Avista Corp, NorthWestern Energy, agree to Colstrip ownership transfer

Tom Lutey Holly Michels

NorthWestern Energy will increase its share of Colstrip Power Plant in 2026 under an agreement with Spokane-based Avista Corp, the two utilities announced Monday night.

The transaction is timed with Avista’s state deadline to stop delivering coal power to its Washington customers by the end of 2025. The handoff resembles one announced last August between another Washington utility with a Colstrip stake, Puget Sound Energy, and power plant co-owner Talen Energy.

Avista’s 222-megawatt share of Colstrip is divided between the powerplant’s surviving generators, Units 3 and 4. Dan Vermillion, Avista CEO, told an audience gathered for a lobbying event at the Great Northern Hotel in Helena that the terms are still being set, but that the company will keep its environmental cleanup liability, as well as its share of the Colstrip transmission line.

“When we exit the facility, we will continue to honor our commitments to the Colstrip plant and community. The transaction recognizes our commitment to fund our share of the plant decommissioning costs,” Vermillion said.

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“And we anticipate that there will be other opportunities for us to partner

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