County mulls options to acquire water rights in Chehalis Basin


Thurston County is looking to acquire up to 2,650 acre-feet of water rights in the Chehalis Basin.

The Board of County Commissioners, together with the Community Planning and Economic Development Department, discussed how much they could purchase and how they could acquire the water rights during a meeting Thursday, September 7.

Power generation company TransAlta currently owns the water rights for its coal-fired Centralia Power Plant operations.

The Centralia Power Plant is expected to close in 2025, so the company is making its water right available for purchase at $2,750 per acre-foot.

Associate Planner Bryan Benjamin said that staff reviewed recent water rights purchases of other entities in the state and found that a comparable purchase would be typically priced around $10,000 to $25,000 per acre-foot.

Benjamin said that the acquisition of the water rights would be a “once-in-a-generation opportunity” due to its low cost and the purchase being a one-time flat fee. He also noted that purchasing these water rights from the company is a “proven concept” as Centralia and Chehalis are already jointly under contract to purchase around 6,720 acre-feet of water rights from TransAlta.

Benjamin briefed the board on three possible scopes of action to determine how they could acquire the water rights. The three choices are non-exclusive and can all be pursued by the county should the board give the signal.

Mitigation for Grand Mound Public Water System

The first option is to purchase about 200 acre-feet of water rights as mitigation for the Grand Mound Public Water System.

Benjamin said that a conservative cost for the purchase is about $690,000, which the county could take from the Capital Improvements Program fund.

The county had planned to use the funds for a new water reclamation facility, which would have cost around $5 million, supposedly as a required mitigation for the permit of Grand Mound Public Water System.

Water Resources Utility Planner Aaron Tormanen explained that the county has an ongoing agreement with the Department of Ecology requiring the county to produce Class A reclaimed wastewater by 2025 as mitigation. There was a past assumption that the water system was negatively impacting the flow of Prairie Creek. Still, Tormanen said that ongoing monitoring now suggests that the creek's flow is heavily influenced by rainfall and the rainy season rather than groundwater.

Mitigation for permit-exempt wells

The second option would be to use the water rights as mitigation for permit-exempt well installations in the Chehalis Basin as mandated by the Streamflow Restoration Act.

The Chehalis Watershed Management plan identifies the acquisition of water rights as an opportunity to offset the impact of permit-exempt wells in the watershed.

Benjamin said that the acquisition of water rights could account for 350 to 505 acre-feet of offset benefits, which could cost around $1.7 million.

The county could apply for Streamflow Restoration Act competitive grants to fund the purchase. Applications for the grant are due in the first quarter of 2024.

Long-term water allocation

The third option is the largest in scope and involves the creation of a long-term water allocation program to manage water resources for a variety of applications.

Benjamin said that portions of the water rights could be purchased to seed the program with a maximum purchase of about 1,945 acre-feet of water for about $5.35 million.

Funding for the program can be made possible through state and federal grant programs. Benjamin added that Thurston Conservation District has expressed interest in partnering with the county for the management of the program.

To determine their next steps, Commissioner Carolina Mejia instructed staff to inform TransAlta of the county’s interest in acquiring the water rights before developing a financial plan to assess the county’s capacity to follow through with the three options.


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