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The three options to make the dam seismically safe are more expensive than the project team initially thought.

PMG FILE PHOTO - Scoggins Dam west of Hillsboro has long been in need of repair. Work is underway to determine whether crews should rebuild the aging structure or construct something new farther downstream.

Cost estimates up to 40% higher than expected have delayed an expected decision on the future of Scoggins Dam and Henry Hagg Lake.

Clean Water Services, which manages wastewater and stormwater for the urban areas in Washington County, says the dam needs safety upgrades to make it seismically safe and to meet the community's long-term needs.

"Doing nothing is not an option," the agency's project website says.

The three options for upgrading the dam are modifying the dam in its current location, raising and modifying the dam or adding a new dam downstream. Currently, the estimates range for the options range from $770 million to $1.2 billion, according to a spring newsletter about the project.

Hagg Lake and Scoggins Dam provide water for nearly 400,000 residents and irrigation for 17,000 acres of cropland, according to the website.

"It's a safe structure right now, and it operates safely every year, but it can't withstand a Cascadia subduction zone earthquake," said Tom VanderPlaat, water project manager and strategic business associate for Clean Water Services.

The project team got the higher cost estimates in March 2020. Around the same time, the coronavirus pandemic reached Oregon. Between the pandemic and the costlier-than-expected projections, their plans changed.

"Because we got assessments that were above what we anticipated they would be, it sent us both — (the U.S. Bureau of) Reclamation and ourselves — back to the drawing board, due to just the ability to fund that large of a project," VanderPlaat said.

Most funding for the upgrades will come from the U.S. Bureau of Reclamation, which is working with Clean Water Services on the project. Local partners that share the water in the lake will repay 15% of the seismic improvement costs, according to the project website. These include Tualatin Valley Irrigation District, Clean Water Services, Lake Oswego Corporation and the cities of Hillsboro, Beaverton and Forest Grove.

Overall, more economic and financial research, analysis and vetting is needed before choosing an option for the dam, especially given the high price tag.

The project team has already done preliminary environmental analyses identifying some environmental impacts, but they haven't yet gotten to the point of deciding how to mitigate for and adjust to those impacts.

Ashley Short with Tualatin Riverkeepers, a community-based organization that protects and restores the Tualatin River watershed, said she has been kept up to date with updates on the project, even though it's so early in the process since the agencies have basically had to go back to the beginning.

"We are supportive of them taking a pause and looking into more information, because it is a lot of money and a really important project," Short said. "So, it's important that we do a lot of studying and analysis to ensure that whatever investment happens in the basin is going to be effective."

Each option for the dam is going to have different environmental impacts, Short said, but some of them might include inundating oak habitat and elk grazing areas and affecting fish habitat and activity. Flooding could also introduce contaminants, since there is a lumber mill in that inundation area, she said.

Once environmental impacts are fully considered and an option for the upgraded dam is decided, construction on the project will likely not begin before 2028, according to the project newsletter. And once it does begin, construction could take up to eight years.

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