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Two plans call for strengthening and raising existing dam; a third proposes a new structure downstream with more storage. Agencies will decide alternative by December.

PMG PHOTO: PETER WONG - Tom VanderPlaat, center, of Clean Water Services explains one of the engineering alternatives for Scoggins Dam on a recent tour with Washington County commissioners, who serve as the governing board for the agency. Commissioners from left are Jerry Willey, Roy Rogers, Chairwoman Kathryn Harrington and Dick Schouten. They are standing on the road atop the earthfill dam.Washington County will soon face decisions about the future of Scoggins Dam and Hagg Lake.

Though three alternatives are being considered, the real choice boils down to a single question: "Do you fix the existing structure, or do you build a new one?"

That is how Tom VanderPlaat, water supply project manager for Clean Water Services, put it to the five Washington County commissioners, who are also the governing board for the agency.

Hagg Lake is the primary water source for much of the county.

The county manages Hagg Lake as a park, and several agencies — including Clean Water Services, which treats wastewater and manages stormwater for the urban part of the county — share the water released from Hagg Lake.

But Scoggins Dam is owned by the U.S. Bureau of Reclamation, which has the dam atop its list of structures likely to be imperiled by a major earthquake, such as one along the Cascadia subduction zone off the Oregon coast.

Scoggins Dam, an earthfill structure 151 feet high, was built in 1975.

The three engineering alternatives, in brief:

• Modify the existing dam with new fill on the downstream face.

• Modify the existing dam with new fill and raise its height, which would add capacity to the current 52,000 acre-feet in Hagg Lake. (The maximum water level would go up by 17.5 feet, adding 21,000 acre-feet and about 200 more acres of open water.)

• Build a new and narrower dam of roller-compacted concrete about two miles downstream of the current dam, near the current Stimson Lumber mill. Oregon has two such dams, on Willow Creek near Heppner — the nation's first, completed in 1983 — and Galesville on Cow Creek near Azalea, built in 1985.

The resulting reservoir would add 50,000 acre-feet, just about doubling the capacity of the current Hagg Lake, and 600 more acres of open water.

The current dam is about 2,700 feet across; a narrower dam would be 1,000 feet across.

County commissioners toured the dam and the proposed downstream site, and heard a briefing about alternatives, on a field trip earlier in February.

"Doing nothing is not an option," said VanderPlaat, who has held his current job 20 years.

"Public safety and securing our long-term water supply is paramount to protecting this critical regional resource," he added. "This is a generational investment that requires years of study and analysis to ensure all cost-effective approaches have been explored in order to move on to selection of the best option."

There are no cost estimates yet for the three alternatives. They will be determined once the engineering work is complete by the end of this year.

Process underway

The bureau is studying the first two alternatives, plus the accompanying environmental review. Clean Water Services is looking at the proposed downstream dam.

CWS has invested $18 million in the engineering and environmental review elements on the Joint Project. Reclamation has budgeted $3.6 million related to the dam safety work.

About half of Hagg Lake's stored water goes to the Tualatin Valley Irrigation District, a quarter to Clean Water Services, and most of the rest to the Joint Water Commission, which serves Beaverton, Forest Grove and Hillsboro.

A new dam would allow Clean Water Services to release more water into the Tualatin River, in addition to its discharges of treated wastewater, to improve water quality in a river once considered one of Oregon's most polluted. The ratio would be two parts of released water to one part treated wastewater.

It also would offer the potential of additional supplies for three cities — Beaverton, Forest Grove and Hillsboro — and the Tualatin Valley Irrigation District. However, as of now, most of the additional water from a new dam would be for in-stream flows for Clean Water Services.

A new dam also would add about 1,000 acres to Hagg Lake.

But a new dam would require the relocation of about two dozen residents — property acquisition is part of the process — and the Stimson Lumber mill.

VanderPlaat said that while a new mill site would require less acreage than the current operation, it also would have to have access to water, power and a rail spur — and to be close to timber supply, it likely would remain in western Washington County.

The mill has been at its current site since 1933, predating Scoggins Dam by four decades.

Next steps

Both agencies will have to choose one of the engineering alternatives by December, after which a one-year process for an environmental impact statement will start in January 2020.

Under a 1970 federal law, major federal projects must undergo such a review — and because of a recent order by the Interior Department, the parent agency of the Bureau of Reclamation, that review has been shortened from three years to one.

Assuming completion of the environmental impact statement without challenges, a preferred alternative would be selected in early 2021, permits issued and construction started in fall 2022 with a completion target of 2026.

Though there are no cost estimates yet for dam improvements, the bureau would pick up 85 percent and local governments 15 percent of dam safety work.

CWS and other project partners — Hillsboro, Forest Grove and Beaverton, Tualatin Valley Irrigation District and the Lake Oswego Corp. — will be responsible for the 15 percent local share of the dam safety engineering and construction costs.

Local governments must pick up the entire cost of additional benefits, such as increased water storage — and Clean Water Services customers would pay most of the tab if a new dam is built and the agency reserves most of the new storage for in-stream flows.

The Scoggins Dam project is the nation's first to proceed under a 2015 law that allows dam safety work to be integrated with other benefits, such as water storage.

Advocates of a new dam are seeking a fish-passage waiver from the Oregon Department of Fish and Wildlife — they say their proposed mitigation would involve the removal of a dam at Gales Creek and related improvements — but Tualatin Riverkeepers say they will oppose such a move.

"They haven't actually picked the new dam as the preferred project yet — they're just kind of doing this ahead of the rest," said Ashley Short, advocacy and public policy coordinator for the group.

"As far as I know, they haven't done an Endangered Species Act process. They're trying to get the fish waiver done first."

Short said later the group does not oppose a new dam or downstream mitigation, just that an environmental analysis should be completed before any action is taken such as a waiver.

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NOTE: Updates with additional information. Adds clarification of Tualatin Riverkeepers position.

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