Willamette Water Supply Program

Over the next 50 years, the water needs of Washington County—one of Oregon’s fastest-growing regions—are expected to double. The region’s current water infrastructure is also vulnerable to seismic events, further threatening the area’s water resources. To future-proof the region’s drinking water supply, the Tualatin Valley Water District, City of Hillsboro, and City of Beaverton teamed up to develop the Willamette Water Supply Program (WWSP), the Pacific Northwest’s largest water conveyance program. Rather than scaling up the three entities’ existing water supply systems, the WWSP is developing an entirely new source of water, drawing on the Willamette River to supply their customers. The resulting Willamette Water Supply System will provide the three jurisdictions with a robust drinking water supply that can both meet future demand and withstand major seismic events.

In 2017, WWSP selected Carollo Engineers as a project partner to provide both program and construction management services. The project’s scale and complexity required a sophisticated approach: The WWSP includes more than 30 miles of seismically resilient, 48 to 66-inch-diameter transmission pipelines that span several jurisdictions; a raw water pump station; a 15-million gallon water storage tank with room to add an additional tank; and a state-of-the-art, 60-million gallon per day (mgd) water treatment facility that is designed to expand to 120 mgd. Carollo, in partnership with the project team, oversaw the intake, treatment facilities, reservoirs, and large-diameter pipelines.

Minimizing disruption to the community also required creative approaches. For example, some system components, such as segments of transmission pipe, were completed as much as eight years in advance to correspond with planned roadway construction, reducing construction impacts and keeping costs in check. The project team also modified the routing of some pipe segments from farmlands with no roadway access to parallel planned roadways, which improved buy-in from local growers while also providing improved access for construction and future maintenance. Thanks to the project team’s efforts, overall program change orders currently stand at just 1.8 percent.

When the Willamette Water Supply System is complete, it will be one of the most seismically resilient water systems in Oregon and the broader Pacific Northwest. It will also provide a variety of community benefits: Thus far, the project has created 4,168 jobs, and the new system will provide exceptional finished water quality, enhanced system safety, and greater source reliability and redundancy for the region’s growing population. As such, this project provides a model for other water utilities across the country that are grappling with aging infrastructure, population growth, and increasing climate uncertainties.