Tri-City Water Resource Recovery Facility Outfall Project

The outfall diffuser will contribute to fish recovery in the Willamette River. Its location will be about 1,600 feet upstream of the existing outfall in a deep, stable aquatic bed feature that will better mix and dilute treated wastewater as it enters the Willamette River. It will maintain the existing cold-water fish refuge area at the mouth of the Clackamas River, and minimize future maintenance needs. This will also ensure the water meets state water quality standards, including water chemistry characteristics that fish need.

Once complete, the outfall will operate without any obstructions to current river uses. Trenchless technologies will be used to minimize impacts to nearby properties and parks. 

Construction is anticipated in 2024–2025 with operation starting in 2025.

The outfall will be completely buried and not visible. The outfall will be beneath the river and only smaller pipes will penetrate the river’s bottom. They will be in a deep segment of the river and will not interfere with boating, recreation or aquatic life.

The diffuser section of the pipeline will be buried under the riverbed, extend beyond the middle of the river and will be located at a particularly deep spot for better mixing that will enhance water quality. The actual diffuser ports will extend up above the diffuser bed. The diffuser is an improved river discharge mechanism that will be built at the end of the outfall.

Construction crews will strictly adhere to the Oregon Department of Fish and Wildlife’s Willamette River in-water work requirements. The in-water work guidelines were created to minimize potential impacts to fish, Pacific lamprey, wildlife and habitat resources.

The model-predicted dilutions for the preferred 150-foot long outfall diffuser have been developed using current and future wastewater flows and maximum summer temperatures. The modeled results demonstrate this outfall will be well below the Oregon water quality temperature standards. The design of the diffuser will ensure that the outfall discharge stays well below any temperatures that could affect biological resources.

WES is actively designing the project to avoid known archaeological resources in the vicinity of the project and will complete a due diligence effort to identify any previously unidentified cultural resources that may be affected by the project. 

There will be no impacts on the fishery after construction is completed and the outfall is brought online. The outfall location will provide better mixing, which will help improve overall water quality in the river.

The improved diffuser will ensure that treated wastewater doesn’t disrupt the natural environment and keep the river clean for swimming, boating, fishing, and aquatic life.

Construction should not impact Abernethy Creek. The tunnel will not be going through bedrock, as bedrock is deeper than our anticipated tunnel corridor. The location of the new outfall diffuser in the Willamette River and the most inshore diffuser port location is approximately 400 feet distance from the mouth of Abernethy Creek. This substantial offshore location will allow a wide inshore region for fish migrating into Abernethy Creek. The project will specifically design the river diffuser ports and velocities to remain below the National Marine Fisheries Service’s “guidance” of less than 8 fps for outfall ports to avoid fish attraction.

Providing additional outfall capacity and reducing the amount of Infiltration & Inflow of extra water in the collection system will reduce the risk of potential sewer overflows.

Construction will use a design-build process, where the design engineers and builders work together under a single contract from the beginning of the project. This method ensures the project stays on schedule and on budget.