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.

Construction impacts will last only a few months. 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. Noise from construction activities related to the outfall will not be excessive.

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 window. 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. WES will follow the Oregon State Historic Preservation Office project review process and regulations, and continue to work with the Grand Ronde Tribal Historic Preservation Office.

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.

WES will deploy conservation measures to ensure that seals and sea lions, which may be present if fish are abundant, are not impacted by construction. 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 of the outfall pipe in the river will follow in-water work windows established by the Oregon Department of Fish and Wildlife (July 1–Oct. 31 and Dec. 1–Jan. 31). Construction of the land portions of the outfall could occur at any time during the year. Construction is anticipated in 2024 and 2025, with operation starting in 2025.

In addition to returning park property to its original condition, the project will also include enhancements to the park and surrounding areas, which may include native landscaping, riverbank restoration, trails and other needs identified by the City of Oregon City Parks and Recreation Advisory Committee.

At this time, it is unknown if the park will need to be closed for any portion of this project. If the park does close, the closure time will be limited in duration and only impact the area of the park adjacent to construction.

It is anticipated that the Jon Storm Park dock will need to be closed for the in-water portion of construction of the outfall. Every effort will be made to keep the closure time to a minimum. WES will work closely with the City of Oregon City as potential impacts become clear.

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.

Tunneling will not have an impact on the groundwater. Tunneling will not weaken the road or create a sinkhole. The outfall tunnel will be installed much deeper than the road subgrade.

Access to the hotel will not be affected by construction. Additional information is being gathered and assessed to confirm tunneling options, which is WES’ preferred installation method. Tunneling would minimize impacts to local roads.

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.