Lake Oswego Wastewater Treatment Plant Project

The cities of Lake Oswego and Portland are exploring the option of designing a new, more efficient wastewater treatment plant to replace the existing Tryon Creek Wastewater Treatment Plant (TCWTP), which needs significant investments to meet necessary Oregon Department of Environmental Quality requirements.


The existing plant, strategically located at the confluence of Tryon Creek and the Willamette River, was constructed in 1964 and expanded in 1976. The current plant is owned by the City of Portland and operated by the Portland Bureau of Environmental Services (BES). TCWTP treats sewage collected from parts of southwest Portland, unincorporated areas of Multnomah and Clackamas counties, and the City of Lake Oswego. Treated wastewater is discharged to the Willamette River via an outfall system.

Currently, wastewater treatment operations and maintenance costs are split between Portland and Lake Oswego. On average, Lake Oswego contributes approximately 70 percent of the flow volume.

About the Project

In 2014, BES completed the TCWTP facilities planning process that identified current and future capital improvements to the plant required to ensure the plant continues to meet BES levels of service and regulatory requirements for the next 30 years. The plant is aging and in need of a major upgrade or replacement over time to meet increasingly stricter treatment standards and to become more efficient at managing existing wastewater concerns.

In 2018 the City of Lake Oswego received a high-level study analyzing the technical and financial feasibility of a new replacement plant and found that a new replacement plant may cost the same or even less than the cost of upgrading and maintaining TCWTP over the coming years.

As a result, the City is exploring the option to build a new wastewater treatment plant, which will replace the aging TCWTP, subject to pre-established affordability thresholds.

Public-Private Partnership with EPCOR

Through a competitive bidding process, the cities of Lake Oswego and Portland have partnered with EPCOR Foothills Water Partners (EFWP) under a Public-Private Partnership (P3) to Design-Build-Finance-Operate-Maintain a new plant. This minimizes the cities’ risks and costs. The intention will also be to transfer the ownership of the wastewater treatment plant from the City of Portland to the City of Lake Oswego.

Council reviewed the P3 proposals at a special study session in April 2021, ultimately approving a Preliminary Services Agreement with EFWP in May 2021.

Goals and Benefits

The goals of the project are:

  • Keep costs at a level equal to or below the cost of upgrading the TCWTP
  • Optimize risk transfer to the private developer
  • Obtain a reliable plant design that is more compact, requires a smaller footprint, and would be a better neighbor to the existing and future development through odor control and a more visually appealing design
  • Achieve the earliest date of operations that is consistent with reliable, high‐quality design and construction
  • Achieve reliable operations and effective maintenance
  • Minimize life cycle costs, consistent with the above objectives

The option of a new facility would require a smaller overall footprint and elevate the cities’ environmental commitment by increasing the amount of water treated to newly prescribed waste standards and returned to the river to the natural water cycle. It would also be a good neighbor to the existing and future waterfront development through odor control and a visually appealing design.

Project Timeline

Site Investigations & Preliminary Design – Summer - Early Fall 2021

Design Development – Fall 2021 - Spring 2022

Final Design – Summer – Early Fall 2022

Permitting – Summer 2021 – Fall 2022

Construction – 2022 – late 2024

Get Involved

A robust public involvement process will seek community feedback and stakeholder input to help shape the design of the facility.

Upcoming outreach events and opportunities will be updated and shared on this website. Stay tuned for more information!