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Major improvements underway for Portland’s main wastewater treatment plant

Press Release
Environmental Services is undergoing major construction at the City’s main wastewater treatment plant to protect water quality, replace aging infrastructure, and add seismic resilience. Construction is slated for 2024 completion and service will continue 24/7/365

The City of Portland Bureau of Environmental Services is constructing the largest set of upgrades to the city’s main wastewater treatment plant in half a century.  

The improvements will protect water quality, add seismic resilience to key portions of the plant, and replace equipment and buildings that have reached or exceeded their intended life span. 

Graphic of the plant showing the work area
The multi-year project will have several work zones

“Every Portland resident, business, and visitor depends on the treatment plant operating continuously every day, throughout the year, and through all weather conditions,” said Commissioner Mingus Mapps. “These upgrades will help continue reliable service that protects our environment, public health and worker safety. I am pleased that these improvements will protect ratepayer investments by maintaining reliability and increasing efficiency.”

Environmental Services plans to invest more than $400 million in the projects, collectively called the Secondary Treatment Expansion Program (STEP Program). The target completion is 2024. 

Two men on the ground talking to a woman operating heavy equipment.
Environmental Services and its contractors are creating opportunities for women and people of color to build careers in the construction trades.

Construction practices will focus on environmental stewardship, with more than 90 percent of construction waste slated for recycling, the use of green roofs on new structures, more energy-efficient structures and equipment, and other practices. In addition, Environmental Services is working with its contractors to encourage and cultivate a more diverse workforce in the construction trades.

Environmental Services’ project manager is a woman, and the STEP Program is the first in the City with a project-specific Community Benefits Agreement, a contractual strategy aimed at increasing workforce and contracting diversity in City construction projects. 

Workers in an empty aeration basin working on concrete.
The STEP Program will add two new clarifiers and other new construction but also involves repairing existing infrastructure, including the concrete on these aeration basins.

As part of this strategy, the STEP Program is implementing the RISE Up (Respect, Inclusion, Safety and Equity in the Construction Trades) Program to provide workers with the tools and support necessary to create and maintain a safe, inclusive, and productive environment for everyone. Environmental Services, its contractor and members of the community and construction trades meet monthly to review data and provide advice on the employment of women and people of color in apprenticeships, workforce, and subcontracting roles on the projects, and discuss opportunities to further participation as the project progresses.

The main features of the STEP Program are: 

·Seismically-resilient clarifiers. Environmental Services is building two new clarifiers that are deeper and wider than the existing set of eight clarifiers and will be seismically reinforced. These secondary treatment clarifiers add capacity to treat wastewater during storms and are mandated to be completed by 2024 by the Oregon Department of Environmental Quality. 

·Seismically-resilient solids handling building. Wastewater is not just water – and includes nutrient-rich material that is recovered, treated, and then used on eastern Oregon rangelands, helping farmers increase yields while also sequestering carbon. The new solids building will be seismically resilient, have a green roof, be a healthier work place with better ventilation, and have equipment that is more efficient. The equipment will remove at least 30 percent more water from the solids, which will in turn reduce transportation costs and emissions. 

·Aeration basin upgrades. The plant has eight aeration basins that use microorganisms or bugs to break down organic components in wastewater. The basins’ surfaces are being cleaned and restored to extend the life of this essential equipment. This work cannot take place during wet weather when the plant may be at capacity treating combined sewer and stormwater. The work will take place over four summers. 

·Healthier, energy-efficient workspaces. The STEP project will recycle more than 90 percent of construction waste as crews deconstruct older structures and equipment to make space for the new clarifiers and biosolids building. In addition, crews are building a new office building with a maintenance shop that will provide healthier work areas for essential workers and will be built to LEED-Gold standard for environmental and energy efficiency. 

As the project progresses, Environmental Services is developing opportunities for additional environmental and fiscal benefit. For example, the project manager last month brokered an agreement to recycle and reuse soil and excavated material instead of sending it to the landfill. The material will instead be used by the Port of Portland, which received regulatory approvals through the Oregon Department of Environmental Quality for its use. That arrangement repurposes 10,000 cubic yards of excavated material, saves the City $670,000, and reduces climate and air pollution by avoiding emissions from hauling.

Find out more about the STEP Program at


Environmental Services – the City of Portland’s sewer and stormwater utility – operates the Columbia Boulevard Wastewater Treatment Plant, Oregon’s largest, serving a population of more than 600,000.  Through the treatment process, Environmental Services turns 70 million gallons of wastewater into clean water every day while recovering resources that are converted into soil nutrients and renewable energy. During rains, the amount treated can reach up to 450 million gallons daily.



Diane Dulken

Public Information Officer