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About the Secondary Treatment Expansion Program

Aerial photo from 1974 of the Columbia Boulevard Wastewater Treatment Plant. About half the plant is outlined to show what areas are being impacted by the STEP program.
STEP is the largest improvement project at the treatment plant since the 1970s. The improvements will increase the plant's resiliency, protect water quality, and provide healthier work environments for essential workers.
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Project Overview

The two main features of the project are two new clarifiers that will increase the plant’s secondary treatment capacity and new solids processing facilities to replace old assets and increase capacity to year 2045. The clarifiers will take the place of old composters and work buildings along the Columbia Slough. As with any project on a complex campus, construction in one area will impact areas nearby.This will be particularly challenging as new clarifiers and equipment are connected to existing treatment processes, which will need to keep operating 24/7 as this work occurs.   

Aerial photo of wastewater treament plant with 4 areas marked. Work zone E in northeast corner; Work zone C middle north; Work zone S adjacent west of C; Work zone A along western boundary of campus; Work zone T in the northwest corner. The Columbia Slough is to the northand N Columbia Boulevard to the south.

Primary Work Areas

Most changes will occur on the plant campus, but the neighborhoods nearby may see cranes, equipment coming into the plant, and other construction activity. Temporary facilities are installed near the construction entrance to house construction, engineering, and operations staff until the new building is available in the future. Environmental Services is committed to providing information and opportunities to learn more as we move forward with this important work.

Work Area A: Aeration Basins

There are eight aeration basins that use microorganisms to break down organic components in wastewater. These basins have been operating since the early 1970s. The concrete and joints show signs of wear. The concrete will be cleaned, and the surface restored to extend the life of the basins. The plant can operate with two tanks out of service during the summer. This work will take place over four summers.

Work Area C: Clarifiers

Clarifiers are large tanks in which aerated wastewater slows down and solids from this process separate from the water. Large tanks are essential to provide enough space to clarify the water before it goes to final disinfection. Two new deeper, larger clarifiers will be added to increase the biological treatment process capacity.

Work Area E: East Pad

To make room for the new clarifiers, several aging work areas will come down and some storage facilities nearby will be renovated. A new multi-use building will be constructed to house staff, shops, and increase storage space. There will also be a new large, three-walled, sheltered storage space in this area.

Work Area S: Solids Facility

Solids handling facilities are a critical part of the treatment process. Clarified biological solids from clarifiers get thickened and sent to big digestion facilities. In the digesters, microorganisms reduce the solids volume and produce biogas. These solids are very wet, but rich in nutrients. They return to the solids handling facility to remove excess water. These facilities date back to the 1970s and operate 24/7. The facilities and the process need to be replaced with more effective technologies. Capacity needs to increase to keep up with the population growth in Portland.

Work Area T: Tunnels

Tunnels provide access to equipment and pipes underground. This allows workers to maintain and operate the clarifiers and other parts of the plant. New pipes will be added. These will connect the new clarifiers with the aeration basins and existing clarifiers. New electrical equipment above ground will replace old equipment currently located in the tunnels where it is at risk from possible flooding, which could cause a catastrophic failure of the plant.  

Project Background

The Columbia Boulevard Wastewater Treatment Plant is essential to protecting the health of our community and our region's rivers and streams. The plant serves all Portlanders, every hour of every day.

The plant is closely regulated by federal and state authorities. In 2011, when Portland completed the Big Pipe Project to eliminate nearly all combined sewer overflows, the City signed an agreement with the Oregon Department of Environmental Quality on how to treat the increase of wastewater now going to the plant during heavy rains. STEP is the final obligation in that agreement. The additional secondary clarifiers will give plant operators more options for how to process that increased flow and provide more biological treatment during heavy rainfalls. This requirement must be met by 2024. 

With the need to add the clarifiers, the program includes other planned and needed improvements. Most of the facilities that are part of the STEP project were built in the 1970s. That's when Portland expanded the plant to add secondary treatment. After nearly 50 years of continuous service, these facilities are growing old and need to be updated or replaced. Improvements will help the plant continue to protect public health, water quality, and the environment while also providing healthier work environments for our essential workers.

Aerial photo from 1974 of the Columbia Boulevard Wastewater Treatment Plant. About half the plant is outlined to show what areas are being impacted by the STEP program.
This 1974 photo shows the secondary treatment expansion at the plant. STEP projects will improve or replace many facilities built at that time.

STEP Provides Contracting and Workforce Diversity Opportunities

In October 2017, City Council approved a Construction Manager/General Contractor (CM/GC) approach to manage the project. This helps Environmental Services minimize construction risks while working to meet the mandated deadline. The CM/GC approach also provides opportunities for increasing equity and diversity on the project team through contracting with locally certified businesses and apprentice programs for women and people of color in the construction phase. As part of these efforts, the CM/GC is committed to follow the Rise Up respectful workplace campaign to shift the culture of construction to be more inclusive to a diverse workforce.

Sign Up for Updates

Sign up for periodic email or text message updates for the Secondary Treatment Expansion Program through our free GovDelivery subscription service. These updates are the best way to stay informed about what’s happening and what to expect. You can also sign up for bulletins on other projects and topics. 

This project will help protect the health of the Columbia Slough Watershed.