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The City of Portland, Oregon

Environmental Services

working for clean rivers

Phone: 503-823-7740

Fax: 503-823-6995

1120 SW 5th Ave, Suite 613, Portland, OR 97204

More Contact Info

Does Portland still have combined sewer overflows?

Yes. But they are rare. It takes exceptionally heavy rain to trigger an overflow.

You can check for current CSO (combined sewer overflow) alerts on Environmental Services’  homepage as well as at and 503-823-2479.

Portland’s history of eliminating sewage discharges to the Willamette River

Before 1952 – Before the city built the Columbia Boulevard Wastewater Treatment Plant in 1952, sewage drained directly to the Willamette River and Columbia Slough

After 1952 – Portland's wastewater treatment plant improved water quality. But because the central city and other older areas of the city are served by wastewater pipes that combined sewage and stormwater, even moderate rains would fill the pipes, leading to an overflow. Those overflows are known as combined sewer overflows (CSOs).

Beginning in 1991 – Before the start of Portland’s 20-year CSO control program in 1991, there were an average of 50 overflows a year, some lasting for days. The project to control those overflows would become known as the Big Pipe Project.

December 2011 – Portland completed the Big Pipe Project in December 2011.  The improvements eliminate 94% of combined sewer overflows to the Willamette River and 99% to the Columbia Slough.

Now – With the Big Pipe Project complete, Environmental Services continues to make improvements to Portland's sewer and stormwater system to protect public health and our environment. In addition to replacing and upgrading aging pipes and other 'gray' infrastructure  Environmental Services installs and maintains green infrastructure -  green streets, ecoroofs, trees, and natural areas to absorb stormwater, protect water quality and improve watershed health. 

What about eliminating 100% of overflows?

Eliminating 100% of overflows would have doubled the $1.4 billion cost of the Big Pipe Project without significantly improving river health, according to city projections that were reviewed by the state Department of Environmental Quality and federal Environmental Protection Agency.

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