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Environmental Services

working for clean rivers

Phone: 503-823-7740

Fax: 503-823-6995

1120 SW 5th Avenue, Room 1000, Portland, OR 97204

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Combined Sewer Overflow Control

CSO volume reductions

Portland completed combined sewer overflow (CSO) program construction in 2011 to reduce CSOs to the Columbia Slough by more than 99% and to the Willamette River by 94%.
Before CSO control: An average of 50 Willamette River CSO events each year.
Today: An average of four CSO events each winter and one event every third summer.

CSO videoLesley Stahl narrates Portland's CSO Program, a video overview of Portland's 20-year program to control combined sewer overflows.

downspout disconnectionCornerstone projects - downspout disconnections, sumps, stream diversions and sewer separations - removed millions of gallons of stormwater from combined sewers to allow construction of smaller CSO control facilities.

big pipe constructionBig Pipes - one on the Columbia Slough, two on the Willamette River - intercept combined sewage and stormwater and direct it to the treatment plant.





Watch "Portland CSO Program 1991-2011"

Video overview of Portland's 20-year combined sewer overflow control program

Cornerstone Projects

Downspout disconnection, sump installation, stream diversion and sewer separation are cornerstones of CSO control

Big Pipes

CSO control tunnels on the Columbia Slough and Willamette River

River Alert

See if a combined sewer overflow (CSO) or sanitary sewer overflow (SSO) advisory is in effect

Green Infrastructure

Green infrastructure and grey infrastucture work together to prevent sewage overflows