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About the Big Pipe Project

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Spanning 20 years at a ratepayer investment of $1.4 billion, the Big Pipe Project has reduced combined sewer overflows to the Willamette River by 94 percent and to the Columbia Slough by 99 percent. With most overflows eliminated, the Willamette is cleaner than it’s been in decades.
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The Big Pipe Project is shorthand for an ambitious set of actions and improvements that together eliminated most combined sewer overflows, or CSOs, to the Willamette River and Columbia Slough. Before the Big Pipes, it didn’t take much rain to cause an overflow—only about one-tenth of an inch.

Fast Facts

  • Completed in 2011, the Big Pipe Project took a generation to build – 20 years – and $1.4 billion. 

  • CSOs have been nearly eliminated, dropping by 94 percent to the Willamette and 99 percent to the slough, significantly improving river health.  

  • To eliminate 100 percent of CSOs, the project cost would have doubled without a significant increase in improving river health.  

  • Before Big Pipes, an average of 50 Willamette River overflows occurred each year, sometimes lasting for days. Today, an average of four overflows occur each rainy season and one every third summer. Volume and duration of overflows are also much lower.  

Environmental Services explored several options for controlling CSOs. The option that eliminated most, but not all overflows, was the most cost-effective way to protect our rivers while also recognizing the impact of sewer rates on our customers.

Graphic: 10 Years of the Big Pipe Project. Combined sewer overflows are fewer, shorter, and smaller. Graphic shows three line graphs for number, length, and volume of CSOs. Each shows a steep drop after the 2011 completion of the Big Pipe Project. Average number of overflows drops from 50 to 3.3. Average length drops from 42 to 4 hours. Average volume drops from 6 billion to 297 million gallons.

The Big Pipe Project: More Than Just Pipes

The East Side, West Side, and Columbia Slough Big Pipes are probably the most well-known parts of Portland’s program to control CSOs. The overall program, however, was made up of several projects and initiatives around Portland. 

The Beginning: Cornerstone Projects Divert Stormwater from Sewers 

First were the “Cornerstone Projects.” These were projects to keep stormwater out of the combined sewer system. Each year, these projects continue to keep millions of gallons of stormwater out of sewers.

Downspout Disconnection

The largest of these initiatives was the Downspout Disconnection Program. The City partnered with residents of neighborhoods east of the Willamette River where soils and topography make it safe to disconnect roof drains from combined sewers and redirect the flow to yards or gardens. At the end of the program, more than 56,000 disconnections were keeping 1.2 billion gallons of stormwater per year out of combined sewers. 

Stream Diversion

Environmental Services constructed a pipeline to carry clean stream water, including Tanner Creek, from Portland’s west hills directly to the Willamette River and remove that water from the combined sewer. 

Stormwater Sumps

About 3,000 stormwater sumps and sedimentation manholes in combined sewer areas throughout north, east, and southeast Portland collect street runoff, trap sediment and pollutants, and allow water to soak into the ground. 

Sewer Separation 

Environmental Services constructed new storm sewers in some areas of west, north, and southeast Portland. The largest sewer separation project was in the St. Johns area of north Portland. The project included new storm sewers and a pipeline to convey stormwater to a 26-acre constructed wetland called Ramsey Lake for treatment.

The Big Pipes

The First Big Pipe: Columbia Slough

Environmental Services completed the Columbia Slough Big Pipe in 2000. This 3.5-mile-long tunnel extends from NE 13th Avenue to the Columbia Boulevard Wastewater Treatment Plant. It prevents about 300 million gallons of combined sewage from overflowing into the Columbia Slough each year.

The Second Big Pipe: West Side

Environmental Services completed construction on the West Side Big Pipe in 2006. The 14-foot-diameter, 3.5-mile tunnel extends from SW Clay Street and SW Naito Parkway north to the Swan Island CSO Pump Station.

The Third Big Pipe: East Side

Environmental Services finished work on the East Side Big Pipe project, the largest sewer construction project in Portland history, in 2011. The nearly 6-mile-long tunnel is 22 feet in diameter. Tunneling ended in October 2010, and the city started using the East Side Big Pipe in fall 2011. 

Swan Island CSO Pump Station

The East Side and West Side tunnels meet at the Swan Island CSO Pump Station. As Portland’s largest pump station, it can pump up to 220 million gallons a day through the Peninsular Force Main to the treatment plant.

Treatment Plant Improvements

Adding the Big Pipes to Portland’s sewer and stormwater system brought big changes to the Columbia Boulevard Wastewater Treatment Plant—the City’s main treatment plant. Planning for more water coming to the plant on rainy days, several improvements were needed, including:  

  • New covered dry weather primary clarifiers. The original primary clarifiers are now wet weather clarifiers to treat additional flow on rainy days.
  • A second outfall pipe to carry treated water to the Columbia River. 
  • A facility to remove disinfectant from treated water before discharge to the river. 

Green Infrastructure Works with Big Pipes to Protect the River 

Green streets capture stormwater runoff from streets and sidewalks to keep it out of sewers and to protect the river.

Portland’s green infrastructure — green streets, rain gardens, trees, and more — slow and collect rain and allow it to slowly soak into the ground. By keeping rain out of the sewers, green infrastructure works with the Big Pipes to eliminate CSOs.

Lesley Stahl narrates this 12-minute video about Portland, Oregon's 20-year program to control combined sewer overflows, also known as the Big Pipe Project
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Big Pipes Make a Big Difference

Portland is a leader when it comes to protecting our rivers. Around the country, more than 800 cities like us have combined sewers. Many of them are still designing or constructing systems to solve their CSO problems. In Portland, we've been enjoying our healthier river for a decade.

But, after such a big investment, some ratepayers may wonder why we still have any CSOs at all?  

Stopping all CSOs would have cost at least twice the $1.4 billion that Portland sewer ratepayers invested in the project. This would have resulted in much higher sewer rates for decades and higher system maintenance and operation costs. For double the price tag, we would not have significantly improved river health.  

Today, about a third of a ratepayer’s sewer bill goes to paying debt service on construction of the Big Pipes. Spreading the cost over decades means that everyone who benefits from and uses the new system—from past users to current residents to tomorrow's new residents—helps pay for it.