Controlling Combined Sewer Overflows

^{Almost every time it rains, Portland’s combined sewers overflow into the Willamette River. Combined sewer overflows (CSOs) carry raw sewage that pollutes water and threatens our quality of life.}

How We Got Here

^{Older Portland neighborhoods have a sewer system that mixes untreated sewage and stormwater runoff in a single pipe. On rainy days, runoff from buildings, streets, and other hard surfaces fills these combined sewers to capacity and they overflow into the Willamette River.}

When it rains, the combined sewer system fills to capacity

and overflows to the Willamette

Working for Clean Rivers

^{Controlling CSOs is an important part of Portland’s efforts to improve Willamette River water quality. CSO solutions include projects to remove stormwater runoff from sewers and building new facilities to carry sewage and stormwater to the Columbia Boulevard Wastewater Treatment Plant.}

Cornerstone Projects

^{Portland started the CSO control program in 1991 with a set of Cornerstone Projects that remove stormwater from combined sewers. Projects include installing street sumps and sedimentation manholes, building separate sewers for stormwater in some neighborhoods, encouraging homeowners in targeted neighborhoods to disconnect downspouts from the sewer system, and removing west hills streams from the combined sewers.}

Green Solutions

^{Environmental Services promotes other innovative projects to manage stormwater onsite instead of piping it into sewers or streams. Projects include ecoroofs, pervious pavement, swales and stormwater planters.}

Big Pipe Projects

^{Environmental Services completed the Columbia Slough Big Pipe in 2000. The 12-foot diameter pipeline reduced CSOs to the Slough by 99%. Construction of the Swan Island Pump Station and the West Side Big Pipe was completed in 2006. The 3.5-mile, 14-foot diameter tunnel carries combined sewage from the west side of the Willamette to Swan Island, where the Swan Island Pump Station pumps the sewage to to the Columbia Boulevard Wastewater Treatment Plant.}

^{Also in 2006, Environmental Services began construction of the East Side Big Pipe, a six-mile long, 22-foot diameter tunnel to collect sewage from the east side of the Willamette. When the East Side Big Pipe is complete in 2011, CSOs to the Willamette River will be reduced by 94%.}

CSO Milestones

¹⁹⁹³

^{Work begins on project to divert stormwater runoff from the combined sewer system. The sump installation, sewer separation, stream diversion and residential downspout disconnection projects are known collectively as the Cornerstone Projects.}

²⁰⁰⁰

^{Environmental Services completes construction of the Columbia Slough Big Pipe and other slough projects to reduce CSOs to the slough by more than 99%.}

²⁰⁰⁶

^{The 14-foot diameter West Side Big Pipe and Swan Island Pump Station are completed, and work starts on East Side CSO projects.}

²⁰⁰⁷

^{The Downspout Disconnection Program disconnects downspout number 50,000, and disconnections are removing more than one billion gallons of stormwater annually from the combined sewer system.}

Community Benefit Opportunity (CBO) Program

^{In November 2007, the Portland City Council authorized spending $1.77 million on community projects to benefit neighborhoods close to the East Side Big Pipe Project. The city created the Community Benefit Opportunity (CBO) Program to add amenities to neighborhoods affected by CSO construction.}

^{East Side CSO construction affects 11 neighborhoods between SE 17th and McLoughlin Boulevard and Swan Island. Community groups and citizens in those areas nominated 38 projects. A citizens advisory committee reviewed the proposals, and Environmental Services recommended 21 projects for funding.}

^{Projects include bank restoration along the Willamette River, street tree planting, community gardens, and sustainable stormwater management facilities.}

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