The city began work on the CSO Facilities Planning Project in 1991, and began construction on the Cornerstone Projects in 1993. The projects included sewer separation, stormwater sump installation, downspout disconnection and stream diversion. The completed Cornerstone Projects divert more than two billion gallons of stormwater annually from the combined sewer system. The total cost for Cornerstone Projects was about $146 million.
Environmental Services eliminated combined sewers in key neighborhoods by installing new pipes to separate stormwater from sewage.
Environmental Services installed about 3,000 stormwater sumps and sedimentation manholes in combined sewer areas throughout north, east and southeast Portland. Residential street runoff flows into manholes that trap sediment and pollutants. The stormwater then flows into sumps and soaks into the ground.
The city worked with owners of residential, multifamily and small commercial properties in combined sewer areas east of the Willamette River to disconnect downspouts from the sewer system and redirect roof water to yards and landscaping. Downspouts were disconnected at more than 56,000 properties, removing more than 1.2-billion gallons of stormwater per year from the combined sewer system. Click here to learn more about the Downspout Disconnection Program.
In 2006, Environmental Services completed construction of a pipeline that diverts Tanner Creek and smaller west hills streams from the combined sewer system. The City piped creeks into the sewer system decades ago to make way for development. The completed Tanner Creek project removes about 165-million gallons of stormwater annually from the combined sewer system.