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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

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CSO tunnels are among the nation's top engineering projects

The American Society of Civil Engineers (ASCE) has recognized Portland's Willamette River CSO Tunnel Program as one of the top engineering projects in the country. The Portland program is one of five finalists for the 2012 Outstanding Civil Engineering Achievement (OCEA) Award.

Each year, the ASCE recognizes a project that best illustrates superior civil engineering skills and significantly contributes to civil engineering progress and society.The ASCE will announce the overall winner at its annual award ceremony in Washington, D.C. next March.

"I'm proud of how we implemented the CSO tunnel program," said Dan Saltzman, the Portland City Commissioner in charge of Portland Bureau of Environmental Services. "The only way that this enormously complex program could be successful was through excellent management, and that is exactly what Environmental Services delivered," Saltzman said.

The Willamette River CSO Tunnel Program is a major part of Portland's 20-year program to control combined sewer overflows (CSOs) to the Willamette River and Columbia Slough. The work consisted of constructing tunnels on both sides of the Willamette River, several tunnel shafts and connecting pipelines, two pressure sewers and a large pump station.

The city activated the West Side CSO Tunnel (West Side Big Pipe) and the Swan Island CSO Pump Station in 2006. Two tunnel boring machines working at depths ranging from 100 feet to 150 feet constructed the 3.5-mile long, 14-foot diameter tunnel. Because tunneling was in variable ground conditions well below the water table, Portland used what are known as slurry pressure tunnel boring machines. It was the first use of this kind of machine in the United States.

The city also used a slurry pressure tunnel boring machine to construct the six-mile long, 22-foot diameter East Side CSO Tunnel (East Side Big Pipe). The city finished east side tunnel construction in October 2010, installed additional pumps at the Swan Island CSO Pump Station this summer, and is in the process of activating the tunnel.

An innovative contracting method developed specifically for the tunnel projects was instrumental in the city completing both the $293-million West Side Tunnel Project and the $426-million East Side Tunnel Project ahead of schedule and under budget.

Because of the specialized expertise and equipment required for the work, the city hired prime contractors based on qualifications rather than using the conventional low-bid process.

The construction contracts used a cost-reimbursable, fixed fee structure. Submitting a fixed fee through a competitive process and estimating reimbursable costs up front fostered closer teamwork between the city and project contractors and designers. This contracting method is now known in the tunneling industry as the Portland Method.

The successful management of this program has also contributed to the Bureau of Environmental Services' favorable revenue bond rating, which is higher now than when CSO tunnel construction began.

Completing the tunnel program will have a positive impact on Willamette River water quality. When the city finishes CSO construction this fall, combined sewer overflows to the river will drop from an average of 50 a year to an average of four per winter and one every three summers during very heavy rain events.

For more information contact Linc Mann, 503-823-5328