As part of what is believed to be the city of Portland, Ore.'s largest construction effort in history, work began in 2003 on a $260 million sewer tunneling project along the west side of downtown and under the south-to-north-flowing Willamette River. The work is part of the city's state-mandated $1 billion, 20-year combined sewer overflow program, aimed at curtailing Willamette River and Columbia Slough pollution during rainstorms.

In December 2003, production began on the project's first 84-in. jacking pipe at the Hanson Pipe & Products plant in Tualatin, about 15 miles southwest of downtown Portland. With installation of the pipe beginning in March, Hanson's work on this endeavor is scheduled to be completed in February 2005 with the producer contributing nearly 3,000 ft. of 84-in. pipe and more than 5,800 ft. of 72-in. jack pipe. The latter is earmarked for a secondary part of the project called the Southwest Parallel Interceptor, which feeds the larger West Side Big Pipe project. The entire tunnel project should be completed sometime in 2006.

Portland's Bureau of Environmental Services selected the joint venture of Impreglio/S.A. Healy as the contractor on the project, which involves tunneling under Tom McCall Waterfront Park, burrowing under the Willamette and building a sewage pump station to send westside sewage to the city's wastewater treatment plant on North Columbia Blvd. Built 150 ft. below ground, the new pump station on Swan Island will process 220 million gallons per day and occupy as much area as a 15-story downtown landmark, The Portland Building.

The West Side Big Pipe tunnel will be 3.5 miles long and 14 to 15 ft. in diameter. The contractor is using two large tunnel boring machines (nicknamed Lewis and Clark) to build the tunnel at depths ranging from 120 to 150 ft. Environmental Services will build a pressure line called the Peninsular Force Main to move sewage from the Swan Island Pump Station to an existing tunnel near North Greeley Street and North Going Street. The 5,000-ft.-long force main will consist of two parallel pipes with diameters of 30 in. and 48 in. The bureau is also constructing five large shafts along the West Side Big Pipe alignment. The shafts are located at points where sewage flows into the tunnels and will allow maintenance crews and equipment to access the tunnel. During construction, the shafts are being used to lower equipment into the tunnel and to inspect and repair the boring machines.

The 20-year program is designed to reduce combined sewer overflows (CSOs) to the Columbia Slough and Willamette River. Projects to date have eliminated almost all CSOs to the Columbia, and have reduced total CSO volume by more than 3 billion gallons a year. Construction of major Portland-area CSO projects (including a 6-mile tunnel project along the east side of the river) will continue through 2011.

THREE-TIERED SOLUTION

The city of Portland began to deal with its CSO issues in 1991 when the state of Oregon placed it under an amended, stipulated final order to improve the situation substantially. The city immediately instituted a three-tiered approach to its sewer situation. While sewer infrastructure plans were being made, initial cornerstone projects were announced whose goal was to simply remove as much excess stormwater as possible from the community. Household downspouts connected directly to the sewers were disconnected. Many homeowners installed sumps. A stream diversion project was implemented And in some of the smaller neighborhoods, homes were separated from their smaller sewer systems and linked to larger, existing ones.

Tier 2 included cleaning up the Columbia Slough, recognized as the most polluted waterway in the state. Compared to the West Side Big Pipe project, this smaller fix included the installation of about 3.5 miles of 6- and 12-ft. pipes and the expansion of the Columbia Blvd. Wastewater Treatment plant.

The pipe projects on either side of the Willamette River and the building of the massive Swan Island pump station make up the work in the Tier 3 projects.

To create the West Side Big Pipe, 5-ft.-wide curved precast sections making up the outer wall of the tunnel are placed as part of the boring process. Five of these segments comprise a ring measuring 15-ft. in diameter.

PAYING THE PRICE

Although CSO projects have progressed in many communities for years, the Environmental Protection Agency's Combined Sewer Overflow Control Policy was added to the Clean Water Act (CWA) in 1994 in an effort to mandate the upgrading of combined sewer systems (CSS). Many of these wastewater collection systems conveying water through a single-pipe system to a treatment facility were among the nation's earliest built wastewater infrastrucutres and often overflowed during “urban wet weather” situations such as rainfall or heavy snowmelt.

The CWA establishes national goals and requirements for maintaining and restoring the nation's waters. As point sources, CSOs are subject to the technology- and water quality-based requirements of CWA. CSO systems have been identified in upwards of 770 communities across 32 states (including Washington, D.C.). Approximately 30 percent of these communities have populations greater than 75,000, while an additional 30 percent have less than 10,000. CSO communities are using a combination of local funding sources, Clean Water State Revolving Fund loans, state grants and loans, and, in special cases, line item congressional appropriations to fund CSO controls. Most of these communities are located in the Northeast, Great Lakes or Pacific Northwest regions. The Portland overhaul, paid for entirely by residents who use it via a sewer rate payment, is typical of other major city overhauls, including work done in Seattle, San Francisco, Boston, Detroit, Chicago, Cleveland, Philadelphia, Newark and New York City.

SW PARALLEL INTERCEPTOR

For Hanson Pipe, specifications for the pipe joints on the 3-mile Southwest Parallel Interceptor project included a zinc-coated steel bell on the jacking pipe in place of a typical concrete bell. In addition to a confined O-ring gasket on the exterior of the spigot, the specs also called for a second gasket to provide a seal between the spigot end and the inside concrete surface at the bell, located adjacent to the steel bell band. The second gasket is designed to protect the steel bell band from environmental conditions inside the pipe when operational.

D-load testing of Hanson's 72- and 84-in.-diameter pipes is performed in accordance with Section 5.1.1 of ASTM C76 and Section 4 of ASTM C497. Acceptability is based on the results of the three edge-bearing tests for the load to produce a 0.01-in. crack and the ultimate strength of the pipe.

Pipe joint sheer tests are performed in accordance with American Concrete Pipe Association standard guidelines, plus an additional 50 percent externally applied loading. Upon removal of the test load and the disassembly of the joint, neither the bell nor the spigot can show permanent deformation or damage other than hairline cracks of 0.01 in. or less.

The Southwest Interceptor pipeline will meet the main West Side CSO Tunnel at SW Clay Street at the Clay Shaft. A microtunneling boring machine, nicknamed “Sacagawea” was lowered into a the tunnel in mid-March.

Contractors hope that construction on the East Side phase of this project can begin right as the West Side Big Pipe wraps up construction in 2006.