Construction has begun on the Portsmouth Force Main, one of the final projects in the 20-year CSO Program.  The Portsmouth Force Main (PFM) will be a 66-inch diameter, three mile long pressurized pipeline that will carry combined stormwater and sewage from the Swan Island Pump Station to the existing Potsmouth Tunnel.  The tunnel will carry combined flows by gravity to the Columbia Boulevard Wastewater Treatment Plant.

The Swan Island facility currently pumps up to 100 million gallons a day through the Peninsular Force Main.  The Portsmouth Force Main will carry up to an additional 120 million gallons per day when it's complete in 2011.

Construction in Two Segments

Segment 1: Swan Island

Environmental Services will use a combination of open trench work and microtunneling to construct this segment. All work will be on Swan Island.

When using microtunneling to construct large pipelines underground, the contractor will install shafts along the pipe alignment to either launch the remote-controlled microtunnel boring machine (MTBM) or to remove the machine. The pipe sections are pushed behind the MTBM as it advances. The operator controls the machine from a control room aboveground. MTBMs are similar to, but much smaller than, the tunnel boring machines used to construct the Big Pipes.

Open trench construction will occur on Swan Island. Construction crews will excavate a long deep trench from the ground surface, lower pipe segments into the trench, and weld them together.

Segment 1 begins at the Swan Island Pump Station and extends north through Swan Island to the Basin Avenue cul-de-sac. Amicrotunnel boring machine will construct the first 3,000 feet of pipe.

Four shafts will be constructed along the microtunnel section:

• The Swan Island Pump Station Shaft, located outside the public right-of-way at the Swan Island Pump Station

• The Port Center Shaft, located in the corner of the FedEx Parking lot off the N Port Center Way cul-de-sac

• The Going Street Shaft, located in the landscape median of N Going and Basin avenues

• The Anchor Shaft, located in the parking lot of a business complex at 3449-3627 N Anchor Way

The Anchor Shaft is where microtunneling ends and open cut construction begins. The open cut portion of the alignment will be about 7,000 feet long.

In consideration of the heavy traffic on N Basin Avenue, the open trench construction will take place off the road paralleling Basin Avenue and the lagoon until it reaches N Ensign Street, where it turns east. The 66-inch pipe will be constructed in Ensign to N Basin Avenue, where it will continue north to the N Basin Avenue cul-de-sac.  The boat ramp will remain open during construction.

Segment 2: Willamette Boulevard

Construction of this segment will use both open trench and deep tunnel construction. Environmental

Services is constructing a tunnel under N Willamette Boulevard. There will be construction activity at the surface on Swan Island and the bluff.

Environmental Services is using a tunnel boring machine (TBM) to construct the deep tunnel. The TBM will tunnel about 100 feet below ground. The 66-inch force main will be installed within the tunnel.

Segment 2 includes a short portion of open trench construction in the N Basin Avenue cul-de-sac on

Swan Island leading to the South Portal Shaft just outside of the cul-de-sac. Deep tunneling will begin

at the toe of the Willamette bluff at the South Shaft and continue north 6,000 feet under N Willamette

Boulevard to N Carey Avenue where it will connect to the existing Portsmouth Tunnel at the Portsmouth

Force Main North Shaft.

The North Portal Shaft is located on property currently occupied by the Willamette Boulevard Service

Center. Construction of the shaft required the permanent relocation of Golden Harvesters, the food co-op previously located on the property.

Odor Control Measures

It is unlikely that any sewer odors will be generated at the North Portal Shaft. But because it is possible under some operating conditions, the project includes installation of odor control equipment in two locations.

Environmental Services will install equipment to chemically treat the combined sewage flow at the Swan Island CSO Pump Station, and will also install equipment at the North Portal Shaft to control any odors generated at the connection to the Portsmouth Tunnel. The design of the pump station’s chemical injection system is underway, and Environmental Services recently issued a request for proposals for a consultant to work on design of the odor control system at the North Portal Shaft.

Environmental Services will hire the consultant this April. Design is scheduled to begin this June and will be complete by this December. Environmental Services will schedule public meetings and attend neighborhood and business associations meetings to gather input.  Project updates will be emailed and mailed to keep the public informed during the design process.