The Portsmouth Force Main is one of the final projects in the 20-year CSO Program.  The Portsmouth Force Main (PFM) is 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 used a combination of open trench work and microtunneling to construct this segment. All work was on Swan Island.

When using microtunneling to construct large pipelines underground, the contractor installed 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 occured on Swan Island. Construction crews excavated a long deep trench from the ground surface, lowered pipe segments into the trench, and welded them together.

Segment 1 began at the Swan Island Pump Station and extended north through Swan Island to the Basin Avenue cul-de-sac. A microtunnel boring machine constructed the first 3,000 feet of pipe.

Four shafts were constructed along the microtunnel section:

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

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

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

• The Anchor Shaft, was 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 is about 7,000 feet long.

In consideration of the heavy traffic on N Basin Avenue, the open trench construction took place off the road paralleling Basin Avenue and the lagoon until it reached N Ensign Street, where it turned east. The 66-inch pipe was constructed in Ensign to N Basin Avenue, where it continued north to the N Basin Avenue cul-de-sac. 

Segment 2: Willamette Boulevard

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

Services constructed a tunnel under N Willamette Boulevard. 

Environmental Services used a tunnel boring machine (TBM) to construct the deep tunnel. The TBM tunnelled about 100 feet below ground. The 66-inch force main was installed within the tunnel.

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

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

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

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

Force Main North Shaft.

The North 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.