Portsmouth Force Main

The City of Portland’s Bureau of Environmental Services entered into a combined sewer overflow abatement agreement with the Oregon Department of Environmental Quality. The final phase of this program is the 3-mile-long (4.8 km) Portsmouth Force Main, which will control the remaining outfalls on the Willamette River. As part of the Brown and Caldwell team, Jacobs Associates performed preliminary and final design.

As part of the preliminary design work, an extensive alignment analysis process was used to arrive at the preferred alternative. In the refinement of the final alternatives, different construction methods were considered. Factors examined in the selection process included operations, risk, constructability, third-party impacts, and costs. A public outreach component was vital to this analysis process and was used to gather input from key stakeholders in the project area and identify traffic concerns for some of the area’s more significant businesses. Because of the extensive input provided by these crucial stakeholders, an additional alignment alternative was identified during this outreach process. This alternative was reviewed and later adopted as part of the preferred alignment, which resulted in lower project costs while minimizing impacts to business and traffic in the most congested portions of the project area.

The project consists of approximately 16,000 feet (4,877 m) of wastewater conveyance comprising 6,000 feet (1,829 m) of conventionally excavated soft ground tunnel, 2,500 feet (762 m) of large-diameter, 84-inch (213 cm) microtunnel, and 7,500 feet (2,286 m) of open-cut construction. Jacobs Associates was responsible for tunnel and trenchless design, shaft design, cost estimating, management of the geotechnical investigation program, and preparation of the Geotechnical Baseline Report.