Portland begins 3-year replacement of 90-year-old Carolina Trunk sewer under I‑5
(UI) — Portland’s Bureau of Environmental Services has begun a multi-year effort to replace the aging Carolina Trunk sewer line, a nearly 90-year-old pipe that runs beneath Southwest Slavin Road and under Interstate 5 to Macadam Avenue.
The $multi-million project will address structural deterioration in the large 3- to 4-foot-wide trunk line, which serves as a key conduit for both sanitary sewage and stormwater. The existing pipe, built on challenging terrain above an old stream bed and landfill, has limited access for maintenance and is increasingly prone to failure.
Crews began major construction in July 2025, using a combination of open-cut excavation and tunneling methods to install new sewer pipes along a revised alignment. The new configuration will shift portions of the system into public rights of way, improving long-term access and reliability.
Construction scope
- Open-cut work: New sewer and stormwater pipes will be installed along Slavin Road, requiring temporary lane closures and retaining walls.
- Tunneling work: Four shafts will be excavated to connect new tunnels under I‑5 and Corbett Avenue, with tie-ins at Macadam Avenue.
- Decommissioning: The deteriorated trunk will be filled with concrete to prevent future issues.
Night work is required near I‑5 to minimize traffic impacts. Temporary barriers, traffic control, and vibration monitoring are being implemented to reduce disruption to nearby residents and property owners. The project is expected to take about three years to complete, with intermittent periods of inactivity.
“The Carolina Trunk runs beneath private property, making traditional repair options nearly impossible,” Environmental Services said in project updates. “This replacement will protect public health, reduce overflow risks, and provide decades of reliable service.”
Residents and businesses will receive regular updates about schedules, closures, and construction impacts via the bureau’s notification system.
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