To repair and replace its aging sewer system, the City of Portland Office of Environmental Services has several programs running concurrently, including a Small Bore Program, a Downtown–Old Town Tailored Program, and the Large Bore Program (36 inches plus), which includes the Carolina Trunk Replacement. Some of the pipes date back to the early 1800s; about a third of the city’s sewer lines are more than 80 years old. On average, the city spends between $30 million and $50 million annually on rehabilitation programs, funded by BES taxpayers.
While the Carolina project is the largest to date, there are several other major projects currently in the design phase. “Right now, the large-diameter program is targeting some of our brick sewers, where we’ve seen failures,” says Amy Dunning, BES engineering supervisor. Inspectors usually use CCTV to analyze pipe conditions, although BES has piloted some drone inspections. “Making sure we’re getting a signal is the biggest challenge with drone inspections, but I expect the technology to move forward and improve.”
As with the Carolina project, many other trunk lines have unique obstacles to overcome, including some older brick pipes and lines that are not circular. “We have an egg-shaped sewer that we’re tackling right now” that’s about 42 inches. x 79 inches, says Dunning. The shape provides an “extra special challenge when it comes to rehabilitation,” which will likely use site-cured pipes.
Many of the trunk lines are in much flatter areas than the steep slopes of the Carolina site. The recently completed Stark trunk rehabilitation project, for example, used a spiral wound liner as a seismically resistant solution, as the project was located near the Willamette River, where soil conditions are softer and more liquefiable.
The agency has a strong team to meet the challenges. “We have in-house construction management, inspection, safety and public engagement teams that are used to delivering this type of work, and it’s very helpful for us to have these in-house resources to make sure we’re getting the best value for the citizens of Portland,” says BES Engineering Supervisor Ryan Carney.
Looking for quick answers on construction and engineering topics?
Try Ask ENR, our new intelligent AI search tool.
Ask ENR →
