City to upgrade 'worn-out' Marylhurst pumping station
It's easy for passersby to miss the Marylhurst pump station next to the Old River Road trail; the above-ground portion of the station only consists of a hatch and a nondescript, 4-foot-tall metal box, just north of the point where the trail merges with Old River Road.
But 27 feet below, a group of pumps moves sewage from the Marylhurst area uphill toward George Rogers Park, where the pipe connects to another sewer main that continues on to the Tryon Creek Wastewater treatment plant. The station serves a 347-acre area that includes Marylhurst University and around 1,200 houses.
At maximum capacity, it can pump 1,100 gallons per minute.
But the underground design makes the station flood-prone and difficult to maintain, officials say, which is why a $1.89 million project is in the works to replace it with a modern design that will keep the pipes underground but relocate much of the electrical and control infrastructure to the surface.
"It's old and worn out," says Project Manager Pat McDougal, a Lake Oswego engineer. "It's fairly difficult to get equipment in and out of there, and the people to maintain it. Plus it's below the floodplain."
The station is the second largest of the handful of municipal pumping stations in Lake Oswego, McDougal says, and it's the oldest still in operation — it was built in 1981, while most of the others were built or upgraded in the past 10-20 years.
Relocating parts of the station to the surface will allow easy access for future monitoring and maintenance needs, McDougal says. It will also allow for the installation of "smart pumps" that are more efficient and can automatically adjust their motor speed to save power when the flow rate is lower than usual.
Most importantly, McDougal says, the project will add an on-site backup generator to reduce the flooding and jam-ups that have plagued the existing system. There's no space for a generator at the bottom of the current pit, McDougal says, so the pumps stop working every time the power goes out. As a result, the station has overflowed eight times in the past 10 years.
"It can overflow within 20 minutes of losing power," he says.
The surface part of the station will need to be housed inside a small utility building next to the path, and Lake Oswego city staff and project consultants have been seeking public input about the design. The location and shape are determined by the project needs, but visitors at a recent open house were asked to weigh in on the materials and colors for the walls and roof.
"It's basically trying to blend it in and making it a little more park-like," says consultant Mike Faha of the architecture firm Greenworks PC.
The area around the station building will be designed as a small park space with benches for walkers to use and a hard surface that will reuse some of the existing station's surrounding paver tiles, signs and boulders.
Project staff say they did look into the possibility of moving the station somewhere less obtrusive, but found that any alternate location would substantially raise the project's cost because the Marylhurst neighborhood's underground network of sewer pipes was built out with the station as the convergence point.
"Anywhere we move this, we'd have to re-pipe all of the (incoming) lines," says consultant Adam Crafts from the firm Murraysmith, "and this is solid rock in this area."
Construction is expected to begin in late 2018 or early 2019 and last for four to six months. No disruptions to sewer service are expected during the project.
Project staff say the adjacent portion of Old River Road will need to be closed to non-emergency traffic for a majority of that time, which will result in some nearby residents having to take a longer detour around the Marylhurst University campus.
However, officials say they plan to keep the Old River Road pathway open throughout the construction period because it sees much more traffic than its roadway counterpart, and there isn't a convenient alternative route for walkers and bikers.
The new structure is expected to have a greater longevity than its predecessor, officials said. The pumping units need to be replaced every 20 years, but the above-ground station will make that process easier, and the overall building will last 75-100 years.