Photo by Jessica Keller: The Ship Canal Trail, which runs through north Queen Anne, past Seattle Pacific University, is popular with both bikers and pedestrians. During an upcoming Seattle Public Utilities wastewater pipe installation project, a small section of the trail will be closed off through 2023.
Photo by Jessica Keller: The Ship Canal Trail, which runs through north Queen Anne, past Seattle Pacific University, is popular with both bikers and pedestrians. During an upcoming Seattle Public Utilities wastewater pipe installation project, a small section of the trail will be closed off through 2023.

Starting this month, Seattle Public Utilities will begin construction on a three-year project in north Queen Anne that will feed into a larger project to improve water quality in Seattle’s Ship Canal.

According to the Ship Canal Water Quality Project website, , the project is a cooperative effort between SPU and King County Wastewater Treatment Division to build an underground storage tunnel to “significantly reduce the amount of polluted stormwater (from rain) and sewage that flows into the Lake Washington Ship Canal, Salmon Bay and Lake Union from our sewer system during storms.”

The 18-foot, 10-inch wide storage tunnel will hold more than 29 million gallons of untreated stormwater and sewage from six different overflow pipes and temporarily store it until the county’s wastewater treatment plant in Magnolia is ready to manage it. The storage tunnel will be 2.7 miles long and run from Ballard to Wallingford.

Preparation work for Queen Anne’s section of the project will begin this month and conclude in 2023. According to the project outline, work will take place near the West Ewing mini park, and a portion of the Ship Canal Trail, which runs behind Seattle Pacific University and parallel to West Nickerson Street, will be rerouted until 2023.

Preliminary work entails installing wheel stops and bollards (to control road traffic and prevent damage from accidents); removing trees onsite; and installing stormwater control and soil monitoring equipment.

Workers will then build a new tunnel, 8 feet in diameter, under the Ship Canal that will carry stormwater and sewage flows from Queen Anne to Fremont. From there, flows will be able to travel into the storage tunnel before being sent to be treated at King County’s Wastewater Treatment Plant in Magnolia. According to the project outline, workers at Queen Anne’s site will also build a 75-foot, 20-feet in diameter vertical drop shaft to direct the flows into the new tunnel; and install new pipes to convey polluted stormwater and sewage to the drop shaft.  At the end of the project, workers will restore impacted areas to previous conditions, including replanting trees and repaving streets.

In some Seattle neighborhoods, sewer pipes also carry untreated stormwater from roofs, drains and streets. During a heavy storm, excess sewage and stormwater that exceeds the wastewater system’s capacity overflows into nearby bodies of water and can harm fish, wildlife and swimmers. Combined sewer overflows in Ballard, Fremont, Queen Anne and Wallingford send sewage and stormwater into the ship canal 130 times per year on average, according to the Ship Canal Water Quality Project.  In 2018, 84 percent of the city’s overflows came from the combined sewers in Crown Hill, Ballard, Fremont, Wallingford, Queen Anne, downtown and Capitol Hill.

During construction, residents can expect: construction-related noise, traffic, dust and vibrations; increased truck traffic along West Nickerson and Third Avenue West; parking restrictions and roadway detours. Visit https://spushipcanal.participate.online/ for more information.