By rosebell
Commissioned by Seattle Public Utilities through a partnership between the City of Seattle and King County, the project will reduce discharges of untreated sewage and polluted stormwater into the Lake Washington Ship Canal, Salmon Bay and Lake Union.
The scheme addresses capacity constraints in Seattle’s historic combined sewer system, which can become overwhelmed during heavy rainfall.
4.3km tunnel provides 112 million litres of storage
The project centres on a 4.3km-long tunnel with an internal diameter of 5.7m. It can temporarily store approximately 112 million litres of combined sewage and stormwater during periods of heavy rainfall.
The captured flows can then be transferred to a treatment facility when sufficient capacity becomes available, reducing the volume of untreated wastewater discharged into surrounding waterways.
The system serves urban areas including Ballard, Fremont, Wallingford and Queen Anne, where stormwater and sewage share sections of the existing drainage network.
According to Lane, the completed project is expected to prevent up to 284 million litres of polluted stormwater and sewage from entering local waterways annually, helping improve water quality and protect aquatic ecosystems.
Herrenknecht EPBM excavated beneath Seattle
Tunnel excavation was carried out using MudHoney, a Herrenknecht earth pressure balance machine (EPBM) with an excavation diameter of approximately 6.7m.
Manufactured in Germany and assembled in Seattle in 2021, the TBM excavated beneath densely developed urban areas to construct the underground storage infrastructure.
The completed tunnel increases the capacity of Seattle’s wastewater network to manage excess flows during storm events, strengthening the resilience of the city’s drainage infrastructure.
Lane expands US tunnelling portfolio
The Ship Canal Water Quality Project adds to the tunnelling portfolio of Lane and its parent company, Webuild Group, which includes more than 160km of tunnels constructed across major US metropolitan areas.
Other projects in the group’s US portfolio include the Ohio River Tunnel in Pennsylvania and the Palisades Tunnel in New Jersey.
