Underground tunnel from Ballard to Wallingford will benefit Ship Canal

An underground tunnel project aimed at keeping pollution out of Puget Sound has reached its half-way mark to completion. 

The underground sewage tunnel from Ballard to Wallingford will eventually measure 2.7 miles long and 19 feet in diameter. When completed, the tunnel will be large enough to store up to 30 million gallons of sewage and stormwater runoff during heavy rains, according to the Ship Canal Water Quality Project, which falls under Seattle Public Utilities. 

"So what it’s going to do is, it’s going to hold that sewage and that polluted stormwater in the tunnel rather than discharging it, which will impact the water quality of the Ship Canal," said Keith Ward, the project executive of the Ship Canal Water Quality Project. "And when the storm is over, will turn on a 12 million gallon pump station and pump it to the West Point Treatment Plant."

Ward said that it's not just the Ship Canal, but Lake Union and the entire Puget Sound will be spared contamination when Seattle's aging sewage system gets overwhelmed by runoff. 

Officials say the $570 million project is already over budget before it even reached completion due to COVID delays and having to work around a massive boulder. 

Because of this, the project is about eight to 10 months behind schedule, Ward said. The date of completion is expected to extend beyond its original date of 2025.

Cost is also a concern: the price tag could grow an additional 10% or more when done, but at this point, the overrun should not result in any extra costs for utility customers, who are already facing annual increases through 2026.

The daily dig target is 65 new feet of progress. A revised completion date is expected for the whole project to be presented this summer.