by Sara 

Major sewage pipeline project begins


Construction on a new sewer pipeline into Magnolia has begun. Map courtesy of the King County Department of Natural Resources and Parks.?

Nestled deep down in the muck at the bottom of Salmon Bay are two large wooden pipes that carry more than 60 million gallons of sewage every day from Ballard to the West Point Waste Water Treatment Plant in Discovery Park.
Those pipes are 80 years old and leaching. So King County?s Department of Natural Resources and Parks (DNRP) is replacing them in a two-part project. The DNRP will replace the old pipes by nesting plastic pipes inside each of them. And in anticipation of more demand on the system over the next several decades, the department will add a third pipe by digging a tunnel well beneath Salmon Bay.

The original wooden-stave sewage pipe was built in 1935. Photo courtesy of the Department of Streets and Sewers Photographs

The department is demolishing a small warehouse at Shilshole Avenue Northwest and Northwest 20th Avenue to make room for a staging area of the $48.8-million project. At that staging area, crews will dig a hole about 120-feet deep, and do the same on the Magnolia side. Then a tunnel-boring machine will be put in the hole where it will bore out the pipe corridor 120 feet under the bay. The new pipe will be 84-inches wide, and, combined with the new twin pipes, is expected to handle community sewage through this century. The wooden pipes currently transport more than 60-million gallons of sewage every day.

A cross-section of Salmon Bay shows the path of the new pipeline. Diagram courtesy of King County Department of Natural Resources and Parks.?

An algorithm the county uses to project job creation cites that for every $10 million that the county spends on projects, there are about 140 full- and part-time jobs created. That works out to be 672 jobs to build the new sewer system.
To pay for the project, the county accepted a $10-million loan from the Washington State Public Works Board. The loan is at 0.5-percent interest over 20 years. The State Department of Ecology is also loaning the county $31,850,000 for construction costs. The county?s Wastewater Treatment Division has also secured a bond for $7,030,500 to pay for the rest of the project.

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  1. I hope Surf Ballard shares the story about raw sewage leaching out of pipes in Salmon Bay. Now people really want to stay on the board when they try stand up paddling.

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