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Crews respond to non-toxic construction clay spill near Lake Sammamish


A King County sewer utility contractor working on a pipeline construction project near Lake Sammamish in Bellevue reported a small non-toxic construction clay spill Thursday night. Cleanup is underway and the incident poses no risk to public health.


King County is working closely with its construction contractor and the state departments of Ecology and Fish and Wildlife to clean up a small non-toxic clay slurry spill that occurred last night near Lake Sammamish in Bellevue. 

The contractor was using the clay slurry to prepare for the installation of a 1,600-foot pipeline for King County’s Sunset and Heathfield Pump Station and Force Main Upgrade project, which will replace aging and undersized sewer infrastructure. The clay grouts the pipe in place and stabilizes soil around the pipeline opening. 

Some of the spilled material entered the lake near Vasa Park. Though the clay slurry is made of non-toxic bentonite and poses no public health risk, it could be harmful to fish and wildlife in large quantities.

Crews are using vactor trucks to clean up spilled clay on the ground, and King County will consult with Ecology and Fish and Wildlife to address any potential water quality issues. 

The contractor is expected to begin the pipeline installation on Saturday, a day later than previously scheduled. The installation method requires crews to work without stopping and takes an estimated 16 to 24 hours to complete. 

People with questions or concerns can call the project’s 24-hour construction hotline at 206-296-7800.