The Thornton Creek sewer is an approximately 1.2-mile-long sewer pipe that collects wastewater from other pipes in our sewer system, serving 9.6 square miles of North Seattle and Shoreline. The pipe carries this wastewater to the Matthews Park Pump Station, where it is then conveyed and treated at the West Point Treatment Plant.
During heavy storms, the sewer pipe sometimes reaches its capacity. To avoid possible overflow, King County will need to either reduce the amount of stormwater and groundwater entering the system – known as infiltration and inflow (I/I) – or increase the size of the sewer pipe. Increasing the size of the sewer pipe may also require more costly upgrades to other parts of the regional wastewater system, including Matthews Park Pump Station.
Phase one of the Thornton Creek Basin Sewer Study and Upgrade Project is complete.
Previous project updates
- Study conclusion mailer, March 2023
- Sewer Pipe Smoke Testing in Your Neighborhood, June 16, 2022
- Frequently Asked Questions, June 2022
- Fact Sheet, Winter 2022
- Thank you for taking our survey, November 2021
- Sewer inspections coming soon to your community, September 2021
- Thornton Creek Basin Sewer Survey, September 2021