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King County Wastewater Treatment Division readies for wet weather


Natural Resources and Parks
Public Affairs

King County Wastewater Treatment Division readies for wet weather


Wet weather season arrived in Puget Sound in a big way Sept. 23, with much of the region receiving an inch of rain and pushing hundreds of millions of gallons of rainwater through the King County Wastewater Treatment Division (WTD) system. With more rain in the forecast, WTD remains on the job 24/7 to ensure the region’s wastewater treatment service is well-prepared for an emergency or inclement weather.


Ensuring wet weather season readiness, the King County Wastewater Treatment Division has inspected and replaced equipment, updated control systems and increased training of plant operators in a continual effort to make sewer operations more resilient during storms.


Operation crews have conducted annual wet weather refresher training, mechanical and electrical teams have inspected the pumps at offsite stations, and the instrumentation/electrical teams have fine-tuned alarm systems. Personnel have been placed on standby and are ready to respond around the clock. COVID-19 health and safety protocols are rigorously practiced at the plants, and flu vaccinations have been made available onsite to all.

All 47 pump stations throughout the wastewater service area have been inspected and power generators have been tested, fueled and are ready to provide power in case of an outage. Force main repairs and reinforcements were made at two pump stations and obsolete pump controls were upgraded and replaced to prevent overflows.

Throughout the year, WTD staff trains and hones their on-call readiness for wet weather that can sometimes stress the wastewater system. Within Seattle city-limits, the system is a combined one, where stormwater drains carry water to the West Point Treatment Plant to be processed with wastewater from households and businesses. When it rains, about 80% of the flow through the plant is stormwater.

West Point Treatment Plant has made significant upgrades, including increased plant safety system testing, additional staffing, updating protocols and regular training on how to respond in emergency situations. Older equipment has been replaced to increase reliability of operations during high flows. Hydraulic power systems have been installed to improve reliability and resiliency of backup operations. WTD installed a system that keeps short power sags from affecting pump operation and has a new system to automatically switch power sources.

WTD has made tremendous investments in wet weather infrastructure in recent years, and will invest over $134 million in asset management for 2019-2020.

The Rainier Valley Wet Weather Storage Facility, completed in 2018, included construction of a combined sewer overflow (CSO) underground tank and sewer pipelines. Located in Seattle’s North Beacon Hill and Columbia City neighborhoods, it controls the overflow of stormwater and sewage into the Duwamish River during heavy rains.

The Georgetown Wet Weather Treatment Station is currently under construction and should be completed by 2022. When constructed, the station will treat up to 70 million gallons of combined rain and wastewater a day that would otherwise have discharged directly to the Duwamish River without treatment during storm events.           









Marie Fiore, 206-247-9260

About the King County Wastewater Treatment Division

King County’s Wastewater Treatment Division protects public health and enhances the environment by collecting and treating wastewater while recycling valuable resources for the Puget Sound region. The division provides wastewater treatment services to 17 cities, 17 local sewer districts and more than 1.8 million residents across a 420-square-mile area in King, Snohomish and Pierce counties.