North Beach CSO Control Project

April 2013 Update – Outfall survey and repair work begins week of April 22
King County is continuing maintenance and repair work on the North Beach Pump Station outfall. On April 22 and 26, the County’s contractors will conduct marine and land surveys of the outfall alignment. In late April-May, a diving contractor will repair holes in the outfall pipeline (PDF). More information about work to assess and maintain the outfall can be found here.

Project vicinity


North Beach Pump Station, located on King County property next to Blue Ridge Park, is built on the footprint of the former City of Seattle treatment plant.

Project description

King County is designing and building an underground storage tank in the right-of-way in N.W. Blue Ridge Drive and Triton Drive N.W. This facility will need to store about 230,000 gallons of peak flows when the North Beach Pump Station reaches maximum capacity.

Learn more about the project area and elements.

Why does King County need to do this project?

In 2008, King County reported that the North Beach combined sewer overflow facility has 10 overflows per year on average that discharge a total of 2.2 million gallons into Puget Sound off North Beach. At North Beach, King County is working to meet current regulations set by the Washington Department of Ecology require no more than one untreated discharge per year on a long term average.

Project schedule

View meeting calendar for upcoming public meetings, and North Beach CSO Control Project Timeline (PDF).

Regional facilities at North Beach

The North Beach Pump Station has provided wastewater service for the area since 1962 by collecting flows from the City of Seattle’s local sewer system. These flows are conveyed to the Carkeek Wet Weather Facility where they are either pumped to the county’s West Point Treatment Plant or, in large storm events, treated on site. The North Beach Pump Station is built on the footprint of what was once a City of Seattle treatment plant. The walls and foundation are from the original treatment plant.

Did you know?

• The North Beach Pump Station is built on the footprint of what was once a City of Seattle treatment plant. The walls and foundation are from the original treatment plant.
• When Metro was created by voters in 1958 to provide regional wastewater conveyance and treatment, local treatment facilities like the one in North Beach were considered for conversion to pump stations to bring flows to regional treatment facilities.
• The current service area for the North Beach Pump Station is 633 acres. Wastewater from additional areas within Blue Ridge are conveyed by gravity to the North Beach force main, where they combine with pumped flows to the Carkeek Wet Weather Facility.
• The North Beach Pump Station is largely built underground with access hatches and ventilation equipment above ground. Four pumps are used to convey up to 3 million gallons per day (mgd) of wastewater to Carkeek.
• The CSO facilities include a deepwater outfall upgraded in the 1970’s from the outfall that served the original treatment facility. Discharge to a second outfall, which usually conveys stormwater, helps to prevent backups into homes in large storms.
• The new CSO facility will introduce odor control at the North Beach site. Currently there is no odor control associated with the North Beach Pump Station. King County has not received odor complaints about this facility.