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Natural Resources and Parks
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Pump station overflows in West Seattle during heavy rainfall, high tide


King County crews quickly responded Jan. 18 to a wastewater treatment facility in West Seattle that flooded with stormwater and wastewater during heavy rainfall and high tides.


During a period of heavy rain and high tides, King County crews quickly responded when the Alki combined sewer overflow (CSO) treatment facility flooded with mixed stormwater and wastewater on Wednesday, Jan. 18.

During the storm, the County’s 63rd Avenue Pump Station sent high flows to the Alki CSO facility at 3380 Beach Dr. SW.

The pump station is designed to discharge treated stormwater and wastewater flows exceeding capacity through an outfall extending into Puget Sound. High tides can add to the flow going to the CSO treatment facility.

High flows from the pump station flooded the Alki CSO treatment facility, causing an overflow into a nearby storm drain that empties into Puget Sound. The volume and duration of the overflow have not yet been determined.

King County reported the overflow to health and regulatory agencies. A cleanup crew and vacuum truck removed remaining wastewater from the building. King County employees posted signs by the beach and employees with the County’s Environmental Lab conducted water quality monitoring.

Operations employees are investigating the equipment problem.

Information about King County’s CSO treatment facilities is available online at

This release is also posted on the Department of Natural Resources and Parks website,