Henderson/M.L. King CSO Project -- King County Wastewater Treatment Division

How the new CSO project helps protect Lake Washington and Rainier Beach

Exterior of Henderson Pump Station
Today, the original 1970s brick sculpture on the west side of the Henderson Pump Station, “Quest for Clean Water” by well-known local artist Richard S. Beyer, is more visible for public view and framed by added architectural details and landscaping.

New pumps at the Henderson Pump Station Three new pumps have been installed in the main pump room on the lower level of the Henderson Pump Station. Each unit can pump more than 4 million gallons per day. Two submersible pumps are in an adjacent underground “wet pit,” each with the capacity to pump about 6 million gallons per day.

The inlet regulator diverts wet-weather flows into the combined sewer tunnel for treatment and temporary storage. During dry weather, flows are directed to the Henderson trunk sewer along Martin Luther King Jr. Way South. Odor control units use activated charcoal.

Pumping storm flows away from Lake Washington

The Henderson Pump Station–located across from Lake Washington, the Atlantic City Boat Ramp and Beer Sheva Park at Seward Park Avenue South and South Henderson Street–is the project’s most visible facility. The former Municipality of Metropolitan Seattle (Metro) built it in the mid-1970s with a capacity to pump 7.5 million gallons per day of combined sewage. It replaced an older, smaller City of Seattle pump station that sat across the street next to Rainier Beach High School.

Today, the newly expanded Henderson Pump Station has nearly tripled in capacity while maintaining the same footprint. It can carry more than 20 million gallons of stormwater and wastewater a day away from the lake during and after heavy rainfalls.

Most of the pump station’s expansion is not obvious from the street because it’s taken place underground. With five variable speed pumps, this state-of-the-art facility can now collect peak wet-weather flows, which previously overflowed to Lake Washington. From the pump station, flows are pumped west below Henderson Street through new 42- to 72-inch pipelines to a new combined sewer storage tunnel.

Regulating incoming flows to the combined sewer storage tunnel

The beginning of the storage tunnel is at 42nd Avenue South between Fairbanks Avenue South and Carkeek Drive South. Flows entering the tunnel pass through an inlet regulator, a multilevel underground facility that diverts wet weather flows into the combined sewer storage and treatment tunnel.

The inlet regulator is a fairly small, one-story building above ground in a parklike setting. But the facility reaches 80 feet underground in five levels to house advanced electrical controls, an emergency generator, flow control gates, odor control equipment and a hypochlorite disinfection system.

More photos and description of the completed project:

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