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Construction along South Henderson Street

Pump station improvements

Work at the Henderson Pump Station was completed in Spring 2004. More photos.

The public art on the east wall of the building has been covered to protect it from damage during construction. When work on the pump station is completed in mid-2004, the site will include new trees and landscaping. July 2003

Expansion is mostly occurring under the existing pump station building and includes larger piping, new ties with interconnecting sewer lines, updated controls and a larger generator. July 2003

Pump station construction requires excavation and installation of large connecting storm and wastewater pipelines. Fall 2002

The King County Henderson Pump Station is located on the southwest corner of Seward Park Avenue South and South Henderson Street. It is the site in the Henderson/M.L. King CSO project closest to Lake Washington (refer to project alignment).

The Henderson pump station was last upgraded in 1976. It manages combined waste and storm water flows and controls overflows to Lake Washington. As a result of population growth in the Rainier Beach community over the years, the pump station requires improvements and increased capacity. Currently about 15-30 overflows from the Rainier Beach area occur each year into Lake Washington.

In early 2002, a two-year construction effort got underway to expand the pump station. When completed, the improvements will significantly increase the capacity to direct flows to the storage and treatment tunnel which is now being mined under 42nd Avenue South. Flows can be stored in the new tunnel and, if necessary, treated before being directed to King County treatment plants at West Point and Renton.

Open trench pipeline along South Henderson Street

In 2003 a new pipeline was installed on South Henderson Street. Work began near the Atlantic Boat Launch at Seward Park Avenue South and South Henderson Street, which is a point where overflows of sewers into Lake Washington have occurred in the past.

Crews worked west from Seward Park Avenue South along South Henderson Street to Renton Avenue South, where the open trench met a portal -- or an opening for tunnel construction under M.L. King Jr. Way South. Tunneling continued under ML King Way South to 42nd Avenue South.

Open trench work on Henderson took about seven months. Tunneling under M.L. King Way South was completed in about six weeks.

How trench work impacts were minimized

To reduce disturbances to the community, work crews will excavated the open trench in sections to install new 20-inch- and 42-inch-diameter pipelines. Crews backfilled and restored sections of the street as the work progressed. Detours including lane and street closures were set in place in the immediate area of the work. Flaggers and signs also assisted pedestrians, motorists and businesses as needed.

Return to project alignment map or project illustrations and photos page.

Questions? Contact the project's construction hotline
at 206-684-1251 (TTY 711) or e-mail us.

Henderson / M.L. King CSO Project
King Co. Wastewater Treatment Division
201 South Jackson, Suite 503
Seattle, WA 98104

Updated: July 7, 2004.