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Capital improvement projects at West Point Treatment Plant focus on protecting ratepayer investments through improving system reliability, protecting worker and public safety and the environment, and increasing efficiency.

Water Reservoir Modifications Project - 2019

Informational Open House: King County held an Informational Open House on Saturday, Feb. 23, 2019, at the Discovery Park Environmental Learning Center. View news release, frequently asked questions , presentation boards , and meeting summary . For more information on this project, contact Eunice Lee at

Protecting people and water sources

King County Wastewater Treatment Division (WTD) will carry out a project to upgrade the existing underground water facility that serves West Point Treatment Plant, South Beach, and the West Point Lighthouse. The water system carries both potable (drinkable) and non-potable water. Potable water is used at the treatment plant, in water fountains, and at the lighthouse.  Non-potable water is used at the treatment plant for industrial processes. The potable water is separated from the non-potable water by a below-grade air gap in the potable water tank.

Project description

This project will protect public health in several ways. King County will upgrade the underground water facility to provide safe and efficient access for annual inspection, and meet current standards for protecting water sources.

The existing below-grade air gap keeps the water sources separate in the event of an overflow inside the underground structure. Overflows are very rare, but could cause mixing of the two water sources and damage to equipment. King County’s contractors will install new above grade air gaps over each water tank.

The contractor will install an approximately 460-foot outfall pipe to address the potential for overflows. In the very rare event of an overflow, the pipe will carry flows away from the facility to a discharge site, protecting water sources and the facility.

How we will build this project

This work is expected to take about three to five months. The work area is located near the Loop Trail, just north of where the path forks and splits off at South Beach Trail. Equipment and vehicles will use the existing access for the site. 

Construction will involve demolition of the concrete access hatches to the reservoirs, installing new interior pipes, and building a new roof and access hatch to protect the entryway from rain and debris. The outfall pipe will be installed in an excavated trench, which is then backfilled and replanted.

This project will affect some vegetation. The project team has coordinated with the City of Seattle Parks Department on a plan to restore plants with a palette that blends in to the natural environment and supports the park’s wildlife.

The South Beach area that park visitors cherish today did not look like this long ago. The West Point Treatment Plant once took up far more space. When West Point Treatment Plant was upgraded in the 1990’s, designers used improved treatment technologies to make the plant footprint smaller.  This opened up space for people and wildlife on trails and natural areas around the treatment plant. King County’s employees still maintain many of these features today. 

Location of the work area in relation to West Point Treatment Plant 

Work area

Wildlife considerations 

During design, WTD determined that an avian nesting study will need to be conducted. Construction will take into consideration potential impacts on wildlife, including the nesting periods of birds, and comply with the federal Migratory Bird Treaty Act. The project will include some cutting of small branches on deciduous trees and some brush, including black berry bushes. 

Community outreach

King County recognizes that Discovery Park is a popular spot for bird enthusiasts and anticipate that this project will generate interest from community members who frequent the park. WTD will provide ongoing updates as the project progresses. For more information, contact Eunice Lee at

Contact us

For more information about capital projects at West Point Treatment Plant, please contact Eunice Lee, Community Services,, 206-263-1614.

24-hour emergency and odor reporting:   206-263-3801
Administration:  206-477-9800

1400 Discovery Park Blvd.
Seattle, WA 98199

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From then to now: Since 1974, when open sludge lagoons were present on the South Beach at Discovery Park, West Point Treatment Plant has been upgraded to provide award winning wastewater treatment service to our growing region, protecting Puget Sound water quality. Covering treatment processes, installing odor scrubbing equipment, and modifying maintenance practices helps to control odor. Landscaping improvements have restored shoreline areas to a natural area with public access.