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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.


West Point biogas pipe replacement

Sustainable practices

The process to clean wastewater requires lots of energy, but it also produces energy. At the West Point Treatment Plant, renewable energy is produced from the wastewater treatment process and has helped to power the facility since it opened in 1966.

During wastewater treatment, organic solids are pumped into large tanks called digesters that are heated at 98 degrees. In the digesters, bugs (anaerobic bacteria) break down organic material and kill pathogens. This activity creates digester gas, or biogas, that fuels two internal combustion engines much like how gasoline fuels an automobile engine. These engines in the internal combustion cogeneration system power generators that produce electricity for West Point. The exhaust heat from the engines provides heat for boilers, digesters and occupied spaces. The biogas contains about 60 percent methane but also contains sulfuric acid (a byproduct of the hydrogen sulfide in biogas) that wears down on the pipes that carry the renewable energy.

Project description

The purpose of this project is to replace parts of biogas piping connected to the digesters at West Point that have leaks or corrosion. Plans for this project include:

  • Replacing the biogas piping system for the north and south digester pods
  • Replacing piping of various sizes in the treatment plant’s underground tunnel
  • Building a new pipe over the primary sedimentation tanks to provide redundancy for an existing buried pipe. The existing pipe would be rehabilitated with a method known as cured in place pipe
  • Replacing horizontal beams that support biogas piping in the tunnel

The goal of this project is to bring the corroded biogas piping system into a safe and reliable condition through rehabilitating the existing network and extending the life of the overall system.

This project will be implemented in two phases. Construction will take place entirely within the West Point Treatment Plant area. The construction of Phase 1 is underway, with the construction of the whole project expected to be completed by 2025.

What to expect

Construction may require temporary partial shutdowns of digesters for inspection, repair and replacement work. Shutdowns are expected to be less than 24-hours for each occurrence. If shutdowns are planned to last longer, neighbors around the treatment plant and Discovery Park will receive advanced notification regarding any temporary closures or planned gas releases.

Community outreach

We provide ongoing updates here as the project progresses. For more information, contact Dana West at or 206-477-5536 or TTY: 711.

Digesters at West Point Treatment PlantNorth and South Digester Pods

The Power Switchgear Replacement project

Project description

King County Wastewater Treatment Division has a comprehensive maintenance program for our facilities. As part of our system maintenance, we will replace four electrical switchgears at West Point Treatment Plant in 2022 and 2023. Switchgears are a critical part of the wastewater system; they keep wastewater circulating and must operate 24 hours a day. These switchgears are about 45 years old, nearing the end of their useful life, and need to be replaced. This will ensure that the system operates reliably for decades to come.

Project schedule

The project plans to complete the pre-design phase by the end of 2020. King County will then conduct the design phase between January and August 2021 (estimated), with construction estimated to take place during the 2022 - 2023 dry seasons. The switchgear replacement is planned for completion in 2023. 

The Design phase: Starting in approximately January 2021, King County will design replacements for four electrical switchgear lineups in the intermediate pump station and effluent pump station process areas at the plant. 

Community outreach

We provide ongoing updates here as the project progresses. For more information, contact Dana West at or 206-477-5536 or TTY: 711.

West Point Treatment Plant seismic upgrade

August 2020 - What's happening now?

The project is currently in the final stages of design, with final design expected to be complete in September. In this phase the team refines the project design, conducts environmental review, and acquires permits and property rights. Following the completion of design, the project team will begin preparing for construction, expected to begin in February 2021.We will continue to provide updates as the design is finalized, and to prepare the community for construction in 2021.

Over the past year, we have:

  • Developed designs for the removal of the existing roof structure and other upgrades needed to meet required seismic safety for the sedimentation basins.
  • Begun planning for increased truck traffic in Discovery Park and other local streets by: performing a study to ensure that construction trucks don’t cause road blockage or closures, placing limits on trucks’ weight to reduce damage to roadways, and placing restrictions on construction truck and equipment noise levels and hours of operation.
  • Obtained required permits from the City of Seattle, and state and federal agencies

We will continue to keep the community up to date, answer questions, hear your input, and address concerns. The team is committed to continuing outreach during the design phase and into construction. We will be reaching out to the community to find the best way to keep in touch with you!

Project description

Covered sedimentation tanks at West Point

West Point Treatment Plant is undergoing upgrades to make the facility more resilient in the event of an earthquake. We are improving large enclosed sedimentation tanks that play a key role in the wastewater treatment process. A seismic evaluation performed in 2010 showed that the roof above the tanks did not meet minimum seismic safety standards.

In order to improve resilience of the facility, this project will include:

  • Removing a series of large, concrete beams above the tanks
  • Improving the odor control system
  • Increasing the wall thickness between the two tanks
  • Upgrading the walkways on the tank walls so staff can access the facility safely and efficiently

These tanks not only clean wastewater in order to protect public health but also allow King County to recycle valuable resources for the Puget Sound region. The sedimentation tanks are where about 60 percent of organic solids in the flows from our homes, schools and businesses are removed. Wastewater sits in sedimentation tanks for about six hours so that heavy materials sink and light materials float. These organic materials are then skimmed from the top and scraped off the bottoms of the tanks and further treated, recycled and used in products such as Loop, a nutrient-rich biosolids product sold to farms and forests as an alternative to chemical fertilizers.

Located in Discovery Park, West Point cleans wastewater from homes, schools and businesses in a large area that includes Seattle, Shoreline, north Lake Washington, north King County and south Snohomish County.

West Point Treatment Plant
Upgrades for this project will focus on two twin sedimentation tanks (labeled above as West primary treatment and East primary treatment), where more than half of organic solid waste is clean out in the wastewater treatment process.

Project schedule

The project is currently in the design phase and expects to complete final design in late 2020. Construction is expected to begin in early 2021 and take approximately two years.

What to expect

During the project, there will be increased vehicle traffic through Discovery Park to West Point Treatment Plant, mainly due to the removal and hauling out of large concrete beams that are part of the existing roof structure over the sediment tanks. Community members may notice construction-related traffic and noise, but work activities will otherwise be inside the boundaries of the treatment plant. More information will be provided as the project design is finalized.

Project history

In 2017, King County began an alternatives analysis process to identify the best way to upgrade the sedimentation tanks to meet seismic standards. Several alternatives were studied and considered, including options to upgrade the existing framing or removing the roof altogether. Following alternatives analysis, the County determined the best approach was to remove the roof. Removing the roof reduced both the overall project cost and upgrades required for the facility. The sedimentation tanks have been operating continuously since 1966. The project will also include an upgrade of the existing odor control system, which was installed in the late 1990s.

Community outreach

King County recognizes that Discovery Park is a popular spot for the local community as well as residents city-wide. We will provide ongoing updates on our website as the project progresses. For more information, contact Dana West at or 206-477-5536.

Water Reservoir Modifications Project

May 2020 Update

Construction completed: King County crews completed construction on the Discovery Park reservoir modification project in the spring of 2020 and restored the area around the new outfall pipe and diffuser by replanting native prairie plant and shrub species. Within the restoration area, King County will be controlling weeds and watering native plantings. King County is coordinating with Seattle Parks and Recreation to complete the replanting of trees beginning in the fall 2020 planting window.

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 Dana West at

Meetings, news, project materials

Contact us

For more information about capital projects at West Point Treatment Plant, please contact Dana West, Community Services,, 206-477-5536.

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

1400 Discovery Park Blvd.
Seattle, WA 98199

Directions and map

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Did you know?

WPaerial_1974-v-1999From 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.