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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 Treatment Plant power quality improvement

Visit project page HERE.

West Point Treatment Plant Raw sewage pump replacement

raw sewage pumps at West Point Treatment Plant

Project description

The purpose of this project is to replace the Raw Sewage Pump system at King County’s West Point Treatment Plant. The system was constructed in 1966 as a key part of the original treatment plant, with its four huge pumps in continuous service since that time. Pumping hundreds of millions of gallons of untreated sewage for more than 50 years has resulted in significant wear on the pumps and associated piping. Continual preventive maintenance and repair of the aging pumps and engines have increased with the age of the system, resulting in significant annual costs to maintain the reliability of the aging equipment.

The project will increase the reliability and capacity of the pump system.

Project phase and schedule

The project is currently in the preliminary design phase, when the team evaluates and analyzes potential project alternatives. Based on analysis, the team will select a preferred alternative and design sufficiently to establish a project baseline. The County may initiate activities requiring long lead times, such as permitting, during this phase.

The team expects the project to move into the final design phase in late 2021. Construction is expected to begin as soon as 2024.

Community impacts and outreach

The County anticipates that impacts to the nearby community during construction, such as noise, will be minimal as construction will take place inside the treatment plant walls and the design uses existing site footprints.

We will provide ongoing updates on our website as the project progresses. For more information, contact Dana West at or 206-477-5536 or TTY: 711. Sign up for email or text updates for current West Point Treatment Plant capital improvement projects below.

West Point Treatment Plant 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 was completed October 2020, with a Phase 2 construction expected to start in spring. The construction of the whole project is expected to be completed by 2027.

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 West Point Treatment Plant power monitoring upgrades

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 sedimentation tanks seismic upgrade

Visit project page HERE.

Water Reservoir Modifications Project

April 2021 Update

two workers planting a treeContractors unload trees to plant at Discovery Park last year.

King County restoration contractors completed planting 23 Garry Oak and 29 Douglas Fir trees at various locations in Discovery Park last year and now those young trees are taking root. See photos and read more about how we restore natural areas after construction in our Clean Water Stories blog post.

The tree plantings are the final part of an overall restoration plan that began in spring of 2020 with native prairie and shrub species plantings completed in the area around the new outfall pipe and diffuser. Within the restoration area, King County will be controlling weeds and watering native plantings. Impacted parts of trails have also been restored.

Protecting people and water sources

The King County Wastewater Treatment Division upgraded 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 protected public health in several ways. King County upgraded the underground water facility to provide safe and efficient access for annual inspection, and to 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 installed new above grade air gaps over each water tank.

The contractor installed 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 built this project

This work took several 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 used the existing access for the site. 

Construction involved 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 was installed in an excavated trench, which was then backfilled and replanted.

This project affected some vegetation. The project team 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.

In spring of 2020, King County began restoration of natural areas impacted by construction by planting native prairie and shrub species in the area around the new outfall pipe and diffuser. In late 2020, the County’s restoration contractors completed planting 23 Garry Oak and 29 Douglas Fir trees at various locations in Discovery Park. The tree plantings were the final part of the overall restoration plan. Within the restoration area, the County will be controlling weeds and watering native plantings. Impacted parts of trails have also been restored

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

If you’d like to receive email or text updates on the West Point Treatment Plant current projects:

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.