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System planning

Planning and building new wastewater infrastructure is extremely complex. It can easily take a decade or more to go from identifying a project need to cutting the ribbon on a newly completed facility.

System planning is an area in which King County and its sewer utility customers work together closely.

Aerial view of Puget Sound near West Point Treatment Plant. The sun is setting across the water.

King County is updating our wastewater plan to improve our system over the next 50 years. An updated plan will help us prepare for upcoming challenges like climate change, aging pipes, and population growth.

Planning efforts will update King County’s Regional Wastewater Services Plan (RWSP), a plan adopted in 1999 that outlines projects to increase wastewater system capacity and function; gives guidance on recovering and recycling beneficial resources from the wastewater treatment process; and provides direction on protecting and monitoring water quality and meeting permit conditions. Learn more about the history of wastewater planning in King County.

Dreaming about what is possible is something we can all do. Join us to create a more sustainable future with the waste we all produce.

How does King County comply with the Growth Management Act?

Under the state's Growth Management Act (Municipal Research and Services Center), local jurisdictions are required to plan essential public facilities such as wastewater treatment to meet their population growth needs. King County is in turn legally required to build wastewater treatment capacity for the jurisdictions and agencies it serves in the central Puget Sound region.

To ensure planning decisions reflect the interest of the regional ratepayers, who ultimately pay for these investments, King County carefully reviews local comprehensive plans and compares growth projections to census data and population forecasts prepared by the Puget Sound Regional Council. The county also looks at its own wastewater flow and monitoring data, and further truth-tests projections by running the data through sophisticated system models to determine where future system capacity might be needed. King County's modeling data has historically proved highly accurate and reliable.

The 34 local sewer agencies that pay King County for safe, environmentally responsible sewage treatment are represented by the Metropolitan Water Pollution Abatement Advisory Committee, or MWPAAC (pronounced "Mew-Pack").

MWPAAC members help ensure we're making cost-effective decisions based on legitimate, emerging needs by working with the county to develop criteria to prioritize and plan projects.

Once project needs are identified, the county develops plans that it shares with MWPAAC's engineering subcommittee and other stakeholders, which might include local elected officials and jurisdiction staff, business leaders, permitting agencies and community members.

The King County Council and County Executive review the comprehensive plans, and only after the council votes its approval do plans for new projects move forward.