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Wastewater Treatment

King County, Washington

For questions about the Wastewater Treatment Division website, please send an e-mail message or contact us at:

King Street Center
201 S. Jackson St., Suite 500
Seattle, WA 98104-3855
Phone: 206-477-5371
Fax: 206-684-1741
Telecommunication device for the deaf (TTY): 711

Get Directions to our office location in Seattle, Washington.

Staff Contacts

Planning for growth

System improvements map - click for larger version
Capital projects...
With another million people expected to make their home in the Puget Sound region by the end of the next decade, King County needs to make sure its regional wastewater system keeps pace with growth and meets permitting standards. Here’s an overview of planned projects we’re undertaking through 2030 as part of the Regional Wastewater Services Plan, or RWSP, to protect public health, the environment and the economy for both present and future wastewater customers.

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 another area in which King County and its sewer utility customers work together closely.

Growth management

Under the state's Growth Management Act (Wikipedia, external link), 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 (external link). 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.

Regional Wastewater Services Plan

King County is currently in the midst of the Regional Wastewater Services Plan, or RWSP, adopted in 1999 to ensure the system is meeting growth through 2030. The RWSP includes the many projects listed in the RWSP Annual Report.

Because investments in wastewater infrastructure are significant, the Wastewater Treatment Division's system planning has checks and balances to ensure there is adequate oversight and accountability in carrying out our capital program.

The RWSP requires regular status reports on the projects be delivered to councilmembers. On very large projects, such as Brightwater for example, the King County Council might appoint its own independent monitoring consultant to review project plans, schedules, and associated cost trends during construction. Additionally, the King County Council presides over the budget process and votes to set sewer rates, providing additional oversight on financial matters.

Though clean water is our ultimate goal, the Wastewater Treatment Division also defines success in running an agency that is well-managed, fiscally responsible and compliant with its state and federal pollution control requirements.

Related information

Ratepayer Report 2016
Ratepayer Report