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Treatment Planning Program

We have some of the largest wastewater treatment plants in the country. It takes a decade or more to build large wastewater projects, so it’s important we plan ahead.

As our region's population continues to grow and wastewater treatment regulations evolve, the Treatment Planning Program is working to determine the changes and upgrades that will be needed at each of our five wastewater treatment plants:

The program carefully evaluates current and forecasted capacity needs and regulatory requirements, helping King County make the right decisions and investments, at the right time, for the most effective treatment of the region’s wastewater. We plan for improvements at the individual treatment plants and throughout the system as a whole.

As the wastewater needs of the region grow and change, the Treatment Planning Program helps align, plan, and ultimately deliver any system updates to prepare for the future. We work to identify and plan for policies, conceptual capital projects, and funding needed to clean water and protect public health and the environment for decades to come.

What we are working on

Capacity Planning: Following the Treatment Plant Flows and Loadings Study, WTD has capacity constraints to address at each regional treatment plant.

Regulatory Planning: With new regulations for nitrogen removal, WTD needs to plan how to meet changing permit requirements.

Library and resources

Below are reports, studies, and other technical resources related to the Treatment Planning Program.

South Plant Solids Thickening Technology Evaluation

South Plant Solids Thickening Technology Evaluation, June 2022. This technical memorandum summarizes a review and evaluation of available solids thickening technologies for King County’s South Treatment Plant.

Treatment Plant Flows and Loadings Study

Treatment Plant Flows and Loadings Study, November 2019. This Report summarizes the capacity limitations and timing of those limitations for the three regional treatment plants.

Wastewater Flow and Loadings Forecasting

Wastewater Flow and Loadings Forecasting. These reports document the methodology and results of peak flow and wasteload projections for King County’s treatment plants (West Point, South Plant, Brightwater). 

Nitrogen Removal Study

Nitrogen Removal Study, September 2020. This report summarizes the background, approach, and results of the King County Wastewater Treatment Division’s (WTD) Nitrogen Removal Study.

Half-Century Assessment of the West Point Treatment Plant

Half-Century Assessment of the West Point Treatment Plant, December 2017. The report assesses changes in the operating context over West Point’s 50 year history, current and projected capacity constraints, and potential system vulnerabilities, and how well positioned the plant is to meet these challenges in the future.