King County Vashon Wastewater Treatment Plant

We invite your comments on the development of the King County Vashon Wastewater Treatment Plant draft permit no. WA0022527.

The proposed draft permit includes new conditions necessary to regulate the discharge of nutrients from the Vashon Wastewater Treatment Plant to Puget Sound.

You may view the draft permit, draft fact sheet, and other permit documents at King County Vashon Wastewater Treatment Plant or visit the Water Quality Permitting and Reporting Information System (PARIS) webpage.

To comment or request a public hearing, use one of the ways listed below.

We will schedule a public hearing on the proposed permit changes if we determine that there is significant public interest. To request a public hearing, please contact nwrowqpermits@ecy.wa.gov by August 28, 2026, and include the permit number and your reason for requesting the hearing.

Background

We regulate wastewater released from municipalities and industries using the National Pollutant Discharge Elimination System (NPDES) Wastewater Discharge Permit. This permit regulates wastewater that goes directly into Puget Sound. All wastewater must be treated and meet the applicable water quality standards before it goes into surface water to protect human health and aquatic life. Learn more about water quality individual permits.

Discharges of excess nutrients — particularly nitrogen — to Puget Sound from domestic wastewater treatment facilities are contributing to low oxygen levels. The proposed requirements are intended to maximize what the existing treatment facilities can reasonably do to reduce nutrients, with their existing technology. Facilities will also begin planning for upgrades needed to improve nutrient removal in the future. The updates are focused on four concepts:

• Monitoring the current nitrogen levels in the facilities’ discharge water
• Evaluating annual nitrogen loads and requiring corrective actions if they are too high
• Incorporating nutrient reduction into regular operations and maintenance
• Assessing nutrient reduction technologies in two ways:
  • Identifying what treatment changes the community can reasonably afford (called the AKART analysis; AKART stands for all known, available and reasonable methods of prevention, control and treatment). This analysis focuses on identifying the best level of treatment the community can afford to build and operate.
  • What it would take to change the existing treatment systems to achieve a specified low-level nitrogen target (called the Nutrient Reduction Evaluation).