Water Treatment Plant General Permit

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Permit documents

• Current Permit (effective Sept.1, 2024)
  • Fact Sheet
  • Appendix E: Response to Comments

Water treatment plant reports 

Between 2014 and 2018, we reviewed data concerning water treatment plants in Washington, including:

• Arsenic monitoring data provided by permittees.
• Data about raw water sources, finished water production rates, volumes of wastewater discharged, and populations served for more than 900 water treatment plants statewide.

The two reports identified below summarize that work and our findings and conclusions.

• Assessment of Arsenic Monitoring Results Report
• Preliminary Re-Evaluation of Discharges Report

Does my facility need this permit?

You need this general permit if your water treatment plant discharges wastewater to surface waters and:

• Produces 35,000 gallons per day or more (monthly total divided by the number of days in the month) of finished drinking and industrial water.
• The primary function of the facility is treatment and distribution of potable or industrial water.
• Produces wastewater by filtration processes.
• Is not a part of a larger permitted facility.

Operations not covered by this permit include discharge of wastewater that is:

1. Produced by one of the following processes:
   • Ion exchange
   • Reverse osmosis
   • Slow sand filtration
2. Sent to a publicly-owned treatment works delegated by Ecology.
3. Released to land where runoff or overflow is impossible.

If any of these are the case, you may need an individual permit.

Permit application, forms, and resources

Contacts for more information