Our stormwater code protects people, property, and the environment by controlling how rainwater runs off of streets, buildings, and parking lots. This stormwater runoff can cause flooding, landslides, and erosion that can damage our homes, businesses, and property. Stormwater is also the main source for pollutants in our creeks, lakes, bays, and other waterways.
Urban areas that collect stormwater runoff in municipal separate storm sewers (MS4s) and discharge it to surface waters must have a permit under the federal Clean Water Act. The Department of Ecology develops and administers National Pollutant Discharge Elimination System (NPDES) municipal stormwater permits in Washington State.
The Department of Ecology is requiring Seattle to update our current codes with additional stormwater control regulations as a condition of our NPDES permit. To meet these requirements, we are revising our existing Stormwater Code (SMC 22.800-22.808) and the associated Stormwater Manual (Directors’ Rule 17-2017). These new rules will replace the current drainage control code and Directors’ Rules which are administered jointly by SDCI and Seattle Public Utilities.
The actual code changes are still to be determined. However, our regulations must be equivalent to Ecology’s NPDES 2019 Stormwater Manual (Ecology Manual). Our updates will consider the following topics:
- Construction site stormwater runoff control/concrete handling
- Technical changes to structural stormwater controls
- Source control
- Clarification of drainage review for Master Use Permit (MUP) and common plans of development
- Combined sewer flow control standard/threshold updates
- Wetland flow control standard
- Stormwater/combined mainline extension requirement clarification
- Addition and clarification of definitions
- On-site Stormwater Management (OSM) list approach
- August 1, 2019: The Department of Ecology reissued the National Pollutant Discharge Elimination System Phase I Municipal permit
- Phase 1 – Equivalency Items to Ecology Manual:
- Public comment period: March through May, 2020 (45 days)
- Draft code and manual submittal to Ecology: July 1, 2020
- Ecology review of draft code and manual: July – November, 2020 (120 days)
- Phase 2 – Non-Equivalency Items (e.g. stormwater/combined sewer mainline extensions, combined sewer flow control standard/threshold, etc.)
- SEPA process
- Public comment period: January 2021
- Phase 3 – Legislative Process and Effective Date
- City Council review and public hearing: Spring 2021
- July 2021: Our updated Stormwater Code and related Director’s Rules are scheduled to take effect
For more information, and to subscribe to our email list, visit our new Stormwater Code Update webpage.