Stormwater management code and plan updates
Stormwater management code and plan updates
Review, comment and give feedback on the regulatory documents King County uses to guide stormwater management and pollution prevention
Stormwater is regulated and managed through King County code Title 9, the Surface Water Design Manual, the Stormwater Pollution Prevention Manual, and annual reports: Stormwater Management Plan and Stormwater Action Plan.
Those documents are open to the public for review, suggestions or comments and offer background on stormwater design and regulations.
Stormwater is one of the infrastructure needs that is not obvious until rainfall causes powerful stream flows and erosion, flooding, or water pollution. These challenges come from development, when buildings and paving alter natural areas that had allowed rain to be slowed, captured and cleaned.
Open for review and comment:
King County Code Title 9
King County Code Title 9 regulates surface water and stormwater management. Title 9 helps preserve valuable resources like water quality, habitats, and open space. It also provides requirements for designing stormwater management in King County. These regulations supplement our technical Surface Water Design Manual.
We are updating Title 9 to meet regulatory requirements that reduce impacts from development. The revisions will align with our Surface Water Design Manual update. These updates are to clarify and streamline drainage regulations.
Updates include:
- Have consistent terms and clear definitions
- Meet regulatory requirements
- Improve code administration
- Foster equitable program management
- Protect water quality and fish and wildlife habitat
There will be several opportunities for community input throughout the process. We welcome your questions, concerns, and comments by email at any time to Leah Mikulsky at lmikulsky@kingcounty.gov.
Surface Water Design Manual and Stormwater Pollution Prevention Manual
King County is proposing to update the 2021 (Amended 2024) Surface Water Design Manual and the 2021 Stormwater Pollution Prevention Manual to comply with the Washington State Department of Ecology Phase I Municipal Stormwater Permit (the Permit). A 45-day comment period is from May 1, 2026, through June 15, 2026.
Surface Water Design Manual updates includes edits required for compliance with the Permit and changes to improve environmental protection, such as:
- Increasing minimum requirements for redevelopment project thresholds;
- Clarifying project exemptions; and
- Updating runoff treatment performance goal thresholds.
Stormwater Pollution Prevention Manual updates for businesses presents best management practices (BMPs) for pollution prevention. These are practices businesses use to prevent pollution and help prevent clean up liability and can highlight other cost savings.
Drafts of the proposed public rules, redlined versions of the Surface Water Design Manual and the Stormwater Pollution Prevention Manual, and proposed changes are at:
- 2026 Stormwater Design Manual and Public Rule: DNRP public file sharing site - 2026 SWDM and Public Rule - All Documents
- Stormwater Pollution Prevention Manual: DNRP public file sharing site - Documents - 2026 SPPM and Public Rule - All Documents
Request copies of the proposed rules and send comments to:
For the Surface Water Design Manual: Mark Wilgus, Water and Land Resources Division, 201 S. Jackson St., KSC-NR-6300, Seattle, WA 98104; mark.wilgus@kingcounty.gov or call 206-477-4848.
For the Stormwater Pollution Prevention Manual (Please include the rule number in your comments): Robert Bernhard, Water and Land Resources Division, 201 S. Jackson St., KSC-NR-6300, Seattle, WA 98104; rbernhard@kingcounty.gov or call 206-263-8979.
Questions? Contact Mark Wilgus at 206-477-4848 or mark.wilgus@kingcounty.gov.
Stormwater Management Plan (SWMP) and Stormwater Action Plan (SMAP)
King County is a permittee under the Phase I Municipal Stormwater Permit – part of the Clean Water Act’s National Pollutant Discharge Elimination System (NPDES) Permit Program to protect our waters. As a requirement of the permit, King County updates the Stormwater Management Program Plan yearly, as well as submitting an Annual Report to the Washington State Department of Ecology.
These plans are open year-round for comment. Find the latest plans at King County Stormwater Management Program Annual Report - King County, Washington and send your comments to stormwater@kingcounty.gov.
King County Code Title 9
Comments welcome on changes that include:
- Updated terms and clear definitions
- Meeting regulatory requirements
- Improving code administration
- Equitable program management
- Actions to protect water quality and fish and wildlife habitat
We welcome your questions, concerns, and comments to Leah Mikulsky at lmikulsky@kingcounty.gov.
Surface Water Design Manual and Stormwater Pollution Prevention Manual
Send comments to:
For the Surface Water Design Manual: mark.wilgus@kingcounty.gov; Mark Wilgus, Water and Land Resources Division, 201 S. Jackson St., KSC-NR-6300, Seattle, WA 98104; or call 206-477-4848.
For the Stormwater Pollution Prevention Manual (Please include the rule number in your comments): rbernhard@kingcounty.gov; Robert Bernhard, Water and Land Resources Division, 201 S. Jackson St., KSC-NR-6300, Seattle, WA 98104; or call 206-263-8979.
Questions? Or to request copies of the proposed rules, contact Mark Wilgus at 206-477-4848 or mark.wilgus@kingcounty.gov.
Stormwater Management Plan (SWMP) and Stormwater Action Plan (SMAP)
The Stormwater Management Program Plan (SWMP) describes work completed in the previous year, and the Stormwater Action Management Plan (SMAP) describes activities planned for the coming year and are open year-round for comment. Find the latest plans at King County Stormwater Management Program Annual Report - King County, Washington and send comments to stormwater@kingcounty.gov.