Public comment period

March 25 - May 8

King County is amending its Surface Water Design Manual to include a soil mix option that is proving to be successful in removing the chemical called 6PPD-Q which could reduce fish mortality. The amendment offers an  opportunity for public review and comment.

Drafts of the proposed public rules are available below:

How to comment

Comments can be submitted by phone, email, postal service, at an online public comment meeting (date to be determined), or using the comment form below.

Email: Mark Wilgus

Voicemail: 206-477-4848

U.S. Postal Service:
ATTN: Mark Wilgus
Water and Land Resources Division
201 S. Jackson St, Suite 5600
Seattle, WA 98104

Online public comment meeting: Date to be determined.


Question title

Online comment form.

Closed for Comments

About this revision

Surface water or stormwater is rainwater that picks up pollutants from building and land surfaces. With stormwater treatment that mimics nature, we can remove pollutants from stormwater.

Adding bioretention using the new soil mixes to the SWDM adds to our list of tools to help reduce pollutants such as sediment, heavy metals like copper and zinc, and phosphorus – a nutrient that promotes excess algae growth. 

The chemical 6PPD-Q is released from tire particles into stormwater. The University of Washington and Washington State University researchers have identified it as the chemical that is killing Coho salmon. 

More information can be found on the Surface Water Design Manual web page.


Frequently Asked Questions

2021 Surface Water Design Manual

This is a technical manual detailing stormwater management requirements for parcel development in King County, WA and those municipalities that have adopted this manual. At present the most current version is the 2021 Surface Water Design Manual (SWDM). A complete update will take place in 2025.

6PPDQ is a chemical used to preserve tires that has been linked to coho salmon mortality. Stormwater washes the "tire dust" containing 6PPDQ off roads into salmon bearing streams across Puget Sound. Read more.

Early data from a King County study showing the effectiveness of the new High Performaning Bioretention Soil Mix in reducing coho mortality has prompted this revision to recommend its use in stormwater design. Read more.