Draft Stormwater Regulations Ready for Public Review

Our stormwater code protects people, property and the environment by controlling how rain water runs off of streets, buildings, and parking lots. 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 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. Our regulations must be equivalent to Ecology’s NPDES 2012 Stormwater Manual. To meet these requirements, we are revising our existing Stormwater Code (SMC 22.800-22.808) and the associated Directors’ Rules. These new rules will replace our current Stormwater Code and Directors’ Rules that are administered jointly by DPD and Seattle Public Utilities.

We are holding a public meeting on June 3 to discuss our revised stormwater regulations and to get your feedback.

Tuesday, June 3, 2014
4:00 – 6:00 p.m.

Seattle Municipal Tower
Room 4050
700 5th Ave.

To review the initial draft stormwater regulations and/or participate in a survey, please visit our Stormwater Code & Rules Update website. This is an initial and informal review period. After receiving equivalency from Ecology, the final drafts will be available for formal public review and comments. We anticipate this to take place in winter 2015.

You can also submit comments and join the Stormwater Code listserv by sending an email to stormwatercode@seattle.gov. Comments will be accepted through July 2014.

Our proposed changes to Seattle’s Stormwater Code include:

  • Transition to Revised Stormwater Code – we added permit expiration and effective dates, including building and master use permits, as a new code section 22.800.100.
  • Implementation of On-site Stormwater Management – the Green Stormwater Infrastructure to the Maximum Extent Feasible (GSI to MEF) calculator/menu approach is replaced with an applicant’s choice of one of the following:
    • A prescriptive On-site List of GSI Best Management Practices (BMPs)
    • An On-site Performance Standard
  • Threshold Changes to Single-family Residential Projects (SFR) – SFR projects no longer have a 1,500 square foot impervious surface credit and the threshold for SFR projects to meet the On-site Stormwater Management requirement (formerly GSI to MEF) is increased to 2,000 square feet of impervious surface to match Ecology’s threshold.
  • Roadway Project Threshold Changes for Water Quality Treatment – The water quality treatment threshold for Roadway Projects now reflects the Stormwater Management Manual for Western Washington.

Our proposed changes to Seattle’s Stormwater Manual include:

  • Stand-alone document – The previous Seattle Stormwater Manual (2009) consisted of four separate Directors’ Rules. Three additional Directors’ Rules interpreted sections of the Stormwater Code that were not interpreted by the 2009 Stormwater Manual. Our goal for this update is to create one stand-alone manual that is equivalent to the Department of Ecology’s Stormwater Management Manual for Western Washington (2012). Our new stormwater manual will provide users a one-stop shop for all necessary regulatory information, along with design and maintenance standards and information tailored to Seattle conditions.
  • Formatting – The 2015 Stormwater Manual includes five volumes:
    • Volume 1 – Project Minimum Requirements
    • Volume 2 – Construction Control
    • Volume 3 – Project Stormwater Control
    • Volume 4 – Source Control
    • Volume 5 – Stormwater Code Enforcement
  • Content intent – Our goal is to have a straightforward, concise regulatory manual that is equivalent to Ecology’s Stormwater Management Manual for Western Washington.
  • New Minimum Requirements Volume – We created Volume 1 – Project Minimum Requirements to move all requirements up front and in one place.
  • Updated submittal requirements –We updated submittal requirements to clarify which submittals are required based upon project specifics.
  • Updated infiltration testing requirements – We expanded infiltration testing requirements and made them applicable to most projects in order to be equivalent with the Stormwater Management Manual for Western Washington .
  • Reorganization of Volume 3 – We organized Volume 3 – Project Stormwater Control to consolidate general design requirements, group BMPs together, and to streamline text and figures.


For more information, visit our Stormwater Codes & Rules Update website, or contact:

Michelle Macias
(206) 684-3068