2019-2024 Stormwater Update/Current Requirements


Updated: July 2021

July 1, 2021 - effective date for new requirements

The County has adopted new stormwater requirements. The updated code and Drainage Manual are effective as of July 1, 2021. The changes are summarized here:


The National Pollutant Discharge Elimination System (NPDES) permit program addresses water pollution by regulating point sources that discharge pollutants to waters of the United States. Created in 1972 by the Clean Water Act (33 USC § 1251), the NPDES permit program authorizes state governments to perform many permitting, administrative, and enforcement aspects of the program. In July 2019, the Washington State Department of Ecology issued a new Phase I Municipal Stormwater Permit as authorized under RCW 90.48 and the Clean Water Act. This Phase I Permit is valid until mid-2024 at which time Ecology will issue an updated permit. The 2019-2024 Phase I Municipal Stormwater Permit, including appendices, can be reviewed on Ecology’s website here.

“Started Construction” Requirements 

The County has completed a distinct code project to implement the “started construction” requirement from special condition S5.C.5.a in the Phase I Municipal Stormwater Permit. Development projects with complete applications submitted to the County before January 22, 2016, but have not reached the “started construction” phase by July 1, 2021, are subject to these new requirements.  These projects are required to revise drainage plans for the development site as necessary to meet the newly updated regulations. The County has sent notifications to these applicants.  The requirements are in SCC 30.70.310, including the definition for “started construction.” 

These are rolling requirements out into the future with deadline dates that coincide with the statutory effective dates for local stormwater updates under the Phase I Permits.  Projects with complete applications submitted prior to July 1, 2021, that do not reach the “started construction” phase by July 1, 2026, will also be subject to these requirements in SCC 30.70.310.  

Click here to view a document summarizing the revised Snohomish County definition for “started construction” for the Phase I Stormwater Management Permit.

Adopted Enforceable Documents

Changes to SCC 30.91 Definitions 

SCC 30.63A  Drainage  

SCC 30.63B  Land Disturbing Activity

Snohomish County Drainage Manual

Snohomish County Engineering Design and Development Standards (EDDS) (Chapters 1, 5 and 11)

Additional resources and FAQs are located here.

For information about low impact development (LID), click here.

Next Steps

The Washington State Department of Ecology will take action to modify the Phase I Permit, Appendix 10, Part 1.  This modification acknowledges that the County’s stormwater program is equivalent to Ecology’s 2019 Stormwater Management Manual for Western Washington. Ecology’s action will follow procedural requirements in WAC 173-220-190. Ecology will establish the schedule for this modification process. Ecology’s action to modify the Phase I Permit is appealable per WAC 173-220-225 – the scope for appeals is limited to the modification.

Attn: Terri Strandberg, Principal Planner

Snohomish County Planning and Development Services

3000 Rockefeller Ave., M/S 604

Everett, WA 98201