Drainage & Land Disturbing Activity

Last Updated: March 2016

Updates to the County’s stormwater regulations

On January 11, 2016, after a public hearing, the County Council voted to approve Ordinances Nos. 15-102 (PDF) and 15-103 (PDF) to amend the County’s stormwater regulations for consistency with the Phase I Municipal Stormwater Permit ("NPDES Permit"). Under the terms of the Permit, Snohomish County’s deadline for having its new regulations in effect is January 22, 2016.

For an overview of the stormwater and drainage thresholds and new requirements, review this flow chart (PDF). The flow chart provides links (coming soon) to stormwater and drainage documents needed for project application submittals.

What has changed?

Chapters 30.63A SCC (Drainage) and 30.63B (Land Disturbing Activity) have been updated as have a number of definitions in Chapter 30.91 SCC (Definitions). Chapter 30.63C SCC (Low Impact Development) has been repealed because use of low impact development (LID) best management practices (BMPs) is no longer optional under the County’s NPDES Permit. The most significant change for consistency with the County’s NPDES Permit is that LID BMPs are now required where feasible.

Many of the technical LID BMP requirements have been removed from Chapter 30.63A SCC and relocated in the updated Snohomish County Drainage Manual (Drainage Manual) or in the updated Engineering Design and Development Standards (EDDS).

The code changes can be reviewed in Ordinances Nos. 15-102 (PDF) and 15-103 (PDF) or in the summary notices published for each ordinance: Summary Notice Ord. No. 15-102 (PDF) and Summary Notice Ord. No. 15-103 (PDF).

New Stormwater and Drainage Requirements

The following documents comprise the new stormwater and drainage requirements.

What documents do you need if you want to apply for a permit or a land use action?

In addition to the permit or land use application submittal requirements (e.g., single-family home, private garage/shop, land disturbing activity, short plat, or subdivision), documentation is required for compliance with drainage requirements. Review this flow chart (PDF) to determine what thresholds are met by your proposed project and what minimum requirements (MRs) your project must address. The flow chart will provide links to documents for projects subject to:

  • Minimum Requirement 2 Stormwater Pollution Prevention Plan (SWPPP) only;
  • Targeted Drainage Site Plan (Minimum Requirements 1-5) and a SWPPP; and
  • Construction / Full Drainage Site Plan (Minimum Requirements 1-9) and a SWPPP .

The Minimum Requirements are explained in the Drainage Manual, Volume I, Chapter 2. Guidelines for your Stormwater Site Plan (MR1) can be found in the Drainage Manual Volume I, Chapter 3. SWPPP guidance can be found in the Drainage Manual Volume I, Appendices I-F for small projects (see SCC 30.63A.810 to determine if your project qualifies as a small project), or in Volume II, Chapter 3 for Construction / Full SWPPP instructions.


Additional Documents:



The federal Clean Water Act (CWA) includes a permit program, the National Pollutant Discharge Elimination System (NPDES), that accounts for stormwater runoff that collects in municipal separate storm sewers (MS4s) and enters surface waters. The Environmental Protection Agency (EPA) developed rules to implement the regulations and established two phases, Phase I and Phase II, for the municipal stormwater permit program. The Washington State Department of Ecology develops and administers the NPDES municipal stormwater permits in Washington State.

The Phase I NPDES permit regulates discharges from municipal separate storm sewers owned or operated by Clark County, King County, Pierce County, and Snohomish County; and the cities of Seattle and Tacoma. The Phase II Municipal Stormwater Permit rule extends the coverage of the NPDES program to certain small municipal separate stormwater sewer systems (MS4s).

For more information, please visit the Washington Department of Ecology website.

For more information about the adopted rules and training opportunities, please visit the following websites: