Grading, Drainage, and Clearing Requirements (Land Disturbing Activity)

Why is regulation of stormwater runoff important?

Stormwater runoff is rain that runs off hard surfaces, rooftops, streets, parking lots, and landscaped areas. As water runs off these surfaces, it can pick up pollutants such as oils, dirt, and fertilizers. Polluted stormwater runoff is a leading contributor to water pollution in the Puget Sound region.

Runoff can also cause and contribute to flooding. When runoff is uncontrolled, it could result in the destruction of property, harm to fish and wildlife, damage to aquatic habitats, loss in aesthetic values, and cause threats to public health due to contaminated food, drinking water supplies, and recreational waterways.

Snohomish County is committed to complying with federal and state requirements to provide effective and efficient stormwater management in our community. As part of our work, we maintain stormwater regulations that guide new development and redevelopment to minimize pollution and harmful effects of stormwater.


Where can I find the County’s Stormwater regulations?

Please visit the Stormwater and Drainage Regulations webpage for more information on the permitting process and links to associated checklists and assistance bulletins.

The County’s current stormwater and drainage requirements are found in:

Please visit our LID webpage for resources and information.

New February-March 2021:  Updates to the stormwater regulations will be considered by the Planning Commission.  A briefing occurred on February 23rd and a public hearing is tentatively scheduled for March 23rd.  Link to the Planning Commission agenda here.

Stormwater, drainage, and land disturbing activity regulations are updated from time to time. Generally, projects vest to a particular version of the regulations depending on when project applications are submitted. However, a recent Washington State Supreme Court decision and the County’s Phase I Municipal Stormwater Permit (“Phase I Permit”), issued to the County by the Washington State Department of Ecology, now require a different result.


On December 29, 2016, the Washington State Supreme Court issued a decision in Snohomish County v. Pollution Control Hearings Board related to the County’s Phase I Permit. The Court held the County’s updated stormwater regulations are not “land use control ordinances” subject to state vesting statutes. This is a significant change in the law for developments across the state.

Snohomish County is a Phase I jurisdiction under the federal Clean Water Act National Pollutant Discharge and Elimination System (NPDES) program. The County must comply with its Phase I Permit. One aspect of the County’s compliance with its Phase I Permit is the adoption of updated stormwater drainage regulations, which the County accomplished effective January 22, 2016, and which the County must further update by July 1, 2021. County documents that will be updated by July 2021 include: Chapters 30.63A and 30.63B SCC, Snohomish County Drainage Manual (Volumes I through V), and Snohomish County Design and Development Standards (Chapters 1, 5 and 11). The current county stormwater program can be reviewed on the Drainage and Land Disturbing Activity webpage.

What Does This Mean for Development Projects?

The County’s Phase I Permit requires the County to impose updated drainage regulations to projects that have not started construction as follows:

  • Approved projects currently subject to a pre-January 22, 2016, version of the County’s drainage regulations that have not started construction by July 1, 2021, must be reevaluated by PDS for compliance with updated drainage regulations the County will adopt by July 1, 2021.
  • Pending applications submitted prior to January 22, 2016, that have not been approved and thus have not started construction by July 1, 2021, must be reevaluated by PDS for compliance with updated drainage regulations the County will adopt by July 1, 2021.
  • Applications submitted after January 22, 2016 but before July 1, 2021 that have not started construction by July 1, 2026, must be reviewed for compliance with new stormwater regulations in effect on July 1, 2026.

As used above, “started construction” is defined in the County’s Phase I Permit as: the site work associated with, and directly related to the approved project has begun. For example: grading the project site to final grade or utility installation. Simply clearing the project site does not constitute the start of construction.

The County Council is considering a clarification of the Ecology definition of “started construction.” These proposed code amendments will be reviewed by County Council at a public hearing scheduled for April 7, 2021 and were reviewed by the Snohomish County Planning Commission at a hearing on December 15, 2020 (agenda here).

PDS is preparing to implement this requirement effective July 1, 2021. PDS recognizes the Supreme Court decision and the requirements Ecology imposed on the County under its Phase I Permit may impact significantly some development projects, and is evaluating ways to facilitate the permitting process to minimize that impact while fully implementing the County’s obligations under its Phase I Permit. PDS performed a detailed review of its records, followed by hundreds of site inspections, to identify potentially impacted projects. PDS sent notices to alert applicants or permit-holders that may be impacted by the July 1, 2021, started construction deadline.

Contact Us

  • If you have questions about a specific application already submitted to PDS, please contact your project manager/contact. To locate your project manager/contact, enter your project file number on our Postcard page.
  • If you are preparing to submit an application for a permit, see information on the main permitting page or visit
  • For general information about the County’s stormwater regulations, please email Ken Crossman or call 425-262-2227.