Snohomish County, WA Environmental Rules: Stormwater Management (2026)
Key Facts
- Site plan trigger
- 2,000 sq ft new/replaced hard surface
- Full 9-requirement trigger
- 5,000 sq ft hard surface or 0.75 acre cleared
- Land disturbance trigger
- 7,000 sq ft disturbed
- Noncommercial penalty range
- $300 to $3,000 base
- Commercial penalty range
- $600 to $6,000 base
- Repeat violation penalty
- Base penalty doubled
Summary
Unincorporated Snohomish County requires a stormwater site plan and drainage review once a project adds 2,000 square feet of new or replaced hard surface, or disturbs 7,000 square feet of land, under SCC chapter 30.63A. Discharges that violate water quality standards draw monetary penalties up to $3,000 for residents and $6,000 for businesses under chapter 7.53.
Unless an exception under SCC 30.63A.210 applies, new development projects shall comply with minimum requirements 1 through 5 (SCC 30.63A.400 through 30.63A.525) for the new and replaced hard surfaces and the land disturbed if the new development will: (a) Result in or add 2,000 square feet or greater of new, replaced or new plus replaced hard surface area; or (b) Cause land disturbing activity of 7,000 square feet or greater.
Official source re-checked September 8, 2026: no newer edition of the code had been published (publisher’s edition: current through legislation passed August 12, 2026).
Full Breakdown
54 SCC, together with the county's Drainage Manual, Engineering Design and Development Standards, and the WSDOT Highway Runoff Manual, constitute the county's stormwater regulations, so the rules run across several chapters rather than one page of code. 300: unless an exception applies, a new development project must comply with minimum requirements 1 through 5, covering a stormwater site plan, erosion control, and best management practices, once it adds 2,000 square feet or more of new, replaced or new-plus-replaced hard surface, or causes 7,000 square feet or more of land-disturbing activity.
Projects that add 5,000 square feet of new-plus-replaced hard surface, convert three-quarters of an acre to lawn or landscaping, or convert two and a half acres to pasture must meet all nine minimum requirements, including permanent flow control and treatment facilities built to the county's Drainage Manual. 310, including a 50-percent-of-assessed-value trigger for commercial and industrial remodels. 070. 180 requiring correction of a violation.
Violations & Fines
SCC 7.53.190 lets the director impose a monetary penalty on the person responsible for a discharge violation, scored under the five-criteria matrix in SCC 7.53.192. For noncommercial violations, SCC 7.53.195 sets base penalties from $300 at 0-2 points up to $3,000 at 13 or more points; SCC 7.53.197 sets commercial base penalties from $600 up to $6,000 on the same point scale. Repeat violations or repeat violators double the base penalty, and the county can add its investigation and lab costs on top of the fine, with all responsible parties jointly and severally liable.
Frequently Asked Questions
When does a Snohomish County project need a stormwater site plan?
What counts as an illegal discharge under the county's stormwater code?
How much is the fine for a stormwater violation in Snohomish County?
Which manual do Snohomish County drainage rules point to?
Sources & Official References
Other rules in Snohomish County
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