Official sources checked August 29, 2026

Snohomish County, Washington septic permits and requirements

Washington local-health-jurisdiction framework

Washington State Department of Health places property-level onsite sewage permitting and management with local health jurisdictions. Local agencies review and approve OSS siting, design, installation, repair, and operation under Chapter 246-272A WAC and may adopt local requirements that are more protective than the statewide minimums.

County reviews systems under 3,500 gallons per day

Snohomish County Health Department reviews onsite sewage designs and installations for residential properties and small businesses with design flows below 3,500 gallons per day. The department also reviews construction clearances and handles local septic enforcement and contractor certification; larger systems are regulated by Washington State Department of Health.

Licensed professional prepares the septic application

County guidance says applicants first hire a licensed professional to evaluate the site and design the system. The septic designer submits the onsite sewage permit application and proposed design to the Health Department for completeness and technical review before installation permitting can proceed.

Professional-only submittals

Snohomish County identifies several documents that may be submitted only by a licensed septic designer or professional engineer, including the onsite sewage permit application, waiver requests, and OSS as-built documents.

Construction clearance before building permit

For development on property served by septic, the Health Department reviews a Construction Clearance to ensure the building project is compatible with the existing or proposed septic system and water supply. Once approved, the Health Department notifies the applicable permitting agency so the building permit can proceed.

County certification required for septic contractors

Installers, pumpers, and monitoring-and-maintenance specialists must be certified by Snohomish County Health Department before working in the county, even if they hold a certification from another county. These county certifications are renewed annually.

Official sources

• Washington State Department of Health — Onsite Sewage Systems
• Washington State Department of Health — OSS Rule Revision
• Snohomish County Health Department — Septic Permitting
• Snohomish County Health Department — Septic Permit Steps
• Snohomish County Health Department — Septic Application Forms
• Snohomish County Health Department — Construction Clearances
• Snohomish County Health Department — OSS Certification and Licensing
• Snohomish County Health Department — Permits and Fees

SepticScope summarizes public-agency information for planning purposes. The permitting agency's current instructions control if they differ from this guide.