Designing and building an onsite sewage system (OSS) on your property can be a lengthy process. State and local rules and regulations require that you first hire a licensed professional who will evaluate your site, design a system, and complete the permit application process with our office.
The Snohomish Health District reviews septic system designs for single family homes and small businesses (systems less than 3,500 gallons per day). The Washington Department of Health enforce regulations for larger sewage systems in Snohomish County.
Septic permit services
The Snohomish Health District provides professionals and residents in the county with the following septic permit services:
- Field and regulatory review of proposed onsite sewage disposal systems
- Drainfield repair designs for owner-occupied residences
- Operational reports for existing systems
- Complaint investigations and enforcement
- Certification and licensing of septic installers, pumpers and monitoring and maintenance specialists within Snohomish County
- Technical assistance to the general public
Septic permit process steps
- You must hire a septic system designer or professional engineer to evaluate your property. The licensed septic professional will submit your on-site sewage application and design to the Snohomish Health District
- A sanitarian from the Snohomish Health District will then review your property with the application and design to make sure they comply with state and local regulations
- If your design is not approved, you will receive a letter of explanation and may submit a redesign after addressing the outlying issues
- Once your design and application are approved, you will be mailed an application approval that will be valid for 2 years. You can renew the approval for an additional 2-year period from the system designer, with application and payment of a renewal fee, and review and approval from the Snohomish Health District)
- Hire a certified installer to request the permit be issued for installation.
- A designer must inspect the completed installation and submit an as-built to the Snohomish Health District
- A sanitarian from the Snohomish Health District will perform and approve a final inspection
Constructing your on-site sewage disposal system
When constructing an on-site septic system in Snohomish County, please be aware of the following rules and regulations:
- A septic application approval is not a permit for installation of a septic system. Permits for new structures or residences are not issued until the city or county building permit is issued
Note: If the building permit is withdrawn, revoked, or expires, the installation permit will no longer be valid.
- If an individual water supply such as a well is proposed, you may be subject to the requirements of House Bill 2929, the Growth Management Act (PDF), Section 63, regarding the demonstration of an adequate and potable water supply
- If the Application for an Individual Water Supply Site Inspection is submitted concurrently with the Application for an Onsite Sewage Disposal Permit, the fee is less than if it is submitted on its own
Sizing your septic system
When sizing conventional and alternative onsite sewage disposal systems for single family dwellings, please note the following information from Snohomish Health District's policy:
To determine the total daily flow for single-family homes with:
- 1 to 3 bedrooms, use 150 gallons per bedroom per day
- More than 3 bedrooms, use 120 gallons per bedroom per day
To review the entire Interpretation of Bedroom and Daily Flow Determination Policy, click here.
Application rates shall be determined according to soil texture type as outlined in WAC 246-272A and the Environmental Protection Agency manual.
The Minimum Land Area Requirement (WAC 246-272A) requires that minimum gross land area exists for a unit volume of sewage (450 gallons per day). Therefore, an onsite sewage disposal system application to create a new lot shall designate an area for at least a three-bedroom single-family dwelling. Note: This regulation has been in effect since July 1984.
Potential bedrooms are considered bedrooms regardless of the placement of closets, windows, and doors, or the width or location within the structure. Rooms that are considered potential bedrooms include, but are not limited to:
- Offices and studies
- Hobby, sewing and exercise rooms
- Unfinished rooms
- Bonus rooms
The Snohomish Health District typically does not count rooms such as living and dining rooms, storage areas, closets, and utility rooms as potential bedrooms.
Septic permit fees
Fees for septic permits vary based on the size and type of on-site sewage system you need for your property. See the full Land Use Fee Schedule on the Permits and Fees page.