Licensed On Site Sewage Installers

Only licensed On Site Sewage Installers that have a license in Whatcom County may install On Site Septic Systems (OSS) in Whatcom County. (See Homeowner OSS Installation Exemption Application process below)

A basic study guide can be purchased from the WCHD or printed from the Installer Study Guide Links to the right.

You must score 70% or higher to pass the test. Whatcom County Health and Community Services staff will correct the test and notify you of your score.  Tests may only be administered once per day, per person.

The Installers test is valid for 90 days. After receiving a passing score, you have 90 days to complete the licensing/application requirements. Any attempt to become licensed after 90 days will require a new test be paid for and passed.

Upon passing, the owner or appointed primary installer of the company must complete the application for license and pay an initial licensing fee. 

Verification of L&I license and bonding (minimum of $6,000) must also be provided.  In order to be in compliance with RCW 18.27 Registration of Contractors, you must be licensed as a general contractor or have a sanitation or side sewer specialty license.  

Annual employment verification must be provided for a primary installer if not an owner of the company.  If part owner, and not listed on the L&I verification page, written confirmation is needed to avoid annual employment verification.

Call (360) 778-6000 for test and licensing fees.

For employees of a licensed installer, annual verification of employment must be provided from the company he works for stating he is an installer for their company and covered under their bond.

The installer’s license will expire on December 31.  Fees are not prorated.  An invoice for renewal is generated at the end of each year.

Licensed installers or their licensed supervisors are required to provide three continuing education units (CEUs) in three years, in their field.  This verification must be provided no later than December 31st of each third year of being licensed.  A person may take as many hours as they wish and it can be applied to future years, not to exceed three years.

Come January 31st, if you fail to pay your renewal fee or provide a copy of your bond (if expired), or following the third year of being licensed, you fail to provide verification of CEUs for each licensee, your license will not be renewed and will have expired effective December 31st.

If you want to be licensed once again, all testing, application and fees must be completed again to be reinstated.

An installer whose license has been revoked shall be ineligible to reapply for recertification until 60 days have passed from the date of revocation of the certificate.

Homeowner OSS Installation - Exemption Procedures

As per Whatcom Code 24.05.140 Installation, Whatcom County Health and Community Services shall require certified installers to construct an On Site Sewage System.  However, Whatcom County Health and Community Services may exempt OSS installers from certification requirements if all the following conditions are met:


  • The OSS installer owns or has a beneficial interest as a contract purchaser of the land on which the OSS is to be installed; and
  • The OSS is either located on the same lot as the residence or situated on adjoining property controlled by the owner and legally listed as an encumbrance; and
  • The OSS installer will reside in or use the building served by the OSS: and
  • In addition, people engaged in the business of buying, selling, and construction homes or land shall not qualify for the certification exemption.

 To apply for the OSS Installer exemption:

  • Complete the OSS installer exemption application
  • You must provide a document from your designer stating they will conduct phased inspections and provide a record drawing prior to Whatcom County Health and Community Services conduction a final inspection.
  • You must provide a detailed construction plan on how you plan on installing all components of the OSS.  You must include a list of the tools and equipment that you will be using for the OSS installation.