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On-Site Sewage Systems

On-Site Sewage System (OSS) Program

The On-site Sewage System Program has regulatory oversight for all on-site sewage systems in Whatcom County. We perform a wide variety of activities to carry out this oversight that include:

  • Site Application review for new, repaired or expanded OSS
  • Permit Issuance
  • Final Construction inspections
  • Subdivision, Boundary Line Adjustment and Conditional Use review
  • Complaint investigations
  • Enforcement of OSS Codes, e.g. Whatcom County Code, WCC 24.05 and Washington Administrative Code, WAC 246-272A
  • Survey inspections of OSS in sensitive areas
  • Homeowner education and notification regarding proper Operation and Maintenance of their OSS
  • Certification program for OSS Pumpers, Installers and Operation and Maintenance Specialists

Click on the following for more information about the OSS Program:

OSS Documents Online

OSS Program Forms

OSS Operation & Maintenance Requirement

Homeowner Inspection Certification Training

OSS Annual Fee

OSS Permit Process

OSS Loan Program

OSS Rules & Regulations

Licensed Designers

Licensed Installers

How to Obtain an Installer's License

Installer Licensing Study Guide

Licensed Operation & Maintenance (O&M) Specialists

How to Obtain an O&M Specialist License

Licensed Pumpers

How to Obtain a Pumpers' License

Pumpers' License Study Guide

Cleaning up after a Sewage Spill

Seven Ways to Save Thousands of Dollars in Septic System Repairs Brochure

Frequently Asked Questions

Should I use an additive in my septic tank?
Most additives do not have any positive effect on your septic tank. Nothing you add to your tank will improve normal bacterial action.

When is an OSS Permit needed?
An OSS Permit is needed anytime you construct, repair, replace, modify, connect to, or expand your OSS. An OSS is not required if you replace a baffle in a septic tank, fix a broken house sewer pipe, replace a pump control float, fix or replace risers, lids, or inspections ports, or replace a pump.

Can I design my own OSS?
State and County Sewage Control Regulations require that either a Licensed OSS Designer or Registered Professional Engineer design your OSS. The State issues Licenses for Designers and Engineers. See Washington State Department of Licensing website.

Can I install my own OSS after I obtain an OSS Permit?
Whatcom County code requires that all OSS be installed by a Licensed OSS installer; however, if you are the property owner and you will live in the home the OSS will serve, you can request an exemption from certification requirements. The request will be reviewed and if approved, you can install the OSS. We recommend that you hire a Licensed OSS Installer for complex systems, e.g. pressure systems or alternative systems. Developers must hire a Licensed OSS Installer or obtain an OSS Installer's License through the Health Department to install OSS on properties they plan to develop and then sell.

Do you have a copy of my OSS permit?
Health Department documents related to On-site Sewage Systems (OSS) and Drinking Water in Whatcom County can now be found online here.

To search for the documents, you must enter the property’s Property ID, which can be obtained from the Whatcom County Assessor/Treasurer Property Search website:

The Property Search website allows for searching via the Geographic ID (aka “Parcel Number”), Property Address, or Owner Name.
Please email us at if you have difficulty accessing the documents.

How do I clean up sewage that has backed up into my house?
Please see the following guidelines from the Washington State Department of Health - Sewage Clean-up.

What are some signs that my OSS is failing?
Some warning signs of a failure are:

  • Odors, surfacing sewage, soggy spots with lush green grass growth in the drainfield or septic tank area.
  • Plumbing or septic tank backups
  • Slow draining fixtures
  • Gurgling sounds in the plumbing system

If you suspect that your OSS is failing, contact us for assistance.

How can I find my septic tank?
If you have an "as-built", locating the septic tank will be easy. If one is not available you or your pumper will need to use some investigative skills. If a crawl space is available you may determine where the plumbing leaves the foundation wall and then use a probe bar to find the tank. Use caution as fiberglass or polyethylene tanks can be ruptured with a probe bar. Probing works best if the tank is not more than 1-2 feet under the surface.

If a crawl space is not available, you can sometimes use the plumbing vents located in the roof. A plumbing vent may align with the exit point of the sewer line leading to the septic tank.
If these options don't work it may be necessary to use an electronic detection device with a transmitter that can be flushed down the toilet.

What is the "reserve area"?
The reserve area is designated on your OSS Permit and is another area approved for the installation of a new drainfield in case the main drainfield fails. The reserve are must be kept clear of impermeable surfaces, e.g. buildings and pavement. If your OSS Permit was issued more than five years ago, you may need to have your reserve area redesigned to meet current code requirements.

Septic Onsite Systems - EPA
Lake Whatcom Management Program