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FAQ - Septic Systems / Wells / Plumbing

Who should I contact for septic system, drainfield or well questions?

Call the Environmental Health Program at (360) 867-2673

How do I get my site approved for a septic system?

If your site will require on-site sewage disposal, you will need to contact a certified on-site sewage (septic) system designer. Thurston County Environmental Health keeps a list of certified designers in the area. State-licensed engineers with expertise in civil or sanitary engineering and state-registered sanitarians also are qualified to design on-site sewage (septic) systems.

The next step is to seek "Conditional Site Approval."  Your sewage system designer must submit:

  • Master Application (form MA 001) and Supplemental Application (Form SA 016)
  • Site Plan (five copies) (Form SA 016 will tell you what to include on your site plan)
  • On-Site septic system design (three copies) (Form SA 016)

A county Environmental Health Specialist will visit your building site to do a soils evaluation. Typically, your sewage system designer will need to dig two test holes in the proposed primary drainfield area and one hole in the proposed reserve drainfield area before the inspection. The holes should be at least 6 feet deep (unless the water table or a restrictive layer is shallower than 6 feet), at least 2 feet wide, and sloped to allow access into the hole. The designer should clearly flag each hole.

Other county reviewers may verify other information that you or your agent submitted as part of your site plan. They may check major topographic features, vegetation coverage, location of critical areas (shorelines, flood plains, wetlands, steep slopes, etc.), and proposed access to the site. To help the reviews find your lot and compare your site plan with the actual site, please make sure that you clearly flag the property corners and the location of proposed access point(s) to the project site.

What steps are involved in the design review stage? When do I get my septic system permit?

 Environmental Health staff will check design information for compliance with state and local regulations and technical requirements. The environmental health specialist will tell you and your designer if any changes to the initial sewage system design are necessary. Your designer is responsible for submitting revised design information to Thurston County Environmental Health.

When your on-site sewage (septic) system design has been approved, the reviewer will notify your case manager in the Permit Assistance Center. The case manager will add this approval to your project file. When all departments have approved your proposal, you will receive a Conditional Site Approval letter approving an on-site sewage (septic) system design for your property and establishing written conditions for further site development.

After meeting any requirements explained in the Conditional Site Approval letter and paying the permit fee, you will receive an On-site Sewage (Septic) Installation Permit to construct your system. When the system is installed, the sewage system designer must call Thurston County Environmental Health for a final inspection and submit “as-built” drawings (drawings that show how your system is actually constructed). After Environmental Health accepts the as-built drawings, you will receive an Operational Certificate with conditions for ongoing operation and maintenance of your system. You may now begin using the system. You must follow the conditions listed in your certificate to stay in compliance. Most Operational Certificates must be renewed every four years or before the expiration date.

What if my site is served by a public sewer system?

If your site is served by a public sewer system, you do not need to get conditional site approval as described above. Instead, you will list your sewer provider on your residential building application (application SA 001).

Contact Us

Thurston County Building Development Center, 2000 Lakeridge Drive SW, Olympia, WA 98502-6045.
Phone: (360) 786-5490. TTY/TDD call 711 or 1-800-833-6388 E-mail: permit@co.thurston.wa.us.


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