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Public Health - Seattle & King County

Inspecting your septic system

Protect your inve$tment - It's the law! Routine maintenance keeps your septic system and surrounding environment healthy!

How will inspecting my septic system benefit me?
  • Protects your underground investment against a premature failure
  • Saves money: replacing a failed septic system can cost up to $15,000
  • Protects your family, environment and community from sewage spills
  • Provides assurance: routine maintenance of your septic system is essential, just like taking care of a car or bike

Routine maintenance can lengthen the life of your septic system. Contact a certified On-site System Maintainer to inspect and monitor your system on a regular basis. A certified OSM has two or more years of experience, has completed a monitoring and maintenance class and has passed an exam given by Public Health – Seattle & King County.

When should I call an On-site System Maintainer?

The frequency of inspections depends on the type of your septic system.

Gravity systems:

It is the owner's responsibility to inspect their systems either themselves or by a certified Pumper or On-site System Maintainer

  • Annually with a garbage disposal
  • Every three years without a garbage disposal

Pressure Distribution systems:

  • Annually with a garbage disposal
  • Every three years without a garbage disposal
  • If your system includes an Aerobic Treatment Unit (ATU), the ATU is also inspected with the following schedule:
    • Every 6 months – basic inspection
    • Annually – full inspection

Mound, Sand Filter, Upflow Sand Filter or Sand Filter to Mound systems:

  • Every 6 months (Glendon BioFilter only)
  • Annually
  • If your system includes an Aerobic Treatment Unit (ATU), the ATU is also inspected with the following schedule:
    • Every 3 months – basic inspection
    • Annually – full inspection
What happens during an inspection?

The On-site System Maintainer (OSM) will inspect three sections of your septic system: the primary treatment unit, septic and pump tank and the reserve area. Read Section IV of your Monitoring Report for comments and recommendations made by your OSM.

Sample Monitoring Reports your OSM will use:

  • Gravity or Pump to Gravity
  • Pressure Distribution, Sand Filter, Mound
  • Glendon BioFilter
  • Aerobic Treatment Unit (ATU)

You are not required to be present during the visit, although it is recommended by Public Health. The OSM will give you a copy of the Monitoring Report and submit a copy to Public Health.

If an uncertified OSM inspects your system, the Monitoring Report will be invalid. A certified OSM must be contacted to inspect your system.

What should I do with my copy of the Monitoring Report?

Keep it in your personal septic system file as part of the system's history. The file should be given to future owners.