Onsite Sewage Systems

This Vital Sign helps us track progress on management of onsite sewage systems and the protection measures put in place to protect nearshore areas. Onsite sewage systems, commonly known as septic systems, are widely used around Puget Sound to treat sewage from properties not served by municipal sewers. Leakage of sewage from septic systems into Puget Sound water causes poor water quality and can lead to public health risks.


Key Vital Sign Messages

  •   Septic system for a home (WA Department of Health).
    When septic systems malfunction, improperly treated sewage can surface or move through the soil to groundwater, streams, lakes, rivers, and Puget Sound. Malfunctioning septic systems are a potentially significant contributor of harmful bacteria in freshwater and marine waterways.
  • The bacteria can accumulate in shellfish to the point that they may no longer be safe to eat and cause shellfish beds to close to commercial and recreational harvest (see the shellfish beds indicator). Harmful bacteria from septic systems also pose a health risk to swimmers (see the beaches indicator).
  • All owners are responsible for taking care of their septic systems. The twelve Puget Sound local health jurisdictions oversee management plans to help owners maintain their systems, and the Department of Health provides additional technical and financial support.
  • Marine Recovery Areas, defined by state statute, are designated where septic systems are associated with the degradation of shellfish growing areas (see the Shellfish Beds Vital Sign), marine waters listed as polluted for low dissolved oxygen levels or fecal coliform, or marine waters where nitrogen has been identified as a contaminant of concern (see the Marine Water Quality Vital Sign).
  • In Marine Recovery Areas and other designated areas, local health jurisdictions engage more directly with owners to help ensure systems are inventoried, inspected, and maintained to reduce public health risks.
  • Since 2011, local health jurisdictions have inventoried nearly 90,000 septic systems, 92 percent of which are fully documented. Additionally, more than 40,000 systems (48 percent of the inventory) are up-to-date with inspections. In part due to addressing failing septic systems, 13,838 acres of shellfish beds were reopened to harvest since 2007.

Other Resources

Articles related to sewage pollution in the Encyclopedia of Puget Sound

Contributing Partners

Mary Ramirez and Nathalie Hamel, Puget Sound Partnership
Last Updated