What is decommissioning?

Decommissioning means that all septic tanks and leach drains are pumped out by a licensed liquid waste contractor. All empty septic tanks and leach drains must be either removed or have their lids and bases broken and filled with clean sand.

Once a sewer connection is available to a property that has historically had an effluent disposal system, it must be connected within five years of the Water Corporation advising of its availability.

If the property is sold, it has to be connected within one year of the settlement date.

Alternatively, if a new effluent disposal system is being installed to replace an old one; or there is a redevelopment that will result in the development encroaching over the effluent disposal system; the old effluent disposal system needs to be decommissioned as part of the process.

Redundant effluent disposal systems must be ‘decommissioned’ to prevent them from collapsing in the future and possibly causing damage or injury.

When to decommission an effluent disposal system

The Shire strongly recommends that onsite effluent disposal systems be decommissioned soon after a property is connected to mains sewage for the decommissioning can be forgotten and create a problem in the future.

Under law, septic tanks must be decommissioned:

  • Not more than 60 days after ownership of the property has changed. New property owners are responsible for ensuring that septic tanks are decommissioned and are advised to obtain proof. This process is often negotiated during property settlement
  • If the foundations for a building on the premises are to be built closer than 1.2 metres from the septic tank, or a building is to be constructed above it
  • Decommissioning must occur before any building works commence
  • Within 60 days if there is a ‘material change of use’ of the property. For example, if a residence is turned into a business, the system must be decommissioned not more than 60 days after the change of use has occurred.

How to decommission an old septic system

Septic tanks and leach drains must be completely emptied by a licensed liquid waste contractor.

Empty septic tanks, leach drains should be completely removed from site if possible. If it is not possible, the lids must be removed and the bottom of septic tanks broken up and back-filled with clean fill.

If the area where an effluent disposal system is to be decommissioned and have a structure erected in its place, you need to consult a structural engineer for advice.

More information and contact

For more information on decommissioning a septic tank please contact the Shire’s Health Services on 9290 6742 or email Shire@mundaring.wa.gov.au.