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Septic Tanks

Septic tank applications & decommissioning

The Shire's Environmental Health Services section work to ensure onsite wastewater systems do not pose environmental or public health threats. To achieve this we attempt to ensure that all on-site effluent disposal systems are installed, operated and maintained in accordance with legislative requirements to prevent transmission of disease and to produce the best possible environmental outcomes particularly with respect to our waterways.

System installations are only permitted with the approval of the Shire of Irwin and the Department of Health, WA. For the application form click here. This includes both combined effluent disposal systems at premises where sewer is not available, and also greywater re-use systems which may be installed in either sewered or unsewered areas.

The Shire of Irwin will only consider applications for installation of an on-site effluent disposal system where that system has been approved for use in Western Australia by the Department of Health.


When a developed property is connected to sewer, usually under the infill sewerage program, any onsite effluent disposal systems such as septic tank and leach drain/soakwell systems will eventually require decommissioning. This requires that the contents of the tank are pumped out by an approved contractor and the system either removed or backfilled. If the system can't be removed, the tanks should be pumped out, the bottom of the tanks broken up and the system backfilled with sand.

As there are costs involved in both decommissioning a septic tank and connecting to sewer, householders are not automatically required to decommission tanks when they connect to the sewer. Under the Health (Treatment of Sewage and Disposal of Effluent and Liquid Waste) Regulations 1974 decommissioning is required when:

  • The property is sold
  • The use of the development changes e.g. from a residence to a child care centre
  • Building extensions may encroach on minimum setback requirements for the system

Septic tanks which have not been decommissioned must not be paved or built over without approval from the Shire.

The Shire requires notification to be forwarded when a system has been decommissioned. Please forward a letter to the Shire with a copy of the certification from the liquid waste contractor.

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