Septic Tanks

The majority of areas within the City of Mandurah are connected to the Ministers Sewer, however some areas require the on-site effluent disposal systems to be installed. The document Septic Tanks provides information on the functioning and requirements for Septic Tank systems.

Generally these systems comprise of two septic tanks and two leach drains or four soakwells. However, the type of effluent disposal system required will depend on the size of your house, soil type on the property, depth to the water table and the environmental sensitivity of the area.

In some areas, aerobic treatment units and nutrient retentive systems are necessary to ensure that phosphorous does not impact on natural water bodies. A range of systems are available, the document Approved Nutrient Retentive On-site Effluent Disposal Systems provides a list of permitted systems to choose from.

Before an effluent disposal system on your property you need to complete an Application to Construct or Install an Apparatus for the Treatment of Sewage. This form with 2 sets of detailed plans (1:100 or 1:200 scale only) of the proposed system must be forwarded to the City's Environmental Health Services Section along with the appropriate fee.

Important things to consider when considering where a septic tank system is to be located are:

• Septic tanks and leach drains must be a minimum of 1.2m away from trafficable areas
• Septic tanks must be a minimum of 1.2m from any structure
• Leach drains must be a minimum of 1.8m from any structure and 1.2m from trafficable areas
• The bottom of a leach drain must be a minimum of 1.2 m above the highest known ground water level
• Leach drains must be at least 30m away from any water course or bores used for potable water and at least 15m away from all other water courses or bores.

Decommissioning Of Septic Tanks

Under the Health (Treatment of Sewage and Disposal of Effluent and Liquid Waste) Regulations 1974, where a property has already been connected to the sewer the owner must decommission any disused septic tank or effluent disposal system at the following times:

• If there is a change of use to the premises, decommissioning must occur not more than 60 days after the day on which the change in use occurred (eg Residential to Child Care Centre)
• If ownership details change decommissioning must occur not more than 60 days after ownership of the property has changed. i.e. New owner responsible for decommissioning, not the person/s who originally connected to the sewer
• If foundations for a building on the premises are to be built closer than 1.2 metres from the system or a building is to be constructed above the system, decommissioning must occur before building works commence.

Further information and the procedure for decommissioning septic tanks is available in the document Decommissioning of Septic Tanks.