Wastewater treatment system
How a septic tank/wastewater treatment system works
If you reside on a rural property which is not connected to a sewer system, your property will require an onsite wastewater treatment system.
You can check with Western Water or City West Water to see if your property is on a main sewer.
There are two main wastewater treatment systems:
- a standard septic system
- a treatment plant
Both are used for the treatment of wastewater generated by toilets, the kitchen, bathrooms and laundries from your household. Treatment plants generally produce a cleaner, low odour effluent.
When your household wastewater flows into the wastewater tank most of the solids in it sink to the bottom. Over time, microorganisms will decompose these solids into sludge and gasses. The sludge builds up on the bottom of the tank while the gasses and other lighter materials rise to the top of the tank and form a floating layer of scum. The wastewater left in the middle is released to a disposal field set aside on your property.
All effluent must be disposed via sub-surface irrigation and, if from a treatment plant, the effluent must be evenly distributed via pressure compensated piping.
Applying for a permit
You must apply to our Environmental Health Office for permission to install or alter a septic tank system or other domestic wastewater treatment system.
Applications must include the following:
- completed and signed Application for Wastewater Treatment System Under the Environmental Protection Act
- a site plan
- location of all buildings or proposed buildings, water tanks, swimming pools, driveways, excavations, stormwater drains, water pipes, easement drains, streams, dams and water courses
- fall of land in vicinity of wastewater disposal area
- position of septic tank and layout of wastewater disposal area
- house floor plans
You may need to have a Land Capability Assessment (LCA) of your property to decide the most suitable system to treat your wastewater. If this is required a copy of the report will also need to be included with your permit application. You may enquire with our Environmental Health Services as to whether this will be required for your property.
After receiving the Permit to Install
As the wastewater treatment system is installed, you or your plumber must contact our Environmental Health Services to arrange progress inspections.
A 'Permit to Use' will be issued once the system is installed, all necessary inspections completed and the plumber's compliance certificate submitted. A wastewater treatment plant must not be used until the 'Permit to Use' has been issued.
Managing onsite wastewater systems
Septic tank systems do not have an unlimited life span, although you can expect to have many years of service from them. Responsibility for managing an onsite wastewater system lies with the property owner. A properly managed wastewater system will assist in prolonging the life of the system and prevent it from a premature failure resulting in a public health risk to the occupants and surrounding environment.
Some systems such as treatment plants must be regularly maintained by a professional service technician. The maintenance reports must be forwarded to our Environmental Health Services as per the original 'Permit to Use'.
Looking for more information
For further information on the installation, maintenance or alteration of wastewater treatment systems, please contact our Environmental Health Services on 03 9747 7200 or firstname.lastname@example.org.