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Wastewater
Onsite sewage treatment and disposal systems are required on properties where deep sewer is not available. Onsite septic systems can be conventional systems, aerobic treatment units, alternative treatment systems or waterless/composting toilets.
Before installing any onsite system, an approval for the installation must be granted. It is an offence to install and use a wastewater system without an approval and ‘Permit to Use’ from the Shire.
All applications are to be accompanied by a soil report showing the suitability of the site for onsite wastewater disposal. A list of contractors that may be able to assist with your application can be found here.
Details of fees and other relevant information can be found in this guideline and on the application form.
Standard septic systems
Conventional or standard septic systems incorporate two septic tanks and a pair of drainage receptacles such as leach drains or soak wells. The most common types of septic systems are usually constructed of precast concrete however plastic options are also available.
All tanks and drains are to be on the list of approved wastewater systems, published by the WA Department of Health.
Some information which may assist when preparing an application to install a standard septic system for a dwelling:
- Primary tanks are 1520mm in diameter and secondary tanks are 1220mm in diameter for standard precast concrete tanks. The size of plastic tanks vary;
- Wastewater flows through from the secondary tank through a diverter box to either leach drains or soak wells;
- Soak wells (1200mm in diameter x 1500mm depth) are only approved for use in sandy soil;
- The length of the leach drains is dependent upon the number of bedrooms, the type of soil and the manufacturer of the leach drains. This guide from the WA Department of Health will assist in sizing leach drains;
- Minimum clearances:
- Base of leach drains to be a minimum of 1.2m from the highest known water table;
- Clearance from base of leach drain to any impervious or impermeable clay in the disposal site is to be determined in consultation with an Environmental Health Officer;
- 1m between septic tanks;
- 1.2m from the septic tank to any building or boundary;
- 1.8m from any leach drain or soak well to any septic tank, any other leach drain or soak well and any building or boundary;
- All drainage areas are to be situated a minimum of 30m from any well, stream or bore intended for human consumption, a minimum of 6m from any sub-soil or open drainage channel;
- If the drainage area does not naturally fall from the tanks or if leach drains are inverted due to site conditions, a pump tank may be required. The pump tank shall have a minimum capacity of 1200L and is to be fitted with both a visual and audible warning device;
Secondary treatment systems
In most cases, conventional septic systems are adequate however in certain cases the Shire may require the installation of a system which produces effluent of a higher quality. Secondary treatment systems previously known as Aerobic Treatment Units (ATUs) are wastwater treatment systems that produce treated effluent of secondary standard, i.e. 20mg/L of Biochemical Oxygen Demand (BOD), 30mg/L of Total Suspended Solids (TSS) and 10dfu/100mL of Escherichia coli.
Secondary treatment systems may be required in environmentally sensitive areas or due to specific site conditions. Approved secondary treatment systems have been certified to Australian Standard AS1546.3 and approved by the WA Department of Health. The conditions of approval can vary between designs so it is best to discuss these with an authorised person or distributor.
Secondary treatment systems have specific installation and maintenance requirements. Maintenance of a secondary treatment system must be through an authorised person and evidence of a maintenance agreement must be presented to the Shire with the application to install.
Other types of effluent disposal systems
Greywater systems
Installation of a greywater system requires Shire approval. To apply to install a domestic greywater system, it is helpful to be familiar with the Code of Practice for the Reuse of Greywater in Western Australia.
Greywater systems are to be on the Department of Health list of approved systems.
Applications are to be submitted for all greywater diversion devices or greywater treatment systems.
Alternative treatment systems
These systems function like a conventional system but provide an alternative to a standard septic tank and leach drain system. Some alternative treatment systems also provide additional treatment at the disposal area which may assist with the removal of nutrients from the wastewater.
The alternative wastewater treatment system industry is growing rapidly and in the last few years there have been some innovative systems approved by the Department of Health. Like secondary treatment systems, an authorised installer is required for the installation. The Department of Health publishes the list of approved alternative treatment systems including contact details for each system.
Effluent disposal for commercial proposals
Commercial installations have specific requirements. Most commercial applications are referred to the Department of Health for approval. The Department of Health provide guidance on applications for a commercial onsite wastewater system. The Supplement to Regulation 29 and Schedule 9 provides specific wastewater loading rates for various commercial developments.
Septic plan search
If you would like a copy of the original septic plans for your property, please complete the septic search application. Shire officers will endeavor to locate plans as requested, however you are advised that the search fees are non-refundable if for any reason the plan is unable to be located.
