Safe and effective effluent disposal systems are important for the health of any community. The Shire of Mundaring Health Service approves most on-site effluent disposal systems for developments where deep sewerage is unavailable.

The majority of the Shire relies on on-site effluent disposal through the use of conventional septic tank disposal systems or Alternative systems. Clay soils, site gradients, water bodies, seasonal perched water tables and designated surface water catchment throughout most of the Shire place considerable constraints upon the location and design of effluent disposal systems.

The cost of suitable on-site effluent disposal may add to development costs and reduce the available useable area of the land.

Conventional Effluent Disposal

These consist of two septic tanks (or one larger baffled tank) that treat the effluent to a primary level and the effluent is allowed to drain into the ground by way of two leach drains. Only one leach drain is used at a time so that the other may be able to dry out and “rest”. This extends the life of the leach drains considerably and reduces the risk of the system failing. The valve in the diverter box does need to be switched every 12 months or so.

Conventional effluent disposal systems in many cases are the simplest and cheapest option, however in many cases there are environmental constraints that make their use inappropriate.

Conventional effluent disposal systems also come in a variety of materials including traditional concrete, plastic as well as galvanized metal leach drains. Each has their own characteristics and needs to be carefully considered before installing them.

Alternative Treatment Units

These fall into two main categories, these being:

1.      Aerobic Treatment Units: these consist of a multi tank or multi chamber design that treats the effluent to a tertiary level that is near to drinking water level. They more intensively treat the effluent and different manufacturers use different methods to achieve the same basic outcome. Instead of discharging the effluent to leach drains, the effluent is irrigated out through 150m² of irrigation area that can be used to irrigate the garden (please note that irrigation onto edible crops is not permitted). Due to their mechanized means, ATU’s are required to be maintained on a regular basis by an authorized service technician. The list of authorized service technicians can be found located right in Related Links.

2.      Nutrient Removal Systems: These consist of conventional septic tanks that are coupled to leach drains that have been specially modified into a “cell” that is plastic lined on the base and filled with a modified soil mix designed to bind up nutrients such as Nitrogen and Phosphorus.

Alternative Treatment Units are by their design well suited to properties that have environmental constrains about them. The list of approved manufacturers can be found located right in Related Links.

Greywater Reuse

Greywater is defined as any effluent with exception to waste originating from the toilet. In recent years greywater reuse has enjoyed increasing popularity, however it needs to be done with some care so as to prevent pooling or possibly spreading of disease. The practice of using a pipe from a washing machine or similar has been banned by the state government and greywater reuse needs to be done by an approved means.

A septic tank application needs to be submitted to the Shire of Mundaring so that it can be assessed for the expected volume, the location of any existing on-site effluent disposal systems, setbacks to buildings and boundaries as well as ensuring the irrigation area or trenches are large enough to handle the expected flow of greywater. There is a list of approved greywater systems and they can be found located right right in Related Links. 

More general information can be found relating to on-site effluent disposal system can be found at the Department of Health’s.

Septic tank application forms can be obtained from here. Please note that the State Government often varies the application fee every July.

For information on deep sewerage contact:
Water Corporation Sewer Connection Info Line
T: 13 13 95.

For further information regarding effluent disposal please use the Contact Us form.