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Wastewater

Where deep sewer is not available to a property, an onsite wastewater disposal system must be installed. Several systems are approved for use in WA. For more information on the different types of systems, refer to the Department of Health WA website.

Several factors must be considered when choosing the appropriate system and location for your property. The main factors include the available space to accommodate the system and the local soil conditions, including the depth to groundwater.

Refer to the Guidelines for the Installation of an Apparatus for the Treatment of Sewage information sheet for further information. An onsite wastewater application form can be downloaded here.

Under the Government Sewerage Policy 2019, a site and soil evaluation is required for all applications to install a wastewater treatment system unless otherwise except by the Shire Environmental Health Officer. Please refer to the Department of Health WA website for further information.

Application and approval

Prior to installing a new or altering an existing onsite wastewater system, an application must be lodged with the Shire Environmental Health Officer.

Click here to download the ‘Application to Construct or Install an Apparatus for the Treatment of Sewage’ form.  

Once an application has been received, the site and system will be assessed for suitability and if all requirements are satisfied, an ‘Approval to Construct’ will be issued. 

After the system has been installed, and prior to the system being covered with soil, the installer must contact the Shire Environmental Health Officer to arrange for a final inspection to ensure the system has been installed as per the approval. Within 7 days of the final inspection taking place, an ‘as-constructed’ plumbers plan must be submitted to the Shire. Once the final installation of the system has been approved, then a ‘Permit to Use’ will be issued to the property owner. Please note that it is an offence to occupy a house or use a system without a ‘Permit to Use’ having been issued.

Maintaining a system

To ensure optimum operation of a septic system, a few basic maintenance items must be regularly attended to:

  • Alternate the leach drains by switching the diverter device on a regular basis. It is recommended that each leach drain is rested every six to 12 months.
  • Ensure septic tanks are pumped out on a regular basis. The  timing will depend on the usage, but on average for a two-bedroom house it is recommended that the tanks be pumped out every eight to nine years. Please note that only licensed liquid waste contractors can pump out septic tanks. 
  • Ensure any alternative treatment system is regularly serviced by a qualified agent as per the approved maintenance agreement and that the agent submits the service reports to the Shire on a regular basis.

Soil Types and the Required Systems

Most lots within the Shire are in an area where the soil is either clay/loam or light clay, but more likely medium/heavy clay. In either circumstance a Secondary Treatment System or a Flat Bed (ETA) system is considered the most appropriate solution for managing wastewater.

However, if a standard system (septic tank/s connected by divertor to 2 leach drains) is being considered then depending on the soil type:

Clay/Loam or Light Clay

A fully inverted standard system consisting of a primary treatment system (septic tank) + 2 leach drains can be considered if a report is provided with the septic application that confirms:

      • The soil type clay/loam or light clay
      • Leach drains are to be fully inverted
      • Leach drains are a minimum of 3.6m apart
      • Sand pad extends a minimum of 1m beyond the side and ends of leach drain to the start of the clay retainer/bund
      • Sand pad is retained/bunded by clay minimum of 1m wide, keyed into the sand pad for stability
      • Note: the size of the system will depend on the number of bedrooms the proposal will have, plus the inclusion of a spa or any other wastewater producing premises on the property, eg a studio or shed. The sizing of the system is to be calculated by the plumber, but the Shire’s Environmental Health Officer will double check the calculations when the Application to Construct or Install an Apparatus for the Treatment of Sewage is received.

If the calculations are found underestimate the lengths of leach drains to be installed the system will need to be resized.

 

If the installation of a standard system below natural ground level is proposed then the requirement would be for 4 leach drains to be installed, installed in accordance with the below diagram. The lengths of the leach drains is calculated on the width of the fill.

Medium/Heavy Clay

      • Primary treatment systems are not suitable for this soil type and an STS/ATU or ETA (Flatbed leach drain) system will be required.