A large number of properties in the Toowoomba Regional Council area are not connected to a reticulated sewerage system. The treatment and disposal of all wastewater generated on these properties must be undertaken by an on-site sewerage facility.
On-site sewerage facility (OSSF)
An on-site sewerage facility is any system that stores, treats and disposes of household wastewater on the property. Poorly sited or maintained on-site sewerage facilities can impact public health and the environment. The owner of the facility is responsible for ensuring the system is maintained and functioning properly.
The disposal of effluent (treated sewage) may occur:
- On the property on a designated area (called a land application area)
- Off the premises by a common effluent drainage system
- Off the premises by collection from a holding tank by a council-approved liquid waste carrier.
A common effluent drainage system is where two or more premises have their wastewater combined (usually after primary treatment) and transported to a common land application area independent of premises where the wastewater was generated.
Larger onsite systems with over 20 equivalent persons require ERA 63 approval and further monitoring from the Department of Environment and Heritage Protection.
Types of on-site sewerage systems
Treatment systems for household wastewater include:
Conventional domestic sewage treatment plants (secondary treatment or better)
- Activated sludge system
- Biological trickling filter system
- Extended aeration system
- Aerated/aerobic sand filter system
- Effluent may be disposed of via trenches, surface or subsurface irrigation
Septic tanks (primary treatment)
- All-waste septic tank (all household wastewater)
- Black water septic tank (toilet, urinal and bidet wastewater only)
- Greywater septic tank (sullage wastewater only)
- Effluent may be disposed of via trenches only
- Dry vault system (toilet waste only – waterless)
- Wet system (all household wastewater – may be considered a domestic sewage treatment plant)
- Off the premises by collection from a holding tank by a council-approved liquid waste carrier
- Greywater treatment/diversion facility.
Although council approves the installation of an on-site sewerage facility, the treatment system will require product approval from a State Government Department.
The site and soil evaluator
One of the important aspects of the Queensland Plumbing and Wastewater Code is the requirement for a thorough site and soil evaluation to be undertaken as part of the process of obtaining Council approval for effluent disposal within the property. It is essential for the evaluator to select the most suitable on-site effluent disposal facility for the property and engage the best environmental practices to support his or her design. The quality of effluent from an on-site sewerage facility is a key consideration to determine how sewage effluent is to be controlled and disposed of within the property.
Before lodging an application to install an on-site sewerage facility with Council, it is recommended that the property owner consults with a site and soil evaluator to discuss the options available for effluent disposal within the property.
It is emphasised that maintenance is essential for the satisfactory performance of these facilities.
Aerated wastewater treatment system inspection requirements
A permit to install an aerated wastewater treatment system shall only be granted on the condition that the householder has the installation inspected as per the model approval requirements by a Servicing Agent. A report shall be prepared after each inspection with a copy to be retained by the householder and another to be forwarded to the Council.
The Servicing Agent must be engaged to carry out any necessary repair work to the installation as well as the routine cleaning and maintenance activities.
Any installation faults revealed in an inspection must be repaired promptly.
Council assessment requirements
Council undertakes assessment for on-site sewerage facilities under the requirement of the Plumbing and Drainage Act 2002, the Queensland Plumbing and Wastewater Code and Council's development permit conditions.
The Queensland Plumbing and Wastewater Code sets out the technical requirements for sustainable management, site and soil evaluation, design, installation and operation for on-site sewerage facilities.
This code is to be read in conjunction with AS/NZS 1547 2000, which includes information relating to on-site domestic wastewater management.