What is an On-site Sewerage Facility?
On-site sewerage facilities (OSSF) consist of wastewater systems situated within property boundaries that treat the sewerage generated from the property and the land application area of the treated effluent. A large number of properties in the Southern Downs are not connected to a reticulated sewerage system. The treatment and disposal of all wastewater generated on these properties must then be undertaken by an on-site sewerage facility.
An on-site sewerage facility is any system that captures, stores, treats and disposes of household wastewater on the property. OSSFs include all types of wastewater treatment and land application, such as septic tanks, aerated wastewater treatment systems, biofilter systems, composting toilets, and activated sludge systems.
The disposal of effluent (treated sewage) may occur:
- on the property on a designated area (called a land application area)
- off the premises by collection from a holding tank by a council-approved liquid waste carrier.
- off the premises by a common effluent drainage system.
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. Such systems over 20 equivalent persons would also require approval and further monitoring from the Department of Environment and Heritage Protection.
Legislation supporting on-site sewer systems
Council undertakes assessment for on-site sewerage facilities under the requirement of the Plumbing and Drainage Act 2018, 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 2012, which includes information relating to on-site domestic wastewater management. For more information refer to Building Codes Queensland On-site sewerage facility requirements (PDF 3.5MB).
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 consult with a site and soil evaluator to discuss the options available for effluent disposal within the property
For more information refer to the Department of Housing and Public Works website.
Information for Owners
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. Maintenance is essential for the satisfactory performance of these facilities. Owners of properly maintained systems benefit from more efficient systems with a longer life, reduced health risk and improved environmental quality.
Commissioning Certificate
Following the installation of a wastewater treatment plant, the manufacturer of the plant is to certify that the facility conforms to design requirements and specifications and that such equipment has been installed and commissioned in accordance with manufacturer’s instructions.
Maintaining Your System
Maintenance requirements differ depending on the type of system you have. State legislation require that aerobic wastewater treatment plants be serviced every three months and aerobic sand filter treatment systems annually. A licensed service agent must be engaged by the property owner to carry out the maintenance and to advise Council of the performance of your system. Service agents will normally conduct the following:
- Maintenance to mechanical equipment
- Check accumulated sludge levels
- Check irrigation system operation
- Add chlorine and check operation of the disinfection system
- Removal of sludge and scum from the clarifier/final chamber
De-sludging Your System
Periodic removal of accumulated sludge and scum from the primary treatment section of your OSSF is required to be carried out by a licensed waste contractor.
Be a Good Neighbour
Effluent must be disposed of within the boundaries of the property from which it was generated. It is an offence to dispose of effluent run-off or spray drift onto adjoining properties.
OSSF Approved Systems
For a list of approved systems go to Queensland Government Department of Housing and Public Works or contact them on 13 74 68.
Caring for Your OSSF
- Carry out regular maintenance of OSSF using an approved servicing agent. It is an offence if your OSSF is not maintained regularly by an approved service agent.
- Use only recommended biodegradable products.
- Avoid contact with the effluent and irrigation sprays.
- Call your service agent when you are encountering problems with your system such as alarms and/or smells from the OSSF.
- Conserve water and avoid overloading the system. Fix leaking taps and running toilets as soon as they are discovered.
- Use toilet paper that disintegrates easily.
- Use bicarb soda as a cleaner for toilets, baths and basins.
- Keep a detailed record about your treatment plant, including model number, service agent, records of service visits, maintenance performed and parts replaced.
- Become familiar with how your own particular system operates and the way it looks sounds and smells when it is working correctly. This way, you may be able to identify problems before they become serious and alert your service agent to anything unusual.
- Ensure your OSSF tank lids are properly sealed to prevent entry of mosquito and other vermin.
- Put food scraps, milk or oil down the sink.
- Dispose of any product containing ammonia, acids, disinfectants or bleaches into the system as it will kill the bacteria which operate the system.
- Allow roof or surface water to enter the system as it will overload the system.
- Allow foreign objects such as plastic or rubber products, cloth, rags, sanitary napkins, bones, metal, glass and tea leaves or coffee grounds to enter the system as they may cause blockages.
- Switch off the system to save power.
- Cover tanks with earth, concrete, pavers, pine bark, mulch or other material which could interfere with access for maintenance or enter the tank when lids are opened.
- Allow anyone to park on, or drive over any part of the system.
- Make or allow unauthorised repairs or alterations to your system without approval from Council.
- Use garbage grinders unless the on-site sewerage facility is designed to cope with this waste.
- Put any chemicals such as paints, thinners, pesticides etc. into the sink as these items can destroy the bacteria digestion process in your system, resulting in the discharge of polluted effluent.
Types of OSSFs
These provide secondary treatment or better, with:
- 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
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.
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 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.