On-site Sewage Management

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Details: Written by: Adam Gatt; Published: 06 December 2018; Last Updated: 06 December 2018

Council's role & policy

On-site Sewage Management (OSSM) Systems are regulated by the Local Government Act 1993. All NSW councils must monitor the operation of OSSM systems in their area. This is especially important in Penrith City where there are a large number of rural properties and some un-sewered villages.

You need Council approval for the installation or operation of on-site sewage management systems under section 68 of the Act.

See Council's On-site Sewage Management and Greywater Reuse Policy.

Aerated Wastewater Treatment Systems (AWTS)

An AWTS is used for the treatment and disposal of septic wastewater. It consists of a series of treatment chambers combined with an irrigation system. An AWTS enables people living in areas not connected to sewage to reuse their treated wastewater.

In an AWTS, wastewater is treated in multiple stages through several different chambers, within a 1 or 2 tank system.

All wastewater from the household will enter the first tank. This tank is essentially the septic tank. In this tank, the solids settle to the bottom forming a sludge layer while the fats and greases collect at the surface forming a scum layer. Micro-organisms in this first chamber slowly break down the matter in both the scum and sludge layers. Any material that cannot be broken down will gradually build up, and over time, the tank will need to be pumped out periodically.

The primary treated water will then enter a second chamber. In this tank, oxygen is pumped through the effluent in order to encourage digestion of waste products by aerobic bacteria.

The third chamber allows for clarification to occur through the secondary settling of any remaining solids or suspended material. These solids are then returned to either the first or second chambers for further treatment.

Finally, the effluent will go through a disinfection process generally using either chlorine tablets or ultra-violet light as treatment, before being pumped to an irrigation area. Treated effluent can be disposed via sub-surface irrigation, or low throw spray irrigation in certain cases.

Requirements for AWTS

As outlined above, there are two main methods of effluent disposal from an AWTS:

Disposal via subsurface irrigation: The effluent is pumped into a series of irrigation pipes that discharge via holes in the pipe directly into the ground.
Disposal via surface irrigation: The effluent is irrigated over a disposal area by sprinklers that have a maximum plume height of 40cm. Appropriate signage is required to be erected on the disposal area alerting people that wastewater is being disposed on the area.

The disposal area must be correctly sized to allow effective disposal of treated effluent. Treated effluent must not run onto, or be sprayed on neighbouring properties or other high risk areas. To assist in this, the following guidelines outline the requirements for irrigation areas:

Minimum required buffer distances for OSSM systems

All land application systems

100 metres to permanent surface waters (eg rivers, streams, lakes)
250 metres to domestic groundwater well
40 metres to other waters (eg farm dams, intermittent waterways and drainage channels)

Absorption systems

12 metres if area is up gradient and 6 metres if area down gradient of property boundary
6 metres if area up gradient and 3 metres if area down gradient of swimming pools, driveways and buildings

Surface spray irrigation

6 metres if area up gradient and 3 metres if area down gradient of driveways and property boundaries
15 metres to dwellings
3 metres to paths and walkways
6 metres to swimming pools and recreational areas

Surface drip and trickle irrigation

6 metres if area up gradient
3 metres if area down gradient swimming pools, property boundaries, driveways and buildings

Subsurface irrigation

6 metres if area up gradient a
3 metres if area down gradient swimming pools, property boundaries, driveways and buildings

For more information see Council's On-site Sewage Management and Greywater Reuse Policy

Servicing your AWTS

Most AWTSs need servicing by an approved contractor at a cost to the owner every three months (unless otherwise accreditated by NSW Health). The owner is responsible for organising these service inspections and the servicing needs to be carried out in accordance with the manufacturer's instructions. Generally, your service contractor should check the mechanical and electrical functions of the system.

A service contractor will need to fill out a service report sheet after completing a service. A copy of each service report is to be provided to Council for registration within fourteen days of each service. It is the responsibility of the owner to ensure that Council is provided with the most updated record of the AWTS service sheet. Penrith City Council maintains a register of the servicing of each system in the local government area, and failure to submit the report may result in Council inspecting the AWTS at a further cost to the owner.

AWTS - dos and don'ts

Due to the mechanical components of an AWTS, the NSW Department of Health requires each system to undergo compulsory servicing by an appropriately qualified technician to ensure effective functioning. For the majority of approved systems, this service is conducted quarterly.

The following trouble-shooting tips will help to ensure that your system continues to operate correctly:

What you should do

Contact Council for advice and information if you are planning to install an AWTS on your property.
Ensure that you regularly inspect your septic system.
Have your AWTS inspected and serviced four times a year by an approved contractor (assessment should be applicable to the system design).
Provide a copy of each service sheet to Council within 14 days.
Have your system service include an assessment of sludge and scum levels in all tanks as well as the performance of irrigation in the disposal areas.
Have your tank desludged every 3-5 years, or on advice from the service agent.
Have your disinfection chamber inspected and tested quarterly to ensure correct disinfection levels.
Have your grease trap (if installed) cleaned out every 2-6 months.
Keep a record of pump-outs, inspections, repairs and all other maintenance work.
Conserve water use in the household to reduce water load on the system.
Use biodegradable liquid detergents such as concentrates with low sodium and phosphorus levels.
Ensure grass is maintained on and around the disposal area, and that plants used around the disposal areas are able to tolerate high amounts of water and nutrients. Avoid planting trees within 4 metres of your septic tank. Roots could, in the future, create cracks in the tank sides.
Place signs around the irrigation area clearly indicating that the treated effluent is not to be used as potable water.
Familiarise yourself with the layout and location of your AWTS and wastewater disposal area.

Desludging- The septic tank will need desludging when the scum and sludge levels are too high. An AWTS should be pumped out every 3-5 years. It is important that you do not wait until the system fails before having the tank desludged.

What not to do

Do not put bleaches, disinfectants, whiteners, nappy soakers and spot removers in large quantities into your AWTS via the sink, washing machine or toilet. These products can interfere with the bacterial breakdown in the tank and the treatment of effluent.
Do not allow any foreign materials such as nappies, sanitary napkins, condoms and other hygiene products to enter the system.
Do not use more than the recommended amounts of detergent.
Do not pour fats and oils down the drain.
Do not switch off the power to the AWTS, even if you are going on holidays.
Do not allow animals to graze on the effluent disposal area.
Do not allow children or pets to play on disposal area.
Do not water fruit or vegetables with treated effluent.

Warning signs to look out for

Be aware of warning signals indicating that there may be a problem with your AWTS. It is important to ensure that these problems are attended to immediately to protect your health and the environment.

Water that drains too slowly
Drain pipes that gurgle or make noises
Water backing up into your sink which may indicate that your system is already failing
Wastewater pooling over the land application area
Black coloured effluent in the aerated tank
Poor vegetation growth in the irrigated area
Excess noise from the blower or pumping equipment
Septic odour from the tank or disposal area- this may indicate a serious problem. Odour problems from a vent on the AWTS can be the result of slow or inadequate breakdown of solids. Call a technician to service the system.

If you are experiencing any of these signs, you should contact your service contractor to inspect the system. A poorly maintained AWTS can be a serious source of water pollution and may present health risks, cause odours and attract vermin and insects. By looking after your treatment system you can do your part in helping to protect the environment and the health of you and your family.

Common causes of problems with AWTS

Overuse of water

On-site disposal systems generally do not respond well to large volumes of water entering the system from the house hold. As such, it is important to conserve water.

Stormwater entering the AWTS

Stormwater can sometimes enter the septic tank or pipelines through cracks and increase the volume of water entering the septic tank which may overload the system. If you believe this to be occurring, contact a licensed plumber immediately to rectify the problem.

Detergents and chemicals going into the system

On-site management systems rely on bacteria to digest effluent. Bacteria within on-site treatment systems are unable to break down material from detergents and chemicals, and may actually be killed by them.

Absorption Trench Systems (ATS)

What is an ATS and how does it work?

It’s a type of land application system where wastewater is gravity-fed or pumped from the septic tank to an absorption area. The absorption area consists of a trench, usually constructed below ground. Typically, these trenches consist of a durable self-supporting arch, gravel and sand.

Wastewater from the septic tank is gravity-fed or pumped to sub-surface trenches.

All wastewater from the household will first enter the septic tank. In this tank, the solids settle to the bottom forming a sludge layer while the fats and greases collect at the surface forming a scum layer. Micro-organisms in this tank slowly break down the matter in both the scum and sludge layers. Any material that cannot be broken down will gradually build up, and as a result the tank will need to be pumped out periodically.

The partially treated effluent will then flow, or is pumped, to an absorption trench for disposal. The effluent is distributed along the length of the trench via a system of pipes, and is filtered through the gravel and sand and into the soil.

Eventually, the wastewater is absorbed by the soil and by plant roots around the absorption area. As such, to ensure that the system operates correctly, it is essential that the trench system is not overloaded with large volumes of wastewater from the household.

Requirements for ATS

Absorption trench systems are not recommended in sensitive locations, areas which consist of heavy clay soils or areas of high density development, because of their potential to contaminate the groundwater.

Minimum buffer distances for various ATS

All land application systems

100 metres to permanent surface waters (eg rivers, streams, lakes)
250 metres to domestic groundwater well
40 metres to other waters (eg farm dams, intermittent waterways and drainage channels)

Absorption system

12 metres if area is up gradient and 6 metres if area down gradient of property boundary
6 metres if area up gradient and 3 metres if area down gradient of swimming pools, driveways and buildings

Surface spray irrigation

6 metres if area up gradient and 3 metres if area down gradient of driveways and property boundaries
15 metres to dwellings
3 metres to paths and walkways
6 metres to swimming pools and recreational areas

Surface drip and trickle irrigation

6 metres if area up gradient
3 metres if area down gradient swimming pools, property boundaries, driveways and buildings

Subsurface irrigation

6 metres if area up gradient
3 metres if area down gradient swimming pools, property boundaries, driveways and buildings

Typically trenches will be 300mm to 900mm deep. However the depth and the overall length of the trench is dependant on the soil type and anticipated wastewater value.

ATS - dos and don'ts

Even a well designed and properly operating septic tank and absorption trench system will eventually fail if it is not maintained. Disposal trenches should last for approximately 15-25 years, however if they are not built or maintained to an acceptable standard, the trench life can be reduced to as little as two years. Regular maintenance is essential in prolonging the life of your absorption trench and avoiding costly repairs.

What to do

Contact Council for advice and information if you are planning to install or extend an Absorption Trench System on your property.
Ensure that you regularly inspect your septic system.
Ensure that proper soil tests are done during the designing stage of the system, so as to determine what the dimensions your trench should be. An alternative disposal area should also be identified.
Ensure stormwater is diverted away from the absorption trench. Install stormwater diversion devices or contour mounds upslope of the trench such as an earth bund wall. This will help reduce the load on your trench in wet weather.
Maintain grass cover over the surface of the trench to allow for the uptake of nutrients and water from the soil. This can aid evaporation and breakdown of pathogens and nutrients within the effluent.
Ensure absorption area has full access to sunlight. This can aid evaporation and breakdown of pathogens and toxins within the effluent.
Plant shrubs down-slope and away from the trench system to help absorb effluent. Water loving shallow rooted plants are best.
Minimise the use of detergents, bleaches and disinfectants around the home.
Fence off the trench area.
Have a plumber fit an effluent filter to the septic tank to keep solids in the tank.
Have your grease trap (if installed) cleaned out every 2-6 months.

What not to do

Do not flatten diversion contact mounds.
Do not plant trees or shrubs directly on top of the septic tank or absorption system. Avoid planting trees within 4 metres of your septic tank, as roots could, in the future, create cracks in the tank sides.
Do not build structures on top of the absorption system.
Do not drive or park machinery or vehicles on top of the absorption system.
Do not allow animals to graze on top of the absorption system.
Do not cover trenches with concrete, bricks, pavers etc.
Do not store loads of soil or other materials on your disposal area.
Do not place extra topsoil on top of your trench to 'soak up' overflowing effluent if the trench is failing. If there is water pooling over the trench, it is best to call a licensed plumber and have it checked.
Do not flood the disposal area with sprinklers or hoses.
Do not allow children or pets to play on the absorption area.

Warning signs to look for

You can look out for a few warning signs that signal that there may be problems with your Absorption Trench System. Ensure that these problems are resolved immediately to protect your health and the environment.
Muddy/boggy soil during dry periods, in the area directly over or immediately beside the absorption trench system.
A strong sewage odour detected.
Large amounts of dark green grass and weeds growing around absorption area.
Gurgling sounds in the plumbing.
Backup of sewage in house plumbing.
If you notice any of these signs, contact a licensed plumber immediately.
If you have attempted all suggested trouble-shooting tips and you are still having problems with your system, it may be time to replace it. Contact Council's Environmental Health Officers for information and advice on what type of system will suit your needs.

Common causes of problems with ATS

Overuse of Water- On-site disposal systems generally do not respond well to large volumes of water entering the system from the household. As such, it is important to conserve water.

Stormwater entering System- Stormwater can sometimes enter the septic tank or pipelines through cracks and increase the volume of water entering the septic tank which may then overload the system. If you believe that this is occurring, contact a licensed plumber immediately to rectify the problem.

Detergents and chemicals going into the system-On-site management systems rely on bacteria to digest effluent. Bacteria within on-site treatment systems are unable to break down material from detergents and chemicals, and may actually be killed by them.

Compaction- The soil above an absorption area will compact through the movement of vehicles, pedestrians or animals on the absorption field. Soil compaction has negative effect on the adequate treatment and draining of effluent.

Desludging- The septic tank will need desludging when the scum and sludge levels are too high. An absorption trench system should be inspected periodically and the tank should be pumped out every 3-5 years. It is important that you do not wait until the system begins to fail before having the tank desludged - once a tank has failed, desludging will not necessarily make it work again.

Failure of the trench- Blockages and excess wastewater entering the absorption trench system can cause it to fail. You can often tell that a trench has failed because seepage may be evident, and/or effluent may be pooling on the surface, and/or a septic odour may be detected, and the area will also often be covered with profuse grass growth.