Care and maintenance of septic systems
Septic systems treat wastewater from household toilets and grey water from the laundry, kitchen and bathroom. This treated water can then be safely dispersed below ground.
Find the septic systems frequently asked questions below.
There are two types of septic systems – all purpose and split systems.
- All-purpose systems collect all household wastewater and treat it in one tank, discharging through a distribution box into a land application area (septic trenches).
- Split systems use two tanks to treat wastewater. Toilet water is discharged into the septic tank then through a distribution box to the land application area (septic trenches). Greywater is discharged to a holding tank before being distributed to the garden. The kitchen sink waste is connected to a grease trap which collects any oils or fats before the wastewater reaches the holding tank.
Bacteria break down the solids in the septic tank. The end products are mainly water and sludge (undigested materials), which sinks to the bottom of the tank, and scum that floats to the top of the tank.
A healthy septic system is a living ecosystem – the bacteria needed to break down solids must be in the right proportion to digest the waste.
This guide provides advice on how to ensure your system is healthy and in top working order.
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The contents of a healthy septic tank should form three layers:
- a layer of fats (scum) which floats to the surface
- a clear layer (settling zone called effluent)
- a layer of solids (sludge or bio-solids) which sinks to the bottom.
The scum helps prevent odours escaping and stops air entering. The treated effluent flows out of the tank through an outlet pipe as new wastewater enters.
Septic tanks do not kill pathogenic bacteria, viruses or parasites. Effluent must be treated with extreme caution and contact with people, food, clothing and pets must be prevented. Make sure you thoroughly wash your hands and anything else that accidentally comes into contact with effluent.
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In most septic systems, effluent is discharged from the septic tank directly into the soil via pipes and trenches. Special absorption fields may need to be constructed in areas where the soil is shallow or unsuitable.
At this stage, the effluent still contains large amounts of dissolved pollutants and contains disease-causing pathogens, for example, viruses, bacteria and worms.
Bacteria break down more of the nutrients that can cause problems with the soil in the septic trenches. This is a slow process – soil bacteria need oxygen to work, so it is important not to disperse too much effluent at one time.
The effluent evaporates over time, and is taken up by nearby plants or leaches into ground. A hazard is created when effluent flows into drainage channels, creeks or rivers.
Split systems have a separate tank for grey water and a grease trap for collecting oil and grease from the sink. The trap is designed to remove any grease so it does not clog the grey water (sullage) tank.
The baffles in the grease trap must be checked and replaced when required. Grease traps should be cleaned and checked approximately every three months.
Commonly, there are two types of baffles – inlet and outlet – which need to be in place to avoid solids overflowing from the septic tank to the septic trenches. Overflow will cause the trenches to fail and is an expensive problem to fix.
Top five tips to prevent your system failing:
- Do not put non-organic materials like plastics down the toilet or sinks.
- Do not put chemicals like solvents, oils, paints, disinfectants, pesticides, household cleaning products and bleaches in sinks and toilets as they can kill the helpful bacteria in your septic system.
- Switch to natural cleaners if possible and use smaller amounts. Particularly avoid cleaners that contain high levels of phosphorous.
- Change to low phosphorous washing powders – this can make a difference to the amount of phosphorus entering waterways from septic systems.
- Use traditional non-toxic cleaners like vinegar or bicarbonate of soda in the kitchen and bathroom.
Please ensure that you:
- do not cover tanks with earth, concrete, pavers or any other material
- maintain easy access to any inspection openings
- do not allow roof or surface water to enter any part of the system
- maintain grass and plants growing over septic trenches.
You are required by law to have your septic system inspected by a licensed person every five years.
You must provide City of Gold Coast with a copy of the inspection report on the form sent out to remind you that your system is due for inspection.
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