Septic tank or aerated wastewater treatment system: which suits your block?

A conventional septic tank settles and digests sewage without power and sends the liquid into absorption trenches in the soil. An aerated wastewater treatment system (AWTS) adds air and a second treatment stage, so the effluent is cleaner and can go to garden irrigation, but it needs electricity and a service every three months. Which one suits a rural block near Sale depends mostly on the soil, the space available and what the council permit allows for that site.

How do the two systems compare?

Point	Conventional septic tank	Aerated wastewater treatment system
Treatment level (EPA Victoria)	Primary: settling and anaerobic digestion, no set effluent standard	Secondary: aerobic treatment after settling, to a set effluent standard
Where the effluent goes	Absorption trenches or beds below ground	Usually subsurface irrigation; surface spray needs disinfection as well
Power	None for a gravity system	Needs a continuous supply for the blower and pumps
Routine servicing	Inspect and desludge at least every three to five years	Service agent every three months, plus desludging
Soil it suits	Not recommended in sandy soils or heavy clays without special design	Better suited to constrained or sensitive sites
Land needed	Trench area plus a reserve area of the same size	Irrigation area sized to the soil and household
Consumables	Few	Possibly chlorine or other disinfection, and replacement parts
Permit	Wellington Shire permit to install or alter	Same permit path

The treatment and dispersal rows draw on the EPA Guidelines for onsite wastewater management, publication 5001. The servicing row follows Wellington Shire Council’s reminder to owners of onsite systems.

What does each system actually do to the wastewater?

Septic tank. Everything from the toilet, kitchen, bathroom and laundry runs into a sealed tank. Solids sink to form sludge, fats float as scum, and bacteria that need no oxygen break some of it down. The liquid in the middle flows out to trenches, where the soil does the rest of the treatment. EPA Victoria calls this primary treatment and sets no quality standard for it. It recommends that every treatment plant has an outlet filter to hold back solids and grease.

Aerated system. The first chamber does the same settling job. Then air is pumped through a second chamber so oxygen-loving bacteria can break down far more of the waste, followed by settling or filtering. EPA Victoria classes this as secondary treatment, with limits on biochemical oxygen demand and suspended solids that the effluent has to meet. Some approved units add disinfection or nutrient reduction, which matters near waterways and in water supply catchments.

Which one does your soil and block favour?

Soil type is often the deciding factor, and it is why the council may ask for a land capability assessment (LCA) before approving anything.

• Sandy soils. EPA guidance says absorption trenches are not recommended in sands because water moves through too fast and can carry pathogens and nutrients to groundwater. Primary-treated effluent should not be dispersed in sands or gravels where groundwater is at risk. That pushes sandy sites toward secondary treatment.
• Heavy clays. Trenches are also not recommended in heavy clay because the soil takes water too slowly. A designed system or an irrigation layout spread over a larger area is usually needed.
• Loams and lighter clays. Conventional trenches often work, laid level, on the contour, with set spacing between runs.
• Small or tight blocks. Wellington Shire lists blocks under 8,000 square metres, closeness to waterways, shallow groundwater and poor soil among the constraints that can trigger an LCA.

A septic trench layout also needs a reserve area kept free for a second set of trenches if the first ones fail. On a smaller block that spare land can be the reason an aerated system with drip irrigation is chosen instead.

What do the running costs and upkeep look like?

This site does not quote an installed price for a new system, because soil, block size, the LCA findings and the unit chosen move the total too far for a guide figure to help. Ongoing costs are easier to compare.

• A service visit for either type is in the range of $290 to $660 per visit, according to the 2026 Gippsland guide used on the plumbing costs page for Sale.
• An aerated system has four of those visits a year, every three months, as Wellington Shire requires in line with the maker’s instructions.
• Both types need desludging at least once every three to five years, depending on how heavily the house uses the system and its type.
• The aerated system adds an electricity bill for the blower and pumps, and possibly disinfection tablets and replacement parts.

For a house that sits empty for weeks, EPA guidance notes that a powered treatment plant may need a low-flow switch that recirculates effluent while nobody is home. Raise it early if the property is a weekender.

What do you have to do as the owner, whichever you choose?

Wellington Shire reminds owners that under the Environment Protection Act 2017 and the Environment Protection Regulations 2021 they must:

• keep the system in good working order and stop it overflowing
• have an aerated plant serviced by a service agent every three months
• desludge at the three to five year interval
• tell the council about any problem and what is being done to fix it
• give tenants written information on how to run and look after the system
• keep pump-out and service records for five years and show them if asked.

The council’s onsite wastewater page lists warning signs such as wet or pooling ground over the absorption area, a sewage smell near the system and slow drains or toilets. The septic systems service page covers inspections, faults and decommissioning in more detail.

How does the Wellington Shire permit work for either system?

The steps are the same for both. Wellington Shire issues permits to construct, install or alter systems that handle up to 5,000 litres a day, under the Environment Protection Regulations 2021, and the unit must be one EPA Victoria has approved.

1. Lodge the council’s Application to Install or Alter with a scaled site plan, house floor plans and an LCA if one is required.
2. An Environmental Health Officer inspects the site with the owner and the plumber to settle the most suitable system.
3. The council issues a Permit to Install or Alter. No work starts before it.
4. The plumber installs the tank and dispersal area, at least 2 metres from house foundations and the boundary unless approved otherwise, with effluent going to the low side of a sloping block.
5. A final inspection happens before the tank and trenches or irrigation lines are backfilled.
6. The plumber lodges a compliance certificate with the state regulator, and the council then issues the approval to use.

The installation has to be finished within two years of the permit being issued. The council’s own page still names the Victorian Building Authority for step 6, but plumbing certificates now go to the Building and Plumbing Commission. The compliance certificate guide explains that step. Design of the dispersal area follows AS/NZS 1547, the Australian and New Zealand standard for onsite domestic wastewater management, which EPA guidance cites throughout.

What is the local picture around Sale?

This comparison mostly concerns farm and lifestyle blocks outside the sewered parts of the towns. On dairy and irrigation land around Maffra, or beside the flood-prone Latrobe River near Longford, a block that floods or stays wet is exactly the kind of constraint an LCA is written to deal with. Loch Sport is a different case: Gippsland Water connected it to a pressure sewer network, as it did Coongulla and Glenmaggie, so most homes there have a pump unit on the property rather than a septic tank. If you are not sure whether your address is sewered, Gippsland Water or the council can tell you before you pay for any design.

The plumber who designs and installs the system will be an independent licensed business that prices the work itself, and this site does not choose the system for you. If you are weighing a replacement now, send a septic or treatment system enquiry with what you already know about the block.

Next step

Put these in your enquiry so a provider can tell you which path is realistic: the property address or nearest road, block size, whether you have an existing tank and roughly how old it is, the number of bedrooms, any LCA or council letter you already hold, and photos of the tank lids and the area where effluent goes now. Then ask a licensed plumber about replacing your septic system and it will reply with its own advice and price.

Send a job enquiry