Septic Tank Installation in NSW: The Process From Soil Test to Approval to Operate

A septic tank installation in NSW runs in a fixed order: a site and soil evaluation, a system design, a Section 68 application to council, an approval to install, installation by a licensed plumber and drainer, council inspections before anything is backfilled, and finally an approval to operate. You can’t legally use the new system until council has inspected it and issued that approval in writing.

The digging is the short part. Most of the time goes into the assessment, the design and the application. Here’s each step for a Hunter Valley property, what you do as the owner, and who does the rest.

The process at a glance

The sequence is the same for a new house on vacant acreage or a replacement for a failed system. A new build adds a development application or complying development certificate alongside it.

Start by checking what you actually need

First, is sewer available? The Office of Local Government (OLG) assessment checklist asks council officers whether a sewer connection is available within 75 metres of the site and whether it’s viable. If your block is near a sewered area, ask council early.

Second, if you already have a system, does it really need replacing? The OLG guidelines say an existing system doesn’t have to meet newer standards as long as it meets the performance standards in the Regulation and the conditions of its approval. An old concrete tank isn’t illegal because it’s old. A baffle or pipe repair runs $250 to $650, so we diagnose before anyone quotes a replacement.

For a new dwelling, the OLG’s model approval conditions tie the approval to install to the development consent or complying development certificate, so if the house plans change, the wastewater approval has to be amended before the system goes in. Adding a second dwelling to a block with an existing system is covered in granny flat septic requirements in NSW.

The site and soil evaluation

Everything after this depends on it. The evaluation tells the designer and council what the ground can absorb, where the system can go and what the constraints are.

The OLG guidelines put the responsibility for engaging the assessor on the landowner or developer. They describe someone with a tertiary qualification in a field such as soil science, environmental science or environmental engineering, practical on-site wastewater experience, and current professional indemnity insurance, which the guidelines tell landowners to confirm before engaging them.

The assessor bores test holes, logs the soil profile, and looks at slope, drainage, flooding, depth to groundwater or rock, and distances to bores, dams, waterways and boundaries. On Hunter blocks, heavy clay subsoils, a high water table on river flats and flood-liable land often push the design toward secondary treatment and a larger effluent area. Deeper, better-draining soils keep a conventional tank and trenches on the table.

What you do: engage the assessor (or have us arrange one), give them access to the whole block, and mention any future shed, pool or second dwelling so the system isn’t designed into the way of it.

Designing and sizing the system

Size starts with how many people the house could hold, not how many live there now. The OLG guidelines suggest a conservative design occupancy of 3 people for the first bedroom and 1 for each bedroom after that, unless council sets its own method, and say any room with a door and a window can count as a potential bedroom, including studies, media rooms and home gyms. Our septic tank size calculator gives a first estimate.

Daily flow is then worked out per person: the guidelines’ allowance for a household with standard fixtures is 150 litres per person per day on reticulated or bore water and 120 litres on tank water.

The system has to be an accredited model. Under section 41 of the Local Government (General) Regulation 2021, a council can’t approve installing a domestic septic tank or treatment system of a kind generally sold by retail unless it’s built to a design that holds a current NSW Health certificate of accreditation. NSW Health publishes its register of accredited AWTS models with each certificate’s expiry date, so check the model you’re quoted is on it.

The big choice is usually a conventional tank with absorption trenches or an aerated wastewater treatment system with irrigation, and the soil report often makes it for you. We compare the two in septic tank vs AWTS.

The Section 68 application and approval to install

Section 68 of the Local Government Act 1993 needs two approvals: Part C item 5 to install, construct or alter a waste treatment device such as a septic tank, and Part C item 6 to operate a system of sewage management. The approval to operate isn’t issued until the work has passed inspection.

The owner is the applicant. Many councils take these applications through the NSW Planning Portal. Cessnock City Council takes on-site sewage applications that way, and asks for a declaration and owner’s consent form, the documents on its checklist, and a site and soil assessment report where one applies. Other Hunter councils use their own forms. A typical package includes:

• the site and soil evaluation report
• a scaled site plan showing the tank, effluent area, buildings and distances to water and boundaries
• the house floor plan, so council can check the bedroom count
• the system specifications and its NSW Health accreditation certificate
• the council’s forms, owner’s consent and fee

The OLG guidelines say the council officer will then ask for more information, reject the application, or approve it with conditions. None of the Hunter council pages we checked publishes a processing time, so we won’t guess one; a complete application with a proper soil report avoids extra rounds. The septic fees each Hunter council publishes are compared in our guide to council OSSM rules in NSW.

What you do: lodge the application, sign the consent, pay the fee, and give your contractor a copy of the approval and its conditions. The OLG’s model conditions make passing those conditions on the applicant’s responsibility.

Installation and the inspections before backfill

Nothing gets dug until the approval to install is issued.

The OLG guidelines say all plumbing and drainage leading to the treatment system must be installed by a licensed plumber or drainer, and the treatment system and effluent area by a licensed plumber or drainer or experienced installer, to the approved design. Electrical work is done by a licensed electrician. On jobs we coordinate, installation is carried out by licensed plumbing and drainage contractors we work with; their NSW licence number appears on every quote.

The OLG’s installation guidance describes good practice:

• the hole cleared of roots and rock, with a level bed of 50 mm of compacted sand under the tank
• the tank lowered in, not dropped, using the manufacturer’s lifting points
• lids at least 100 mm above final ground level unless the tank is designed for sealed risers
• joints and lids sealed against stormwater
• in wet ground, water drained from around the tank or the tank anchored against uplift, per the manufacturer and AS/NZS 1546.1

That last point matters on low-lying Hunter blocks and in clay that holds water, where an empty tank can be pushed up out of the ground.

Inspections happen while the work is open. The OLG’s model conditions name the sewer drainage and effluent disposal area as work council must inspect before trenches are backfilled, generally with 48 hours’ notice. Cessnock tells applicants that you or your installer must book these inspections with council directly, at the stages set out in the approval.

On the plumbing side, NSW Government guidance for regional areas (it excludes the Sydney, Illawarra, Blue Mountains and Newcastle areas, so ask your plumber which regulator covers your address) says the plumber or drainer lodges a Notice of Work with the plumbing regulator before starting, books drainage inspections before the work is covered, and on completion lodges a Certificate of Compliance and a sewer service diagram, with copies to you. Keep them with your septic records.

Commissioning, final inspection and approval to operate

For an AWTS, NSW Health’s accreditation conditions say councils should require the manufacturer or its agent to inspect the system and certify it was installed and commissioned to its design, the accreditation conditions and council’s requirements. The owner must also hold a service contract of at least 12 months with a service agent.

The OLG guidelines say installers give the owner and council a commissioning or installation certificate and an “as built” plan. Council’s final inspection is best done with the system running on clean water, so the officer can see every part working and effluent spreading evenly.

Council then issues the approval to operate, with conditions and an expiry date; until then, the system must not be used. For a new house, the approval may depend on the occupancy certificate.

If you’re replacing a system, the model conditions call for the old one to be decommissioned under NSW Health Advisory Note 3, covered in decommissioning a septic tank in NSW. The old tank is pumped out first; the waste is transported and disposed of under NSW EPA waste rules at a licensed treatment facility, and a disposal docket is provided for every load.

What it costs, and where we fit in

Council fees and the assessor’s report are separate, so ask any quote to say whether they’re included. Every replacement or AWTS installation starts with a thorough site and soil assessment and ends with a fixed written quote. The price changes only if scope changes with prior owner agreement.

Our part is diagnosis, arranging the site and soil assessment, sizing the system, Section 68 paperwork support and coordinating the job through to approval. Excavation, setting the tank, trench construction and pipework are carried out by licensed plumbing and drainage contractors we work with; their NSW licence number appears on every quote.

If you’re planning a new system, see our septic system replacement page or call 0468 278 123. We call back within 24 hours during business hours.

Frequently Asked Questions

Do I need council approval to install a septic tank in NSW?

Yes. Section 68 of the Local Government Act 1993 requires council approval to install, construct or alter a septic tank, and a separate approval to operate it. The system can’t be used until council confirms in writing that it was installed in line with the approval.

Can I install a septic tank myself in NSW?

No. The OLG guidelines say plumbing and drainage leading to the treatment system must be installed by a licensed plumber or drainer, and the system itself by a licensed plumber or drainer or experienced installer. Electrical work for an AWTS must be done by a licensed electrician.

Who does the site and soil assessment?

The landowner engages a suitably qualified and experienced assessor. The OLG guidelines describe someone with a tertiary qualification in a field such as soil science or environmental engineering, on-site wastewater experience and professional indemnity insurance. Ask your council if it has its own requirements.

How long does septic approval take in the Hunter?

None of the Hunter council pages we checked publishes a processing time. Cessnock checks an application and requests missing information before formally lodging it, so a complete package with a proper soil report is the best way to avoid delays.

What inspections happen during a septic installation?

Council inspects at the stages listed in your approval to install, usually including the drainage and effluent area before backfilling, and a final inspection with the system running. The plumbing regulator may also inspect the drainage before it’s covered.

When can I start using a new septic system?

Only once council has issued the approval to operate after a satisfactory final inspection. For an AWTS, the manufacturer or its agent must also commission and certify the unit, and you need a service contract in place.

Sources and further reading

• NSW Office of Local Government, Onsite Wastewater Management Guidelines (April 2025): Section 68 approvals, the sewer check, site and soil assessors, design occupancy and flows, installation practice, inspections and model approval conditions.
• NSW Ministry of Health, Secondary Treatment System Accreditation Guideline: accredited systems only, commissioning by the manufacturer or agent, the 12-month service contract.
• NSW Health, Aerated wastewater treatment systems register: accredited AWTS models and certificate expiry dates.
• NSW Planning Portal, Section 68 approvals: approvals to install and operate, online lodgement.
• Cessnock City Council, Understanding our application process: Portal lodgement, documents, staged inspections, approval to operate.
• NSW Government, Regional plumbing and drainage inspections: Notice of Work, inspections before backfill, Certificate of Compliance and sewer service diagram (regional NSW outside the Sydney, Illawarra, Blue Mountains and Newcastle areas).