Septic System Decommissioning in Ontario: Certificate, Process and What Happens to the Old Tank
Connecting to Municipal Sewer or Tearing Down a Building? Here Is What Happens to the Old Septic System.
When a septic system goes out of service — because the property connects to municipal sewer, because the building is being demolished, or because a replacement system is being installed in a different location — the old system cannot simply be left in the ground and forgotten. Ontario requires a formal decommissioning process and a Decommissioning Certificate from the principal authority. Here is what that means in practice.
Most homeowners encounter septic decommissioning in one of three situations: a municipal sewer extension finally reaches their street and they are connecting, they are demolishing an older building that had a septic system, or they are replacing a failing system whose tank and bed are being abandoned in place while a new system goes in elsewhere on the lot. In all three cases, the abandoned components need to be dealt with properly and documented officially.
What the Decommissioning Certificate Is
A Decommissioning Certificate is the official document issued by your local principal authority — your health unit, Conservation Authority, or municipal building department depending on who administers Part 8 in your area — confirming that a septic system has been properly taken out of service. It closes the file on the original septic permit and records what was done with the components.
Under the Ontario Building Code, a Decommissioning Certificate is required when:
- A building connected to a private septic system is being demolished
- A property is connecting to a newly available municipal sewer system
- A septic system is being replaced and the old tank will be abandoned in place rather than removed
- A property is being severed and the original system will no longer serve the property as configured
In most jurisdictions, the decommissioning application must be submitted and approved before the demolition permit is issued or before the sewer connection can be finalized. Getting the sequencing right matters — confirm with your local authority what they require and in what order before you book contractors.
Who Issues It in Your Area
Part 8 enforcement is handled differently across Ontario. In Niagara Region, it is Niagara Region Public Health. In Simcoe County, depending on the specific municipality, it may be the municipality or the NVCA. In Renfrew, it is the Renfrew County and District Health Unit. In much of Haliburton and Parry Sound, it is the local Conservation Authority. Check our Ontario health unit and CA directory to find your principal authority if you are not sure.
Why You Cannot Just Leave the Old Tank in the Ground
The most common question from homeowners is whether they can simply disconnect the inlet pipe and walk away from the old tank. The answer is no — and the reasons are both regulatory and practical.
Abandoned septic tanks pose genuine hazards. A tank left in the ground with its contents intact will eventually deteriorate. Concrete tanks can crack and collapse. Steel tanks — common on properties with systems installed before the 1980s — rust through surprisingly quickly and become structurally compromised within a few years of being taken out of service. A tank whose lid or walls collapse can create a dangerous sinkhole. Someone — a child playing in the yard, a contractor excavating nearby, a property buyer who does not know the old tank is there — can fall in. Beyond the physical collapse risk, an improperly abandoned tank can release hydrogen sulphide and methane gas from decomposing contents as it deteriorates.
There is also a groundwater concern. An old tank left full of septage that slowly seeps through corroding walls contaminates the soil and potentially the water table around it over time. This is particularly a concern on properties with private wells, near water bodies, or in source water protection zones.
The Old Steel Tank Problem
Properties built before approximately 1980 very often have steel septic tanks rather than concrete. Steel tanks in the ground corrode from both the inside (from hydrogen sulphide produced by the septage) and the outside (from soil moisture and acidic soils). A steel tank that was installed in 1965 may still be holding its shape — or it may be essentially a thin shell of corroded metal that will collapse the moment any weight passes over it. If you are buying a property with a pre-1980 system or planning any work near an old system, locate the tank first and assess its condition. A tank probe or camera inspection by a septic professional can determine whether the tank is still structurally sound before anyone drives equipment over the area.
The Decommissioning Process: Step by Step
The specific requirements vary somewhat by jurisdiction — confirm with your local principal authority before beginning. The following sequence reflects standard Ontario practice:
1
Apply for the Decommissioning Certificate
Submit a decommissioning application to your principal authority before work begins. The application typically requires a site plan showing the location of all tanks and the leaching bed, the original septic permit number if available, and confirmation of what will be done with each component. Most authorities charge a modest fee for the decommissioning application — typically $100 to $300. In many jurisdictions the decommissioning application must be approved before the demolition permit or sewer connection application can proceed.
2
Cap the inlet pipe at the house
Before the tank is pumped, a licensed plumber should permanently cap the sewer pipe that runs from the house to the septic tank. If the property is connecting to municipal sewer, this step happens as part of the sewer connection work — the old connection is capped and the new connection to the municipal lateral is made. The cap prevents any further sewage from entering the old system.
3
Pump all tanks via a licensed hauler
A licensed septage hauler must pump all contents from every tank in the system — the main septic tank, any pump tanks or dosing tanks, and any distribution boxes. The pumping receipt from the licensed hauler is typically required as part of the decommissioning documentation. Never enter a septic tank to check it — the gases produced by decomposing septage (hydrogen sulphide, methane) are immediately lethal in confined spaces. This is strictly a job for licensed professionals with proper equipment.
4
Disconnect electrical components (ATU systems)
If the system includes a pump tank with an effluent pump or an ATU with an air pump or electrical components, a licensed electrician must disconnect and properly secure all electrical wiring before the tanks are filled. Energized electrical components in a tank being filled with soil or concrete are a serious hazard. Do not skip this step on any system with electrical components.
5
Remove or fill the tank in place
Once pumped and empty, each tank must be either removed from the property entirely (the cleanest option but requires excavation and disposal) or filled in place. Filling in place is the more common approach because it avoids the cost and disruption of excavating and removing a large concrete tank. The standard fill-in-place method: collapse the lids into the tank body (for concrete tanks, this is done carefully to avoid a sudden collapse), then fill the void with compacted clean sand, gravel, or concrete. The fill must be compacted to prevent future settling and subsidence at the surface.
6
Address the leaching bed
The leaching bed components — distribution pipes, gravel, sand — can typically be left in the ground if there are no plans to use the area for other purposes and the surface drainage is adequate. If the area will be used for a pool, addition, driveway, or other purpose that involves excavation or loading, the leaching bed material needs to be excavated and disposed of properly at a licensed facility. The health unit may specify what needs to be done with the bed area as part of the decommissioning conditions.
7
Grade and restore the surface
Properly grade the area over any filled tanks to ensure positive drainage away from the former tank location. Establish vegetative cover over any disturbed areas. If surface effluent had been present before the system was taken out of service, cover those areas with hydrated lime followed by topsoil before establishing vegetation.
8
Obtain the Decommissioning Certificate
Submit the completed decommissioning documentation to the principal authority — the pumping receipt, the licensed contractor’s confirmation of the fill work, and any other documentation required. The authority reviews the submission and issues the Decommissioning Certificate, formally closing the septic permit file. Keep this certificate permanently. It is a property record that will matter at future sale transactions.
Connecting to Municipal Sewer: Specific Considerations
When a rural or suburban property connects to a newly extended municipal sewer, the old septic system must be decommissioned as described above. In many Ontario municipalities, connection to available municipal sewer is mandatory within a specified period once the sewer becomes available within a certain distance of the property — often within 200 feet or within the same street block. The municipality’s sewer connection bylaw specifies the timeline and requirements. Do not assume you can simply leave the old system in service indefinitely because it is still functioning.
The sequencing for a sewer connection decommissioning:
- Apply to the municipality for sewer connection approval and note that you will also be decommissioning the private system
- Apply for the Decommissioning Certificate from the principal Part 8 authority concurrently
- Have a licensed plumber make the sewer connection and permanently cap the old sewer line to the tank
- Once the sewer connection is confirmed active, proceed with tank pumping and fill
- Obtain Decommissioning Certificate
The Timeline Gap Problem
One common issue: between the time the municipal sewer is connected and the time the old tank is pumped and filled, the old system is out of service and filled with septage that is no longer receiving fresh wastewater. As the contents age in the tank without the natural biological activity of regular use, they begin to decompose differently and can produce more gas. Do not let an empty-but-unpumped tank sit for weeks or months — complete the pump-out promptly after the sewer connection is made.
What About the Old System When Replacing with a New One?
When a failing septic system is being replaced and the new system goes in a different location on the lot, the old tank is typically abandoned in place (pumped and filled) while the new system is built. In some cases, if the old tank is in good condition and appropriately sized, it can be retained and incorporated into the new system design — converted from the primary tank to a dosing tank, for example. This requires designer assessment and health unit approval but can reduce overall project cost in some situations.
If the old tank is a failed steel tank that is structurally compromised, it should be excavated and removed rather than filled in place — a rusted shell that has already partially collapsed is not a reliable candidate for fill-in-place abandonment. The excavation is messy and adds cost, but it eliminates the collapse and subsidence risk permanently.
The Property Sale Angle
An improperly decommissioned or undisclosed abandoned septic system is a material defect in an Ontario real estate transaction. If a property was connected to municipal sewer at some point but the old septic tank was never properly decommissioned and the seller did not disclose it, the buyer inherits the liability for a potentially dangerous abandoned tank.
In some Ontario municipalities, the presence of an old unpumped abandoned tank is sufficient grounds for the municipality to order remediation at the property owner’s expense. And if an abandoned tank collapses and injures someone, the property owner’s liability exposure is real.
Before listing a property that has ever had a private septic system, confirm that the system was properly decommissioned if it is no longer in service — or disclose its presence and condition accurately if it was not. The decommissioning certificate, if it exists, should be assembled with the other property records and provided to the buyer’s solicitor.
How much does septic decommissioning cost in Ontario?
The cost depends on what needs to be done with the tank. Pumping alone: $400 to $600 for a standard residential tank. Fill-in-place after pumping (crushing and filling a concrete tank with clean sand or gravel): $500 to $1,500 depending on access and the volume of fill required. Full tank excavation and removal: $2,000 to $5,000+ depending on tank size, depth, and site access. The decommissioning application fee to the principal authority: $100 to $300 in most jurisdictions. The total for a standard pump-and-fill decommissioning on an accessible lot is typically $1,000 to $2,500.
Can I decommission my old septic system myself?
The pumping must be done by a licensed septage hauler — this is not a DIY task and is regulated under Ontario law. The physical fill work (once the tank is empty) may be done by a licensed contractor rather than the homeowner in most jurisdictions, depending on local requirements. However, the decommissioning application, the licensed electrician (for electrical disconnection), and the pumping receipt are all components that involve licensed professionals regardless of who does the physical fill work. Confirm with your principal authority what their specific requirements are for your jurisdiction before assuming any portion can be self-performed.
We bought a house and found an old abandoned tank in the yard that was never decommissioned. What do we do?
Contact your local principal authority — health unit or Conservation Authority — and explain the situation. They will advise you on the decommissioning requirements for your jurisdiction. In most cases, they will want the tank properly pumped and filled with documentation submitted retroactively. If the tank is still intact and accessible, the standard process applies — pump, fill, document, and get the decommissioning certificate. If the seller did not disclose a known abandoned tank that they were aware of, this may be a matter to raise with your real estate lawyer.
Do I need to decommission the leaching bed pipes and gravel, or just the tank?
The leaching bed components (pipes, gravel, and sand) can generally be left in the ground if no other use is planned for that area. They are not a collapse or gas hazard the way a void tank is. If you plan to build over, excavate into, or substantially alter the area of the old leaching bed, you should excavate and dispose of the materials at a licensed facility. Confirm with your principal authority what their requirements are — some jurisdictions specify that the bed must be partially or fully removed as part of the decommissioning conditions.
Septic Decommissioning — Key Facts for Ontario Property Owners
- A Decommissioning Certificate from the principal authority is required to formally close a septic permit
- Required when demolishing a building, connecting to municipal sewer, or abandoning an old system
- Application typically must be submitted before demolition permit or sewer connection can proceed
- Pumping must be done by a licensed septage hauler — not DIY
- Empty tanks must be filled with compacted clean sand, gravel, or concrete — not left as voids
- Old steel tanks are at risk of collapse and should be assessed before any work nearby
- Electrical components (ATU, pump tanks) require licensed electrician disconnection before fill
- Leaching bed pipes and gravel can typically remain in place if not being disturbed
- Keep the Decommissioning Certificate permanently — it is a property record that matters at sale
- An undisclosed abandoned tank is a material defect in a real estate transaction
Decommissioning is the unglamorous end of the septic system lifecycle — not the part anyone thinks much about until they need to do it. The process is straightforward when it is handled in the right sequence with the right contractors and documented properly. The problems happen when it is skipped, delayed, or assumed to be someone else’s problem to sort out. It is the current property owner’s problem. A properly decommissioned system, with a certificate on file, is one fewer thing for a future buyer’s lawyer to ask about.
Connecting to Sewer or Replacing a System?
We can help you understand the decommissioning requirements in your area and connect you with a licensed professional to handle the process correctly the first time.