Managing the Hidden Risks of Abandoned Underground Tanks

In the world of fuel infrastructure management, the risks you can’t see are often the most dangerous. Buried beneath countless commercial and industrial sites across Australia are underground storage tanks (USTs) that have long been forgotten—or worse, improperly abandoned. These abandoned underground tanks, once used to store flammable liquids like petrol, diesel, solvents or LP gas, may no longer be in service but continue to pose serious hazards.

Flowco Australia is committed to helping businesses identify, manage and mitigate these risks to protect people, property and the environment. This article explores the legal and safety implications of abandoned tanks, the correct process for decommissioning, and why proactive management is critical to compliance and risk reduction.

What Is an Abandoned Underground Tank?

According to WorkSafe Queensland, an underground tank is considered abandoned if it has not been used for two years or is clearly not intended to be used again. This includes tanks that are:

• Fully underground
• Partially buried
• Mounded above ground
• Individual compartments in a multi-compartment system

It’s important to note that a tank does not become “safe” simply because it’s no longer in use. Without proper decommissioning, it remains a significant hazard—retaining flammable vapours, residual sludge or tar, and posing risks of ignition, explosion, and environmental contamination.

A Dangerous Legacy

The dangers posed by abandoned underground tanks are not hypothetical. Historical incidents—some involving tanks that had been forgotten for decades—have resulted in fires, explosions, toxic exposure, significant property damage, and loss of life. Often, these tanks are discovered during construction or excavation work, where the absence of proper records or site plans leads to hazardous encounters.

Even tanks that appear empty can contain highly flammable vapours or residues that ignite with minimal energy input. Routine excavation, welding, grinding or drilling can be enough to trigger a catastrophic event. Many of these tanks remain on properties long after businesses have changed hands, with new owners unaware of their existence until it’s too late.

Legal Responsibilities Under Queensland Law

If you are the person conducting a business or undertaking (PCBU) in control of a site with an abandoned underground tanks, you have a legal obligation to act. Under the Work Health and Safety Regulation 2011 (QLD), regulation 367 requires the PCBU to:

• Identify any abandoned tanks on the premises
• Notify Workplace Health and Safety Queensland (WHSQ) of the abandonment as soon as practicable
• Mitigate risks associated with the tank through removal or decommissioning

Failure to notify WHSQ can result in financial penalties (up to 60 penalty units). Notification must be made using the S367 eForm available via the WHSQ website.

This duty applies regardless of whether you were the operator when the tank was installed. The current controller of the tank bears the responsibility—making it essential for landowners, developers, and facility managers to proactively investigate historical tank installations.

Removal vs In-Situ Decommissioning

There are two main pathways for dealing with abandoned underground tanks: complete removal or safe in-situ decommissioning. Both must follow strict procedures and be carried out by competent professionals.

1. Tank Removal

Where feasible, the tank should be removed entirely in accordance with Australian Standard AS 4976 (The removal and disposal of underground petroleum storage tanks) or AS 1596 for LP gas tanks.

The process of addressing abandoned underground tanks typically involves:

• Draining and cleaning the tank
• Gas-free certification by a licensed professional
• Safe excavation and removal
• Transport and disposal of the tank
• Site backfill and compaction
• Certification of completion and site safety

This is the preferred option as it eliminates all long-term risk. However, in some cases—particularly on developed or congested sites—tank removal may not be practical.

2. In-Situ Decommissioning

If physical removal is not reasonably practicable, the tank must be decommissioned in place. This process includes:

• Cleaning and purging the tank to eliminate flammable vapours (e.g. with nitrogen or carbon dioxide)
• Filling the tank with inert material (such as slurry, foam, sand or concrete)
• Venting and sealing the tank to ensure no further ingress or build-up of gases
• Providing detailed documentation including:
  • A description of decommissioning steps taken
  • Certification from a competent person
  • A diagram showing the exact location of the tank relative to a permanent landmark

The PCBU must also document why removal was not feasible and explain how in-situ decommissioning has effectively eliminated or minimised risk. This documentation must align with Section 366 of the WHS Regulation and the Managing risks of hazardous chemicals in the workplace Code of Practice 2021.

Risk Management: A Proactive Approach

One of the key failings in historical fuel infrastructure management has been the lack of proper handover documentation and risk planning. Flowco advocates for a proactive approach that includes:

• Historical site assessment: Investigate property records, previous uses and fuel supply history
• Site inspection and ground penetrating radar (GPR): Use advanced detection methods to locate undocumented tanks
• Environmental sampling: Check for signs of fuel leakage or contaminated soil around suspected tank areas
• Early engagement: Involve qualified fuel infrastructure experts and engineers as soon as abandoned tanks are suspected

Any delays in addressing abandoned tanks can expose businesses to severe risk—not only legal but also reputational. Landowners looking to redevelop or sell a site must consider these liabilities carefully.

The Flowco Advantage

As a national leader in underground fuel infrastructure management, Flowco brings the technical expertise, regulatory knowledge and on-the-ground experience to help our clients identify and safely manage abandoned underground tanks. We provide:

• Detailed tank location and assessment services
• Risk and compliance audits
• Decommissioning and removal project management
• Liaison with regulatory bodies and submission of required notifications
• Full documentation, site mapping and certification

Flowco works in full alignment with Australian standards, WorkSafe QLD guidance, and EPA expectations. Our team of licensed professionals ensures all abandoned underground tank or decommissioning work is undertaken safely, compliantly, and with minimal disruption to site operations.

A Safer Future Starts Underground

Abandoned underground tanks are an invisible risk—but one that can have devastating consequences if left unmanaged. Whether you’re a fuel retailer, property developer, facilities manager or commercial landowner, knowing what’s buried beneath your site is not just best practice—it’s your legal duty.

Flowco Australia stands ready to support clients through every stage of tank identification, assessment and decommissioning of abandoned underground tanks. By taking action early and engaging the right expertise, you can prevent serious hazards, reduce liability, and maintain the highest standards of fuel system integrity.

The Queensland government has recently review its WorkSafe guidance which can be found here Abandoned underground tanks.

ACAPMA also provides and excellent overview here.

Contact Flowco today to arrange a site assessment or compliance consultation.