Hidden toxic holes under Aus backyards a ticking time bomb

A legacy coal exploration hole lifting water and methane to the surface. Picture: The University of Queensland

A small hidden hole silently spewing as much toxin as 10,000 cars has sparked fears that thousands of unsuspecting Aussies could be living on top of ticking time bombs.

The shock discovery by the University of Queensland has raised alarm over as many as 130,000 toxic, abandoned exploration boreholes under Aussie homes, farmlands and acreages, some of which may never have been properly sealed with potentially dire consequences for property values, insurance costs and even family health.

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The portable Quantum Gas LiDAR system, towed on a trailer, with the borehole fenced off in the background. Picture: The University of Queensland

To the naked eye the boreholes look like nothing more than bare patches in a paddock or backyard, but could be leaking dangerous gases day and night, undetectable without special equipment.

The level of these emissions is shocking, according to University of Queensland Gas & Energy Transition Research Centre researchers Associate Professor Phil Hayes and Dr Sebastian Hoerning who took emissions readings over a week at a farm in the Surat Basin in central southern Queensland.

Their research, published in the Science of the Total Environment journal, found a single abandoned borehole was leaking 235 tonnes of methane every year – making it a “super-emitter”.

What’s worse is Queensland alone has an estimated 130,000 of these holes, many of them drilled decades ago, with little official record of how safely they were sealed – and in some cases even where they are located.

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Corehole emissions tracking was undertaken by researchers with water boreholes next. Picture: The University of Queensland.

Even if only a small fraction are leaking at the scale of the hole UQ measured with advanced gas detection technology, thousands of properties could be unknowingly affected.

A 2024 Healthy Futures report on the health effects of methane pollution warned leaks contributed to formation of ground-level ozone, “a toxic lung irritant linked to respiratory problems like asthma, chronic obstructive pulmonary disease, and even heart disease”, according to the Australian Nursing and Midwifery Journal.

Dr Hayes said their study was “the first long term measurement of methane emissions from an abandoned coal exploration borehole”.

“This borehole is one of an estimated 130,000 in Queensland where the quality of sealing by coal explorers is unknown.”

Dr Hoerning said there were thousands of abandoned coal holes and it was not known how well they are sealed – if at all – or how much methane they may be emitting.

“While the majority of these boreholes won’t be emitters, our measurements show they could be a major source of greenhouse gas emissions that is currently unreported.”

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The abandoned coal exploration borehole was drilled many years ago in a paddock in rural Queensland. Picture: The University of Queensland.

The researchers took emission readings using a portable Quantum Gas LiDAR system, UQ said, with the equipment providing more accurate emissions readings than common measurement methods such as handheld sensors.

“Our research has revealed a problem, but also an opportunity,” Dr Hayes said. “Sealing the worst offending boreholes represents a straightforward and cost-effective way to quickly reduce greenhouse gas emissions.”

The pair hope to expand their study to even potentially capture emissions from water bores, of which they are significantly more across the country.

Dr Hayes said the issue “may not be limited to coal boreholes, and we would be interested to study the emissions potential of water bores”.

“We hope our work can eventually help reduce overall greenhouse gas emissions across Queensland and beyond.”

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This hole has since been sealed. Picture: The University of Queensland.

For hundreds of thousands of property owners who may have hidden mineral exploration or water boreholes in their backyard unbeknown to them, the issue raises urgent questions including whether they could impact property values, if they’d need to disclose them in contracts of sale, and what impact they could have on insurance and bank costs and coverage.

Exploration licences for drilling boreholes are issued by government departments and landowners are obliged to give mining and exploration companies access to the approved drill sites but via a written agreement between the parties concerned.

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