Highbury Landfill Authority managing their contaminated while others lurk beneath homes

The disturbing case of the sinking home in Pasadena could be the tip of the iceberg with old landfill sites littered across Adelaide, but at least Highbury is safe from development.

Hidden dangers may lurk beneath homes all over Adelaide that were built on top of old dumps, says the chairman of the authority managing a contaminated site in the northeast suburbs.

Highbury Landfill Authority chairman John Minney said it was absolutely clear that the disturbing case of a sinking home in Pasadena, reported by the Sunday Mail last week, showed development must be restricted around old dumps, including clay pits and quarries filled with all sorts of rubbish.

“It wasn‘t until the early ’60s when people started to understand that there was a problem with dumping waste of this nature in that manner,” Mr Minney said.

“The dumps all started to get regulated, but people didn’t have records. Who knows what dumps are around the place that might cause some troubles in the future?”

Highbury Landfill Authority chairman John Minney said it was absolutely clear that the disturbing case of a sinking home showed development must be restricted around old dumps.

While the controversy over an ultimately shelved housing development around the Highbury dump ended in 2018, when the state government ­finally quashed a decade-old rezoning proposal, the future of the dump itself is undetermined as decomposing rubbish still produces methane.

“The Tea Tree Gully council at one stage wanted to rezone the Highbury Landfill land, but we said no because all the risks were too high,” Mr Minney said.

“The EPA (Environment Protection Authority) and the (state) government backed that (not going ahead) … it would be a very risky business to build on a dump.”

The Highbury Landfill Authority looks after the site for its remaining three member councils – Walkerville, Burnside and Norwood, Payneham and St Peters. It ­reports to the EPA as it is a contaminated site under the Environment Protection Act.

The landfill authority has an environmental duty to manage the dump for at least another 15 years, ensuring it has minimal impact on the surrounding environment.

That includes landfill gas extraction, monitoring and monthly reporting to the EPA.

The landfill authority has an environmental duty to manage the dump for at least another 15 years, ensuring it has minimal impact on the surrounding environment.

Plans for a solar farm on the site have been put on old because the land “down in the valley there doesn’t get enough sun to make it viable”, Mr Minney said. But that could change as solar technology improves.

Methane from multiple bores is piped to a flare and burnt off, rather than using it for energy, because it’s no longer flowing consistently.

McMahon Services Australia, through its subcontractor Biogas Systems, is contracted to manage the gas field and flare the landfill gas 24 hours a day, seven days a week. At one stage the flare used to run 10 hours a day.

Over time the site will stabilise as the gas dissipates. Mr Minney expected the site would eventually be turned into a public park.

The EPA said change to a “more sensitive” land use, such as a park, would require a contamination audit and other planning conditions. Construction was not usually ­allowed on dump sites, it said.