Oliver fell into a sinkhole outside his school. Now there’s fears more old goldmine shafts could open up

When Oliver McDonald fell into a sinkhole only 50 metres from his primary school in Ballarat late last year, the nine-year-old “laughed it off”. But his dad, Shaun, wasn’t amused.

“I got a call from my ex-partner, they were walking to school … Next thing, he had just disappeared,” Mr McDonald said.

“She looked down and the only thing that had stopped him from going down was his backpack.”

Fortunately, Oliver was not injured when he fell into the sinkhole along Edwardes Street, near Black Hill Primary School.

Mr McDonald said that nine months later, the hole had not been repaired and its edges were crumbling, creating an even bigger cavity.

“I contacted the local council and they said they would organise something. An hour or two later nothing had been done,” he added.

“It could be very dangerous … It’s not just the one, there are going to be more popping up around that area.”

Sinkhole to be repaired 

Since asking the Ballarat City Council about the sinkhole, the ABC has confirmed contractors will undertake repairs immediately on the Edwardes Street sinkhole. 

City of Ballarat director infrastructure and environment, Bridget Wetherall, said the sinkhole had been caused by “a leaking underground pipe”.

“It has been assessed and it has been determined that there is no further risk of it worsening,” she said.

“Temporarily filling the sinkhole with soil before the pipe was repaired … could have caused it to re-open.”

Ms Wetherall said the council was working through a “backlog” of priority jobs stemming from last year’s record rainfall.

“Contractors have been engaged to complete repairs to the damaged pipe and work is expected to be completed in the coming days,” she said.

Another smaller sinkhole on Chisholm Street, around the corner from Edwardes Street, has been cordoned off.

Digging into Ballarat’s history

According to information from Victoria’s Department of Environment, the sinkhole is adjacent to a nearby historic gold mine.

Situated near the Black Hill Primary School, the gold mine was started in the 1860s by Crocodile Co. 

The open-cut mine, as seen on an interactive map Gold Maps Online, produced nearly 600 ounces of gold. It’s unknown when the mine was decommissioned. 

In 2007, a Ballarat East man returned home from shopping one day to find his backyard had completely caved in, due to an old mine shaft located below his property.

‘We have no idea where they are’ 

Federation University’s lecturer in applied geochemistry and economic geology, Haydn Swan, said historic mines could be difficult to “deal with”, as the shafts were often small and hard to locate.

“There are some exposed outcrops at the Black Hill school oval, which suggests it has been excavated,” Mr Swan said.

“All of the deeper mines, they’ve usually left voids at depth and put a cap over the surface. And, if they were old enough, the cap would’ve been timber, which obviously would not last forever.

“Anywhere north of Buninyong to Invermay, there’s potentially lots of smaller ones [but] we have no idea where they are.”

Retired mining engineer and former senior lecturer at the Ballarat CAE, Peter McCarthy, said rain and strong weather could make old mine sites vulnerable to shifting soil.

“If holes like that appear, they are almost certainly related to the old gold mining activity,” Mr McCarthy said.

“They could be related to small shafts that individuals sunk even in the 1850s, because there was quite widespread shaft sinking at that time.”

In 2022, Ballarat saw 840 millimetres of rain in total, with 106mm falling in August. The highest daily rainfall total was in October, when more than 50mm of rain drenched the city in just a few hours. 

Mr McCarthy said that during his 40-year career, he would see one or two collapsed shafts per year.

“It does depend on rainfall, if it’s a wet year then you tend to get more of them,” he explained.

“And the liability really varies, but usually it’s with the landowner.

“So if you own a block of land and it’s got a shaft, you’ve got to fix it up yourself.”

The ABC has contacted Black Hill Primary School for comment.