John Henry Rooney made at least 1000 shafts safe in Bendigo and as far away as Ballarat and Stawell during the first half of the 20th century.

His is one of the stories local historian John Kelly has dug up for his upcoming book Danger Below: Making Bendigo Safe.

The book would have been released this year if it had not been for the coronavirus pandemic.

Those plans are on hiatus but Mr Kelly has dug up one of the stories that will feature in the book.

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Rooney died trying to cap a mine shaft in California Gully.

He was likely standing 10 to 12 feet in the shaft in order to prepare the site for the nine inch thick concrete cap when it happened, Mr Kelly said.

"He would have chipped away at the dirt ... until he had a nice solid base."

A boulder is believed to have come loose and swept him down into the deep.

It took a team four days to recover his body because of the amount of debris that landed on top of him, Mr Kelly said.

About 6000 mine shafts were sunk in Bendigo's gold fields from the middle of the 19^th century onwards.

Many were effectively abandoned, Mr Kelly said.

Departing miners only had to make the land look natural again, so shafts were often covered with a bit of timber, metal and dirt, he said.

Eaglehawk's council became so concerned that it began lobbying for action in 1913.

"There had been a lot of accidents. Boys were bird nesting, girls were collecting ferns and they were ending up down the shafts," Mr Kelly said.

it was not just children falling down them, though.

Rooney himself saved a woman who fell 85 feet down a California Gully shaft in 1922.

Mines were often dumping grounds and it is likely that at least a few of those who fell in had gone there to get rid of rubbish, Mr Kelly said.

Rooney was employed in 1925 to deal with the problem, when Eaglehawk and Bendigo's councils took action with the help of the state's department of mining.

It is unclear exactly how many shafts he and his teams made safe over the next 15 years but Mr Kelly says it would likely have been more than 1000.

Many were shallow enough they could be back filled but quite a few needed to be capped with concrete.

Capping continued after Rooney's death, with two others overseeing works well into the future.

Both of their stories will also be covered in Mr Kelly's book when it can finally be published.

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Workers must still cap mines under buildings and roads today.

Last September, three dormant mining vents collapsed under Napier Street and the road started sinking.

It happened shortly after the road was reopened following major road works.

Neither had been found before or during the roadworks, despite others being capped during "extensive investigations", a government spokesperson said at the time.

It did not surprise La Trobe University engineer Chris Stoltz.

"That knowledge depends on how well historic mines' locations were recorded and how well maps were maintained," he said.

"I remember years ago some friends of mine from Kennington noticed their lounge room floor was a little spongy. They got a builder to climb under the house, who took one look at it and said a mine had opened up.

"So it can happen anywhere in Bendigo."

Mr Kelly warned that many concrete caps over mine shafts are getting weaker.

Many of those installed in Rooney's time were nowhere near as thick or well engineered as those that are installed today.

"You think about all those caps that Rooney did, and the specifications they used, and really we are waiting for them all to give way," Mr Kelly said.

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