It was the start of night shift when the tunnel began filling with gas.
Workers going underground at the Snowy 2.0 site say they were told that there was nothing to worry about, that it was just water vapour.
But on that Saturday in early July, chemistry had finally caught up with them.
The previous year, the giant machine digging tunnels for the project had caused a sinkhole to open up.
Workers had spent seven months trying to stabilise the nearby ground, pumping in thousands of litres of grout, cement and polyurethane foam.
Now that foam had triggered a chemical reaction, producing toxic gas.
Snowy Hydro, owned by the federal government, has never disclosed this safety breach, even as it pumps out highly produced videos and press releases.
It was not meant to be this hard.
The pumped hydro project, trumpeted as a grand "nation-building" scheme, was first estimated to cost just $2 billion. It's blown out to $12 billion.
It was expected to produce its first power next year — now, it won't be keeping any lights on for at least another four years.
Snowy Hydro has revealed to Four Corners as much as $2 billion of this blowout can be blamed on the stalled tunnel boring machine they call Florence.
Its 15km journey below Kosciuszko National Park should be well underway by now, but it's gone just 150m.
Insiders say warnings were ignored — Florence was doomed from the start.
'Dare to dream'
At Florence's launch, in March 2022, then-Snowy Hydro chief executive Paul Broad was in an expansive mood.
"In life, you dare to dream," he told the assembled school children, mayors, and workers.
Launch day for Florence the tunnel boring machine.(Supplied: Snowy Hyrdo)
"You think about the kids and the world they are going to inherit."
Snowy 2.0 was sold as being key to a low-carbon future — capable of powering 3 million homes for an entire week.
Its vast network of tunnels and underground power station would only be possible, Mr Broad said, because they had hired the world's best tunnellers.
But even as local school children signed their names on the 2,400-tonne boring machine, those working at the site knew trouble lay ahead.
In the weeks before Florence was launched, workers had drilled ahead to explore the tunnel's planned route.
Four Corners has been told that around 100m in, they hit soft ground. Thousands of litres of water gushed out.
It should have been a moment to pause.
Instead, one worker says the hole was simply plugged and they launched Florence as planned.
Just eight weeks later, it hit the predicted soft ground and water. From that moment on, the machine was effectively bogged.
Water around the tunnel boring machine Florence after it hit soft ground.(Supplied)
"We would push forward 50cms then spend the next week clearing out all the mud and water from around the tunnel boring machine," one worker says.
"Sometimes there was 3 to 4 feet of water around the machine."
At the time, Snowy Hydro told the public nothing about these problems.
Florence and the slurry machine
In Snowy Hydro's words, Florence is "one of the most technically advanced machines in the world". With a price tag of more than $150 million, it's not just a tunnelling machine, it's a mobile factory.
But for the past 19 months, it's had little chance to show off. It's barely even moved.
The boasts are based on Florence's ability to operate in both hard and soft ground.
But to work in soft ground, a so-called "slurry system" should be in place, which helps shore up the ground ahead.
Not only was this slurry system not operating, its key equipment wasn't even on site.
Florence wasn't equipped for the soft ground ahead.(Supplied)
This went against the project's own guidelines for Florence, which state this system should have been connected for the "start-up length" plus the first 1km. The Construction Method Statement from August 2021 did state the final decision should be made based on the conditions at the time.
Snowy Hydro chief executive Dennis Barnes was appointed in February this year and has been tasked with turning around the troubled project.
He says the contractor Future Generation knew the ground was soft before tunnelling began.
"We just didn't know it was that soft," he says.
The project's original champion, former prime minister Malcolm Turnbull, is not convinced.
"Clearly, it's an oversight, it's wrong. I mean, if you're going to be dealing with soft ground that needs to be slurried and you don't have the slurrying kit, you've screwed up, haven't you?"
Future Generation says, "drilling in advance of the tunnel boring machine" confirmed its operation method "was appropriate".
It says "every measure" was taken to ensure the tunnel was excavated "with diligence, care and in the safest possible working environment".
Tonight Four Corners gets rare access, going inside Snowy 2.0’s tunnel, as it investigates whether the troubled project can be turned around. Watch from 8:30 on ABC TV and ABC iview.
Sinkhole
As winter turned to spring last year, rumours that Florence was in trouble began circulating.
Rather than levelling with the public, Snowy put out another press release.
"Florence on the move," it said.
Technically, Florence was still inching forward, but her performance was well short of the 30 to 50 metres a day it was capable of tunnelling.
Then, just before Christmas, Florence struck more trouble. Months of tunnelling through wet sandy soil had caused the ground above to collapse and a sinkhole to open up.
A 10-metre-wide sinkhole has opened up above Florence, stalling the tunnel boring machine.
Snowy had another chance to level with the public, but chose to put out a carefully worded corporate video:
"[Florence is] progressing steadily through poor ground conditions," it said.
Workers had warned a sinkhole was likely.
They had been telling the contractor the ground was too soft to continue the strategy of inching forward in the hope of hitting harder ground.
"Florence was pulling out triple the amount of soil it should have been," one worker says.
"We warned them it was going to cause a sinkhole, but they did not listen".
It wasn't until February that Snowy would finally concede Florence was "paused".
"It's a bit like the ad on TV, right, where the four-wheel drive is bogged and they're saying [it's just] parked," says Tony Callinan, NSW branch secretary for the Australian Workers' Union (AWU).
"[Florence] is not paused, it's bogged."
Energy investor Simon Holmes à Court says Snowy has "misled the public on a number of occasions".
"They got the cost wrong, the ground conditions, the time, the schedule, and I think the way they levelled with the public, they've got that wrong too."
"They've given us reason to believe that things are on track. When we later found out that they're not."
Toxic
There was no press release to notify the public when the attempt to stabilise the ground around Florence caused toxic gas to fill the tunnel.
The AWU says workers who refused to continue their shift that chilly July night were told that it was just water vapour. Only later was it identified as isocyanate, a hazardous chemical.
Snowy Hydro has never disclosed July's gas safety breach.(Supplied)
Dennis Barnes says nothing was hidden from the public.
"We wouldn't, as a matter of course, describe all of the work we're doing, whether it's proactive or reactive around safety," he says.
Work was stopped in the area for weeks.
"It's one of the only times where I've actually had a proper emergency, where the tunnel had to be evacuated," Mr Callinan says.
"I've seen many major projects and unfortunately, this job's one of the worst … sorry, it is the worst by far."
SafeWork NSW says the gas posed a "serious imminent risk" to "health and safety" while noting that Snowy 2.0 had "inadequate control measures … to prevent exposure to a harmful substance".
Four Corners asked the NSW regulator how many safety breaches there have been at Snowy 2.0.
It refused to provide the numbers, saying it may affect the contractor's reputation.
Uncertainty
Dennis Barnes insists Florence will be moving again very shortly. He says the ground has been stabilised and Snowy is just awaiting planning approval from the NSW government.
The federal government will be hoping he's right this time.
Back in May, Mr Barnes said Florence would be moving "in weeks, not months".
He now concedes that was "wrong" and says he was "somewhat naive and optimistic".
Snowy Hydro believes it will have Florence moving again shortly.(Four Corners)
But even if the machine does get moving in the next few weeks, energy expert Simon Bartlett says there's plenty of uncertainty ahead.
"They're going to encounter these poor [ground] conditions again and again and again," he says.
"Those places where it's similar and worse, I think there's quite a high likelihood we're going to see the same thing happen again."
This will play a big part in determining if the revised price tag of $12 billion and first power by 2027 can be achieved.
"We've done an incredible amount of work to verify those numbers and times," Mr Barnes says.
He says they still have some of the best contractors in the world on the job, they've done the planning and are ready to go.
He has faith in Florence.
Watch Four Corners' full investigation Tunnel Vision from 8:30 on ABC TV and ABC iview.
