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A fresh crisis has hit the beleaguered Snowy 2.0 hydropower project, with part of a tunnel collapsing and boring machine "Florence" once again struggling to progress through difficult geological terrain.
On Monday, "drill and blast" tunnelling activity in the main power cavern of the project caused a collapse in an adjacent tunnel, called the Main Access Tunnel.
Three sources connected to the construction project have told the ABC that concerns were raised before the collapse about the proximity of the drilling and blasting to that access tunnel.
The collapse raises questions about the safety procedures for tunnelling and why blasting for one tunnel was happening so close to another.
In a statement, Snowy Hydro said it had always planned for the cavern to connect to that part of the main access tunnel, but not that quickly.
"The 'breakthrough' occurred … one blast earlier than planned," the statement reads.
"This was a recognised risk associated with blasting in the area and appropriate safety measures were in place. This included bracing of the concrete segments to ensure the tunnel is stable while excavation … is undertaken.
"There were no workers underground at the time of the blast. It is a safety measure that no workers are allowed in the tunnel during blast activities."
The main access tunnel remains closed until the connection between it and the main cavern is completed.
One person involved in the construction project said at the time of the collapse, the sections subject to active drilling and blasting were larger than normal to speed up the excavation.
"They are that far behind, they are cutting corners," they said.
Snowy Hydro did not answer specific questions about this allegation.
Safety fears compound
Other safety concerns have been raised about the handling of high-pressure water equipment at another worksite in the Snowy 2.0 project.
A coupling joint on a pipe at the Tantangara construction site failed when it was re-pressurised after repairs on a different section.
The burst pipe caused further delays to construction and raised significant safety concerns, with SafeWork NSW carrying out an inspection.
"Principal contractor Future Generation took the appropriate action to stop work on all dewatering pipes across the project until all couplings were checked," Snowy Hydro said in a statement.
"The health, safety and wellbeing of people is paramount to Snowy Hydro. We continue to work actively with Future Generation and our safety regulators to protect the health and safety of all workers and visitors on the Snowy 2.0 sites."
It follows a series of issues that SafeWork NSW have examined, including one incident where a tunnel filled with toxic gas.
The ongoing safety issues are frustrating the project's workforce.
"This is just another f*** up … it's comical how bad [the contractors] are," they said.
The ABC asked Snowy Hydro several questions about the latest safety concerns, but had not received a response by the time of publication.
From soft ground to hard rock, Florence the machine faces new troubles
The Tantangara construction site has been beset with problems ever since the tunnel boring machine there, named Florence, got bogged in soft ground for the better part of a year.
Now, Florence has struck new problems, but this time it is solid rock that is causing problems.
The hard rock Florence is currently boring through takes longer to grind and has meant the cutting heads have had to be frequently replaced, causing the entire operation to halt while that happens.
After making reasonable progress in March, the slow grinding and frequent stops have seen progress fall by more than two-thirds in April.
Florence grinds a passage 2 metres deep in the rock, which is then lined with a "ring" of nine concrete segments before all the machinery is inched forward to start the cycle over again.
In March, Florence progressed by 115 rings. In April, it dropped to 32 rings for the month.
In a statement issued on Thursday, Snowy Hydro said Florence remains "fully operational" and has now excavated more than 800m of ground at Tantangara.
Florence is meant to grind out the longest tunnel in the Snowy 2.0 project, the 16-kilometre "headrace" that connects the Tantangara Dam to the main power cavern.
Even if progress picks up again soon, it won't be enough to meet the revised deadline of having Snowy 2.0 generate its first power by late 2027.
In February, Snowy Hydro CEO Dennis Barnes said a decision would be made "in the next month or two" about whether to purchase another tunnel boring machine to start tunnelling from the other end. A "drill and blast" approach from the other end was also under consideration.
But a decision has not yet been made on how to progress.
"Snowy Hydro has been investigating options to de-risk the headrace tunnel construction by excavating from the other end. This work remains ongoing," the Snowy Hydro statement reads.
Snowy 2.0 critical for transition to green electricity grid
The Snowy 2.0 project has been mired in controversy since its inception.
The project involves building an underground hydropower station in the heart of Kosciuszko National Park, with tunnels linking Tantangara Dam high up in the mountains to Talbingo Reservoir lower down.
It will be able to generate 2,200 megawatts of power when water flows from Tantangara to Talbingo, which can be used on demand to support the variable contributions of other renewable energy sources to the power grid.
When electricity prices are low, water will be pumped back in the opposite direction to "charge" what is essentially a giant water battery.
The project was initially estimated to cost around $2 billion when announced by then prime minister Malcolm Turnbull, and to be up and running by 2021.
It is now expected to cost $12 billion and be operating in 2027, with the Commonwealth-owned Snowy Hydro now bearing most of the cost and risk after the initial fixed-price contract was abandoned.
Snowy 2.0 is a key part of the transition of the electricity grid to renewable resources, as its ability to operate on demand is needed to "firm up" more variable renewable energy sources like wind and solar power.