After a succession of delays and dramas, Snowy Hydro has been forced to acquire an additional tunnel boring machine to make sure the $12 billion Snowy 2.0 pumped hydro project is completed on time.
Repeated problems with an existing machine named Florence, combined with "initial design immaturity" to deal with geologically complex terrain, prompted the re-calculation of what it would take to complete the tunnelling works.
Snowy 2.0's costs have already blown out by $10 billion and its start date pushed back six years.
Acquiring the extra tunnel boring machine will cost around $75 million, but Snowy Hydro is confident it will not need additional funding and can still meet its amended time frame of completing the project by December 2028.
The complexity of the geology has been long known, but Snowy Hydro CEO Dennis Barnes said recent additional surveying of a fault zone confirmed the need for another machine.
"We've carefully considered a range of options to get through the fault zone and overcome the initial design immaturity," he said in a statement.
"Bringing in a fourth machine is the best way to keep the Snowy 2.0 on track for its target completion date."
Boring purchase prompted by disappointing performance
Mr Barnes acknowledged the disappointing performance of Florence, which was being relied upon to excavate a 17-kilometre tunnel linking the upper Tantangara reservoir to the underground power station, was a factor in the decision.
"It's difficult to say with certainty whether the same action would be needed if Florence had performed as we had hoped," he said in a statement.
"However, it's likely that the fourth machine would still be needed."
Florence spent most of 2023 bogged in soft ground, triggering a sinkhole to open up in Kosciuszko National Park.
Earlier this year, it became jammed in hard rock, making only incremental progress on what is the longest and most technically challenging part of the project.
The use of a fourth machine — to begin boring from the other end of the tunnel from Florence — is subject to the NSW government approving Snowy Hydro's submission to modify its environmental impact assessment to account for the change.
Six years late and six times more expensive
The Snowy 2.0 project involves building an underground hydropower station in the heart of Kosciuszko National Park, with 27 kilometres of tunnels linking Tantangara Dam high up in the mountains to Talbingo Reservoir lower down.
Once completed, 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 first announced by the Malcolm Turnbull government in 2017, it had an estimated cost of $2 billion and was expected to deliver its first power in 2021.
Since Malcolm Turnbull's announcement to expand the Snowy Hydro station, its timeline has blown out by six years, and it is now expected to cost $10 billion more. (AAP: Alex Ellinghausen)
A succession of cost blowouts and time delays mean it is now slated to cost $12 billion and deliver its first power in late 2027.
There have been a series of safety issues including toxic gases filling the tunnels during construction, as exposed last year by the ABC's Four Corners program.
Fourth borer will need a name
There are already three tunnel boring machines in use on the project: 'Florence,' named after Australia's first female electrical engineer Florence Violet McKenzie, 'Kirsten' for astrophysicist and science communicator Kirsten Banks and 'Lady Eileen Hudson' in honour of the wife of Snowy Hydro's inaugural commissioner Sir William Hudson.
It is a long-standing tradition to give tunnel boring machines female names before they commence work.
Snowy Hydro's board chose the name Lady Eileen Hudson, while Florence and Kirsten were selected from a shortlist by local students.