The $235 million upgrade promoted as the solution to the North East's rail issues may be nothing more than a medium-term fix.
An independent review of the project conducted by Monash University was never publicly released, but Senator Janet Rice has revealed some details that "disturbed" her.
She grilled Australian Rail Track Corporation chief executive John Fullerton in Senate Estimates this week.
The Monash review found the $235 million in federal funding would only be enough if "uncertainties and constraints" were overcome by more rail works and negotiating with V/Line "to achieve common agreement on a realistic acceptance level" of the class 2 track.
The "preferred option" would have been targeted ballast cleaning and drainage remediation, but the $235 million was not enough.
"It is felt that this heavy investment in ballast alone will provide a medium-term solution, as there is a risk that the additional new ballast will become fouled and lose it's stabilising capacity, particularly in areas containing highly-fouled ballast and/or developing mud holes," the review stated.
"This highlights the fact that there is insufficient budget to undertake a complete upgrade of the (North East rail line) and that compromises need to be made."
Senator Rice asked if Mr Fullerton agreed that "the $235 million is giving you is a medium-term solution but it's not the full solution to the upgrade of the line?".
He said the Monash review did not dispute the ability of the ARTC to achieve its goal of upgrading the rail line.
"The $235 million is enough to get it to class 2 standard, but there are potential issues with the ongoing works that are going to be required," he said. "That was the objective: to achieve improved ride quality and ride comfort, improved reliability and improved resilience of the track."
Mr Fullerton revealed he expected the ARTC's $6-7 million maintenance costs to rise to cover the extra work.
"I'm really disturbed, given we were essentially promised that the $235 million was going to fix the track, that what we're hearing now is that it's not," Senator Rice said.
"I know the concern of the community is that a huge amount of money and a huge amount of work has been done on this rail line over many years, and yet we are still in a situation where it is of inadequate quality for high-quality rail services."