These costs were first raised by the project’s builders. Transurban is passing them onto the state government under the terms of their private-public partnership deal. The claims do not necessarily reflect the final cost of the project,which would be negotiated with the builders and the government.

An Andrews government spokeswoman said no claims on the project have been accepted. “Claims are made by construction companies all the time,” she said. “We have a fixed-price contract with Transurban to deliver the West Gate Tunnel project,and we’ll be holding them to that contract.”

A Transurban spokeswoman said it was “not unusual for contractors on major infrastructure projects to encounter challenges and to put forward claims to advance their commercial position”.

“That doesn’t mean those claims are accepted. The three project parties are currently involved in legal and commercial processes to resolve these matters and discussions remain commercial-in-confidence.”

Transurban estimates the cost of the project’s PFAS problem is $3 billion to $3.3 billion,while $1 billion has been attributed to challenges in relocating pipes for major utilities.

Late last year,the Andrews government reached an agreement with the builders of another of its major infrastructure projects,the $11 billion Metro Tunnel,to split the cost of a$2.7 billion blowout. This followed months of negotiations,with thebuilders making ambit claims of a $3.3 billion blowout and 18-month delay.

The leaked West Gate Tunnel documents also reveal the Andrews government is in a dispute over delays in constructing a bridge over the Maribyrnong River connecting the tunnels with an elevated road above Footscray Road.

Chinese-owned John Holland and Spanish-controlled CPB Contractors are refusing to carry out these works until an agreement on cost blowouts is reached.

Separate project documents leaked toThe Age reveal new details about the planned management of the huge amounts of rock and soil being dug up to build the twin road tunnels beneath Yarraville.

Once the wet dirt is excavated by the tunnel-boring machines,it will be transferred on a conveyer belt to a dedicated “bin” at a large spoil handling shed on Whitehall Street,Yarraville.

Each tunnel will have its own bin,which will be large enough to store thousands of tonnes of soil being dug up over a maximum two-day period.

Excavators will then transfer the soil from the bins onto trucks,which will make up to 15 trips an hour over 24-hours,seven days a week,for two years.

The trucks transferring the soil to approved landfills will follow specific routes. They will be sealed to prevent leaks,as the soil will be 50 per cent water. The truck’s details,the time and date the truck was loaded and the source of the material will be recorded.

RMIT’s director of urban research Jago Dodson said major transport project costs were typically “low balled” initially and tended to blow out during construction,raising serious questions about their benefits to taxpayers.

A fresh business case of the West Gate Tunnel that factored in cost overruns would prove the project was “not viable,from an economic point of view,” he said.

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