The cost of Melbourne’s West Gate tunnel project could blow out to nearly $10 billion, according to a report.

Already delayed because of a dispute over contaminated soil from the construction site, the project now might cost an extra $3 billion.

Leaked state government reports reveal the extent of the overruns, according to The Age.

The project already is costing $6.7 billion and a third of the overruns are said to be linked to problems with underground pipes.

The project’s builders already have pushed to rip up their contract, sending a legal dispute to arbitration.

It is meant to be an alternative to the city’s heavily congested West Gate Bridge but it has been delayed amid the ongoing fight over PFAS-contaminated soil at the construction site.

Toll giant Transurban took CPB Contractors and John Holland to Victoria’s Supreme Court after the builders asked to be let off their end of the bargain.

At least 200 workers on the project have lost their jobs since January because of the delays. The project is now due to be finished in 2023, a year behind schedule.

According to a report in the Herald Sun on Tuesday, taxpayers will be slugged hundreds of millions of dollars for the contaminated soil to be moved and stored.

There are two proposed sites for the contaminated soil.