The West Gate Tunnel builders had no clear plan for disposing of the 2.3 million tonnes of soil removed from the construction site, even as tunnelling was due to begin.

Leaked documents from the builders show they had not settled on a transport plan or a dump site for the soil as late as last October, two months after Premier Daniel Andrews said digging was about to start.

It can also be revealed that three councils – Melbourne, Maribyrnong and Hobsons Bay – warned that contaminated soil would be dug up along the $6.7 billion toll road connecting the West Gate Freeway in Spotswood and CityLink in Docklands and stricter controls were needed.

The project's builders, John Holland and CPB Contractors, now want to ditch the project, alleging the amount of contamination with PFAS – a group of potentially carcinogenic chemicals – was underestimated when they signed the project's $5 billion construction contract.