According to a report by the NSW Resources Regulator, the driver failed to notice the ground was unstable and reversed into the dam wall before the left-hand side of the truck sank.

The truck was stuck fast and had to be towed out of the area.

Mine operators have been put on notice by the regulator to check dam wall design, construction methods and procedures when constructing dam walls.

That includes consideration of the strength, size distribution and consistency of the materials to be used.

There should also be geotechnical consideration of the potential for slumping after significant rainfall events.