The dump truck was reverse parking when it hit the front of the parked truck.
The operator misjudged the reverse angle and made contact at low speed.
The NSW Resources Regulator said the incident was not immediately reported by the supervisor to the open cut examiner.
"At the point of impact, a worker was on an access ladder and was unable to alert the operator to the pending collision," it said.
The regulator said workers must report incidents to supervisors immediately.
"Contract supervisors must be informed of escalation and reporting requirements," it said.
"When designing park-up areas, scenarios where vehicles can collide should be considered and controls such as drive-through park-up bays included in designs."
