The company told the Environment Protection Authority that an emergency valve on the pipeline had been tampered with and left open.

The waste contained flotation tailing slurry – a byproduct of the gold mining process.

The slurry flowed to a private property about 450 metres east of the discharge location, affecting dams and Crown Land along the way.

The EPA took samples from the company’s McCormick’s Road site in Fosterville.

EPA north west regional manager Scott Pigdon said it was a preventable incident.

“The EPA officer observed there were no controls in place to prevent tampering with the valve and to prevent a discharge from occurring,” he said.

“This incident could have been prevented, or at least minimised if the duty holder had installed controls on the emergency valve to prevent un-authorised persons tampering with it.

“When released into native forest and privately owned land, the slurry had the potential to significantly impact both land and waterways.”