The company pleaded guilty in the Land and Environment Court on August 16 of breaching section 120 (1) of the Protection of the Environment Operations Act 1997.

In addition to the fine, the Rio Tinto subsidiary has been ordered to pay legal costs of $51,000 and print a notice of the decision in a number of publications.

The incident occurred between February 1 and 5, 2012, when heavy rain produced run-off from the Hunter Valley mine’s visual bund.

The run-off was discharged from the mine’s boundary, but flowed onto adjacent property owned by Coal & Allied, where it entered a drainage channel and a number of intermittent water bodies before entering the Hunter River.

“The defendant is liable by reason of its status as occupier of the premises,” the judgment said.

“The pollutant was sediment and the offence occurred because the defendant failed to have in place adequate sediment and erosion-control measures to prevent the sediment entering the waters.”

The judgment said the company had installed control measures but they were unable to prevent the incident. Since then, “it has recognised that it needs to be more proactive in adopting risk management strategies which will assist in decreasing the likelihood of it being responsible for another environmental incident.”

“A number of measures and procedures have been, and are in the process of, being implemented, including techniques to achieve stabilisation and reduce erosion upon the bund when traditional stabilisation methods of top-soiling and seeding proved ineffective during the incident,” the judgment said.

The maximum penalty for such an offence is $1 million but the court ruled that “no actual or potential harm was caused by the offence” and “it is unlikely that such an incident will recur given the defendant’s strong commitment to preventative measures since the incident.”