Centennial said the fine reflected the severity of the incident.

“From the day of the incident, Clarence took responsibility for rectifying the environmental damage caused and engaged a specialist environmental clean-up team,” it said.

“This team oversaw an extensive clean-up operation that operated for 12 months in extremely rugged conditions costing $2 million.”

The land based clean-up within the colliery was completed within three months and the area has since been rehabilitated. The clean-up in the Wollangambe River continued for a further nine months and was finalised in July 2016. 

“Clarence fully cooperated with the Environment Protection Agency and the Office of Environment and Heritage responding to any orders issued during the clean-up and appreciated the oversight and cooperation of both agencies,” the company said.

“As required by the environmental protection legislation for incidents of this nature, both the EPA and OEH commenced prosecution proceedings [in May 2016] in the LEC [NSW Land and Environment Court] against Clarence Colliery, a subsidiary of Centennial Coal. 

“Clarence entered a plea of guilty to the charges at the earliest available opportunity.”

The company said that prior to this incident, Clarence had a clean record, with no conviction for any environmental offence.

In his judgment, Justice John Robson recorded that: “I accept that Clarence Colliery has demonstrated contrition and remorse concerning the offences and has, by its conduct, taken responsibility for its actions and acknowledged the environmental harm caused.”

Centennial Coal said both it and Clarence deeply regretted the incident and apologised for its occurrence and had taken steps to improve the way reject emplacement was managed on site to prevent a reoccurrence of the incident.