A subsidiary of Rio Tinto has received a reasonable fine after it was found to have dumped several megalitres of contaminated water into a New South Wales river.

Coal & Allied, an adjunct of Rio Tinto, has been hit with a $45,000 bill after six megalitres of sediment-laden polluted water from its Mt Thorley-Warkworth mine flowed into a Hunter River tributary. Reports in a local newspaper said the water flowed into a drainage system, which then flowed into Salt Pan Creek, Newport Lagoon, Wollombi Brook and finally into Hunter River.

Local conservationist and Bulga-Milbrodale Progress Association spokesman John Krey says the fine is more than fair: “this was a major pollution incident and it’s good to see they have been held to account... Mines have to pay more attention to their controls, they are too slack when it comes to dust and noise and now we have seen a serious water pollution incident as well.”

Coal & Allied was found to have violated section 120 (1) of the Protection of the Environment Operations Act 1997 after entering a guilty plea in the Land and Environmental Court. The ruling also forced the company to publish its error in newspapers this week.

A spokesperson was quick to down-play the breach, saying “Coal & Allied regrets that during a heavy rainfall event in early February 2012, non-mine affected water containing soil from civil works associated with the erection of a visual bund (as required under Mt Thorley’s Approvals), exited Mount Thorley Operations’ western boundary and flowed into land owned by Coal & Allied.”