An Alkane Resources subsidiary has pleaded guilty to two counts of polluting waters at its mine south of Dubbo and is now awaiting its sentence.
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Tomingley Gold Operations Pty Ltd was charged after sediment from its activities entered a clean water drainage channel during rainfall and ran on to public and private property.
There was no evidence of any dead aquatic organisms as a result but there was potential for the sediment-laden water to cause harm, a statement of agreed facts shows.
The matter prosecuted by the Environment Protection Authority (EPA) was mentioned in Dubbo Local Court before magistrate Philip Stewart this week.
The maximum monetary penalty the Local Court can impose for the offences under the relevant section of the Protection of the Environment Operations Act 1997 is $110,000.
The offences occurred on or about March 7 and March 24-28 last year, two months after Tomingley Gold Operations started mining at the site, the statement of agreed facts shows.
The waters polluted included a drainage channel running through the eastern side of the mine, "designed and constructed to ensure flows of surface water" to a neighbouring privately-owned property "were not reduced".
"It was not intended for this surface water to carry a sediment load higher than that found in the pre-mine environment . . ." the statement of agreed facts shows.
At the time of the offences a central drain had been constructed but the defendant had not completed or implemented aspects of the surface water infrastructure and sediment and erosion controls, the statement shows.
There was a significant dry period before the rainfall events that caused the offences - on March 6 the mine recorded 24.9mm within a 20-minute period.
Prior to the rain mine employees had been focusing on minimising dust emissions and water supply shortage issues at the mine, the statement shows.
After the second offence Tomingley Gold Operations put in emergency temporary stabilisation and sediment control works, completed by April 1, 2014, and undertook rehabilitation of the areas impacted by the sediment discharge.
On September 18 the EPA issued a notice for the defendant to remove "the discharged sediments deposited from 20m either side of the Newell Highway reserve".
The defendant confirmed in a letter on October 9 it had completed the clean-up works in accordance with the notice.
The concentration of the total suspended solids (TSS) in the water was "elevated well above background levels" and the levels authorised under the licence limit, the statement shows.
"There is no evidence of actual environmental harm in the form of dead aquatic organisms from the incidents," the statement shows.
"There was potential for the sediment-laden water with high TSS concentration levels and turbidity to cause harm to any aquatic plans and animals living in the dams by the reduction of light penetration and interference with food conditions and feeding mechanism. "The potential harm was localised to the dams."
Tomingley Gold Operations has no prior convictions and entered a guilty plea at the earliest available opportunity.
The defendant established and contributes to the Tomingley Gold Project Community Fund, which is used to support projects that promote within the Dubbo community economic development, community connectivity, education and training and community infrastructure, the statement shows.
The matter has been adjourned to July 16.