The Environment Protection Authority (EPA) levied the fine on West Cliff Colliery at Appin over discharge of ferric chloride into a section of the Georges River that also left the water acidic.

“Sampling by the EPA at the time of the alleged incident showed that the river close to the discharge was acidic and had elevated turbidity with high levels of dissolved iron and zinc,” EPA Illawarra region manager Peter Bloem said.

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“While on this occasion no dead or injured animals were observed, the discharge was at levels that are toxic to aquatic species.”

The incident occurred on October 18-19 and, according to the EPA, the environmental effects were limited due to quick action from Endeavour Coal, the presence of a river rock pool that allowed the discharge to be pumped back to the colliery and a rainstorm which diluted the remaining pollutants.

The EPA said the incident happened when a sediment pond at the site became overdosed with ferric chloride – which is used to treat and clarify water.

The water was then discharged into the river.

Mr Bloem said follow-up tests two weeks after the initial EPA inspection showed water in the affected area was clear, and small fish were observed in the river.

“Endeavour Coal carried out remediation work and has undertaken to improve its maintenance, monitoring and warning systems,” Mr Bloem said.