The coal company has already spent $250,000 on clean-up and rehabilitation from the start of the incident on August 18 to late November that year.

Centennial Newstan’s prompt and adequate response to the environmental incident was well received by the state’s Land and Environment Court, which could have penalised the coal miner up to $1 million.

While the colliery long had the practice of discharging water into old mine workings, there was no intention to discharge the black-grey water which contained coal fines from a pipeline into a nearby unnamed creek.

The discharge of up to 1.8 megalitres formed a big plume and subsequently extended into Stony Creek and an area of wetlands.

The court found the unintentional discharge occurred because the level of groundwater in the old mine workings rose above the invert level of the pipeline.

The court said the cause of the sediment in the water was unknown.

Both the prosecuting Environmental Protection Authority and Centennial agreed that a geological event, such as a roof or pillar collapse in the old workings, might have caused the discharged water to contain the coal fines.

Centennial was also ordered to pay a total of $38,500 in prosecution and investigation costs, plus the expense of taking out advertisements in newspapers to acknowledge the conviction.

Longwall mining ceased at Newstan in April 2009 with the mine placed on care and maintenance the following month.