QUEANBEYAN City Council face a maximum penalty of $1 million relating to incidences on November 4 and 5, 2007 when about 1.5 million litres of untreated sewage was released into the Queanbeyan River.
The council is being prosecution by the Environment Protection Authority for the pollution of water under section 120 of the Protection of the Environment Operation Act 1997.
The council is only being charged for the second incident on November 5 and have pleaded guilty to the charges.
General manager Gary Chapman said he expected the fine to be in the "tens of thousands".
"I don't think we will receive the maximum fine, in the grand scheme of thing this is a minor event...
there was no environment impact unlike an oil spill. There's no on-going effect. It was a minor event with minimal impact on the environment."
Mr Chapman said ratepayers wouldn't be affected if the council were fined as there is $40 million in their sewage fund.
The leak occurred when the sewage pumping stations located at Morisset and Wanniassa Streets failed.
At the time, it was reported that severe rainstorms paralysed facilities at the plant and shut down the alarm system that would have informed council staff of the spill.
Council was not aware of the problem until a pedestrian had noticed the sewage which had covered an area of land and reed bed before reaching the river.
In 2007, council blamed their slow reaction on the failure of a Telstra SMS paging system.
Mr Chapman said the communication system in an event of a spill was reviewed. The general manager and mayor would be notified of any spillage the following day. In the case of a major spillage it would be appropriate to contact them immediately.
"We have changed the procedure, I or the mayor would not appreciate being contacted in the middle of the night for every spillage, minor spillages happen all the time," he said. "A major spillage is anything that would have a major impact on the environment...the one we had in 2007, we don't get that all the time and we haven't had one since.
"In court documents, the EPA said the respective failure of both the pump and alarm systems had been the cause of the major overflow of the untreated sewage into the river. This, and the delay in repumping, were said to be important reasons why the prosecution was instituted.
The EPA could not comment any further on the matter as it is currently awaiting judgment from the court. A judgement date is unknown.