AGL has been fined $15,000 for air pollution offences at Liddell Power Station.
The power station exceeded the licensed solid particles concentration limit for emissions from one of the power station's four boilers in August to September 2020.
AGL's Environment Protection Licence sets specific limits for the emission of pollutants from the boiler units.
The power station, which recently celebrated 50 years of operation, is due to close in stages across 2022 and 2023.
Along with the fine, the EPA also issued AGL with an official caution for an exceedance on a separate one of the four boiler units around the same period.
Director Regulatory Operations Adam Gilligan said the EPA had required AGL to carry out rectification works to help prevent a similar incident in the future.
"This alleged outcome should serve as a reminder that environmental incidents such as these can come at a significant cost," he said.
"Solid particle emission limits are set for good reason - to help prevent air pollution incidents and possible environmental damage."
"Our licensees have an obligation to comply with their licence conditions. Best practice and cleaner production leads to improved environmental outcomes."
An AGL spokeswoman said the company had proactively made repairs and modified operations to rectify the cause.
"AGL takes its environmental obligations seriously and works cooperatively with all regulatory agencies to ensure we meet all requirements and engage with the communities where we operate," she said.
"AGL's decarbonisation strategy is clearly set out in its Climate Statement, including the commitment to net zero emissions by 2050 and the commitments to exit coal-fired power."
