Orica has pled guilty to breaching its environmental protection licence last year after a series of spills and safety incidents.
The explosives manufacturer appeared in the NSW Land and Environment on Friday regarding charges that it failed to run its Kooragang Island ammonium nitrate plant competently, according to The Newcastle Herald.
This guilty plea relates directly to an incident in March during which it discharged chemicals into the nearby Hunter River.
"The EPA alleges that this resulted in ammonium nitrate being discharged into the air across Kooragang Island and the Hunter River," the EPA said.
"It is alleged that the discharge lasted for around 40 minutes and caused nearby workers at Mayfield Wharf to cease work and take shelter indoors."
It comes after a number of other safety incidents late last year, beginning in August when the company recorded a hexavalent chromium leak.
From that time it suffered a number of issues, including further chemical leaks, nitric acid leaks, and equipment issues when it attempted to restart its plant.
In April Orica announced that it would be expanding its manufacturing operations at the site, on top of approvals already granted in 2009.
It will return to court this month to face charges relating to the leaks.