It comes after the company has been in the spotlight for its hexavalent chromium leaks at its Kooragang Island nitrates plant.
The leak reportedly happened between midnight on Monday and 9am yesterday.
“The emission was detected by an air monitor that has been placed adjacent to the site in close proximity to the residential area to monitor potential emissions from the site,’” Greg Sullivan, deputy chief executive of environment protection and regulation at the OEH, said
“The exceedance was linked to an incident involving the soil remediation process. OEH has issued Orica with a notice and also required Orica to immediately notify residents of the incident and report to OEH by 5pm today that this action has been taken,” he added.
According to Orica, the meter recorded levels in excess of the 30 minute average compliance level of 1.8 micrograms/m3, peaking at around 4 micrograms/m3.
It says it will carry out investigations into the cause of these elevated levels mercury vapour, and has begun door knocking to alert nearby residents.
Orica has been working towards cleaning up mercury from its site near Botany Bay.
Orica spokesperson Nicole Ekert told Australian Mining at the time that while its soil washing effort at Botany Bay had been successful in pilot trials it had not worked in the larger operation.
“Unfortunately the soil washing technology in a full scale plant has not been able to sustain adequate reliable operation and Orica has decided to suspend the works,” she said.
She said the company understood the community concern the chemical leaks had caused.
The NSW health director, public health unit, south eastern Sydney Illawarra, Mark Ferson, said NSW Health is working with the OEH on this issue.
Ferson went on to say that “as mercury vapour is heavier than air, it is unlikely that the vapour would have travelled very far from the site. Any mercury would have remained close to the ground before dissipating.
“Health effects associated with mercury vapour occur after immediate high levels of exposure or long term chronic exposures, neither of which occurred in this instance.
Sullivan added that the release is not expected to have any impact on the health of local residents, stating that “the level of exceedance last night was well below a level that is known to cause immediate health effects. Including levels measured last night and known levels measured over this year, the possible exposure of residents to mercury is well below the World Health Organisation annual average guideline”.