AN INVESTIGATION is under way to determine the cause of a sodium hydroxide leak which occurred at QAL's South Trees Facility.
The incident took place on December 5 and involved one tank where a "slow leak" occurred.
A Queensland Alumina Limited spokesperson said the leak resulted in "an uncontrolled release of material within the bunded containment area".
Contrary to initial reports, the incident did not result in an explosion at the facility.
The alumina giant uses large tanks to hold sodium hydroxide, also known as lye and caustic soda, in order to assist in the extraction of alumina from bauxite.
QAL said "a failure occurred in the tank floor of one of the tanks which led to the shell parting from the floor."
This released the contents into the bunded area, causing a gaping hole to open up underneath the tank, which is capable of holding 10,000 cubic metres.
The investigation will determine the amount of material leaked into the ground, although QAL says this will take some time to complete.
Internal QAL experts are being supported by a specialist from Brisbane in the investigation.
QAL are also working with the newly-formed Department of Environment and Science on the matter.
Remediation works are under way to repair the damage to the infrastructure within the bund.
"Bunded areas are required around all storage facilities of this nature and act as containment areas in the event of a release," the QAL spokesperson said.
"The bunded area completed the task it was designed for. None of the material left the containment of QAL's South Trees Facility.
"QAL immediately activated a team to respond to the leak with our first priorities being people and the environment.
"There was no impact to people or the environment and the material has since been recovered and has not affected the production of the plant."
The December 5 event was the second sodium hydroxide incident involving QAL within the space of three months.
A caustic spill took place from a QAL vessel on September 25, resulting in Department of Environment and Heritage Protection officers completing water quality sampling at the Gladstone Harbour.
QAL has also been slapped with hundreds of thousands of dollars worth of fines for previous breaches.
The alumina refinery was fined $400,000 in the Gladstone Magistrates Court for a large-scale caustic leak in June 2015, and $125,000 due to a November 2012 incident where sodium hydroxide aerosol sprayed into the air for about an hour.
QAL said they have an extensive monitoring and maintenance program to ensure the integrity of our their refinery.