An ammonium nitrate company in the Pilbara claims multiple releases of effluent from its plant on the Burrup Peninsula pose "no risk to people or the flora and fauna of the surrounding environment".
The Yara Pilbara Nitrates plant produces technical ammonium nitrate, an ingredient used for blasting in the mining industry.
The joint venture between operator Yara and Orica opened in August 2016.
In groundwater monitoring reports, Yara detailed several "unplanned releases" of process effluent containing ammonium and nitrate, which had occurred at the site.
The first release was reported to the Department of Water and Environmental Regulation (DWER) in March 2017, seven months after the plant opened, with further releases reported in July 2017 and September 2018.
In response, the company commissioned a "detailed ecological risk assessment", which concluded in late 2020 that the risk could be managed under a site management plan.
But the company had to change tack after heavy rainfall in May 2021 washed contaminated surface water into nearby King Bay.
In a report, recently published online as part of an application to the WA Government, Yara wrote this event resulted in a "potentially unacceptable risk and initiating the need for active remediation".
Late last year, as part of the first step of the remedial action plan, Yara said it removed almost 4,000 tonnes of highly concentrated nitrate soil within the boundaries of the facility.
The company recently submitted its application to the state government for the second phase of remediation, which aims to restore the groundwater condition onsite.
Yara hopes to complete these works this year, pending approval.
Construction problems to blame
The plant was originally touted as the "world's first modular ammonium nitrate plant", but problems early on could be to blame for the contamination.
"Throughout onsite monitoring, we discovered elevated nutrient levels in the groundwater at that time, which we've traced back to civil engineering and operational issues from the original construction of the plant and throughout the preliminary commissioning of the plant," Yara Pilbara's health, environment, safety and quality manager Ty Hibberd said.
"We've tackled the cause and have been working proactively with the regulator to develop the robust remediation plan."
Mr Hibberd was asked whether another heavy rainfall event could wash further contaminants into the bay but didn't directly answer the question.
Amount of contaminant 'unknown'
A spokesperson for DWER said the total volume of contaminants that entered King Bay after the May 2021 rain was unknown but noted there was an increase in nitrate concentration at nearby monitoring bores around the time.
Algal monitoring also indicated "short-term transient effects during the July–September period", the spokesperson said.
University of Western Australia Environmental Engineering programme chair professor Anas Ghadouani said nitrogen could have a destabilising impact on ecosystems when it got into waterways.
"Nitrogen are fertilisers. The reason that the environment is so reactive to these nutrients is that they are actually very rare, and then they are needed for primary production," Professor Ghadouani said.
"In environmental systems, there's always competition for nitrogen and phosphates.
"And when there is suddenly an increase in availability in natural systems, then organisms, usually primary producers like algae, will compete for these nutrients and that's why we have usually algal blooms, and we have eutrophication [water pollution]."
The spokesperson for DWER said no active remediation of King Bay had been needed after the rainfall event in May 2021 because of its "high flushing capacity".
"Modelling indicates a renewal of the total water body in under 1.5 days, [so] the ecological risk to King Bay is considered low," the spokesperson said.
But professor Ghadouani questioned that assertion, saying the reactive nature of nitrogen meant it could be absorbed very quickly.
"I appreciate the assumption is a high flushing rate will have less impact," Professor Ghadouani said.
"If you have reactive nutrients that react within minutes, in fact, some of the turnover rates for this element is actually within 30 minutes, then that's really not something that will hold scientifically, that assumption."
Monitoring and investigation ongoing
While no active remediation has been required outside of the boundaries of the site to date, DWER said this would be reviewed based on ongoing monitoring, investigation, and onsite actions.
"Extensive ongoing surface water, groundwater, sediment and algae monitoring, along with other investigations is being undertaken by Yara," the spokesperson said.
"Reporting on the current detailed ecological assessment is expected to be reported in the coming months."
