Tiwai Point aluminium smelter site contamination results 'might cause concern for people'
Friday, 15 October 2021
Rio Tinto says some of its Tiwai Point aluminium smelter site contamination results, as part of its closure preliminary study, might cause concern to people.
The company engaged GHD Limited, on behalf of New Zealand’s Aluminium Smelters, to complete a Detailed Site Investigation as part of studies to ensure the site was remediated to the required level upon its closure.
In July 2020, Rio Tinto announced it would wind down operations at the smelter, which employs more than 1000 people, by August 2021 because of high energy and transmission costs. However, after it reached an agreement on a new electricity agreement with Meridian Energy, operations were to continue until December 31, 2024.
Aluminium prices have nearly doubled since April last year to trade at a near-record high of $2943 (NZ$4247) a tonne, fuelling speculation that Rio Tinto will seek a new power deal to keep the smelter open beyond 2024.
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An investigation was conducted by GHD to assess existing information to identify areas of the site most likely to be contaminated and samples were collected of soil, groundwater, and drain sediment for laboratory analysis.
Rio Tinto aluminium closure readiness general manager Nicole Atherton said the report, release on Friday, is just one step in a phased process and more information would be released as it becomes available.
“We understand these results might cause concern for people and would encourage anyone with further questions to contact us at NZAS.enquiries@riotinto.com.”
Samples were gathered across 238 locations, mostly at levels 10cm and 1m below the surface and were assessed against a range of criteria as per the Ministry for the Environment Contaminated Land Management Guidelines based on potential future land use: industrial or recreational.
In total, GHD found 83 per cent of groundwater samples exceeded guidelines within the New Zealand Drinking Water Standards and Environment Southland groundwater rules.
Groundwater contaminant concentrations were highest in the central portion of the site and levels reduced with distance from this area, the report says.
The exceedances were primarily for aluminium and fluoride with a lower number of exceedances for arsenic, iron and pH.
About two-thirds of samples collected from on-site drainage exceeded guideline values and remediation was required in these areas.
Concrete barriers within the system prevented most of the sediment from discharging to coastal areas, the report says.
Soil samples showed 1 per cent of them did not meet the industrial land use guidelines and 9 per cent did not meet the recreational land use guidelines
The samples that exceeded guideline values were primarily from 10cm below ground level which indicated the contamination is close to the surface and can easily be remediated, the report says.
Substances that exceeded soil criteria were primarily aluminium, polycyclic aromatic hydrocarbons and fluoride with lesser exceedances of arsenic, vanadium, lead and total petroleum hydrocarbons.
Cyanide, asbestos and PFAS chemicals were not measured at concentrations in excess of criteria for an industrial or recreational land use.
All soil samples taken from outside the smelter’s footprint across the wider Tiwai Peninsula met the criteria for both industrial and recreational land use.
Given the site has been operating as a heavy industrial site for the last 50 years, exceedances of criteria were not unexpected, the report says.
Contamination within these areas would require management and remediation as part of the closure works, the extent of which will be dependent upon the remedial option chosen.
Atherton said it was committed to removing all Spent Cell Lining, managing waste and to remediating the site.
“We recognise some waste has been handled poorly in the past and this was not acceptable. We are working to significantly improve our performance.
“Given NZAS has been a heavy industrial site for more than 50 years, we expected that some areas would need remediation. This in depth analysis by GHD provides the critical information to do this work accurately and effectively, which includes addressing instances of contamination.”
The GHD report supplements the ongoing data collection activities by NZAS and highlights areas for further investigation.
NZAS has set aside $298m as a provision in its accounts for the closure and rehabilitation of its Tiwai Point site.