A report commissioned by New Zealand Aluminium Smelters (NZAS) has found "numerous legacy and ongoing sources of contamination to the environment" at its Tiwai site.
Last year, Environment Southland engaged in a programme to identify the amount of contamination at Tiwai Point and the potential effects of pollutants at the site.
It engaged EHS Support, a consultancy with international experience in decommissioning smelters, to review the findings.
It found a number of chemicals have been discharged into the environment including groundwater, soil and coastal marine areas.
"Over time a significant mass contamination has been released into the environment, however there are gaps in the data and we're yet to understand the full extent of the contamination on the site" says Environment Southland Chief Executive Wilma Falconer.
The data reveals a range of pollutants across the site including fluoride recorded at 8-16% concentration in surface soil in some areas.
Groundwater is also contaminated with elevated levels of fluoride, aluminium, arsenic, PAHs (hydrocarbons) and cyanide.
"We understand that some of the contaminant concentrations are above various risk criteria at the site's surface and they do require further investigation" says Falconer.
EHS Support Consultant Simon Hunt says action is now underway to address the contamination and ensure it's well managed.
"There needs to be work done both within the inner harbour and Foveaux Strait to actually understand the effects where this contamination is actually discharging"
"There's a whole programme of work that's being planned that's being discussed with Environment Southland and that information's being shared with NZAS" Hunt says.
Assessment will begin in contaminated areas to understand what the concentrations are, which will determine whether it does pose a risk to the surrounding environment.
Environment Southland says it's working with NZAS on an enhanced monitoring programme.
"They've got an extensive network of wells on the peninsula and they have now lodged with us a consent to drill an additional 45 bores to help us identify more information on the site"
"We've also asked them to drill a further 7 monitoring wells in the areas that we're interested in" says Falconer.
Environment Southland is also asking for current and historic data monitoring information held by NZAS that shows levels of contamination over time on land, in groundwater and in the coastal marine area.
"We are now clearer about the actions we need to take to understand the extent of the contamination at the site and to ensure historic and on-going production waste is well managed, before and when the smelter closes" says Falconer.
EHS Support says it's still 6-12 months away from understanding what the potential risks are.
NZAS has estimated it'll cost around $700 million to clean up the site when the smelter enters the remediation phase.
But Environment Southland expects it'll be more.
"The remediation plan that New Zealand Aluminium Smelters has released in its preliminary closure study, they put a dollar figure on that, their dollar figure is probably a reasonable assessment of cost excluding the cost of cleaning up their landfill area so they were talking something in the vicinity of $700m dollars"
"I think between that and potentially a billion dollars to clean that site up is a reasonable estimate" Falconer says.
The smelter will remain open until at least the end of 2024, after mining giant Rio Tinto reached a new electricity agreement with Meridian Energy.
It was initially set to close in August 2021 because of high energy and transmission costs.
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