Tiwai Point aluminium smelter clean-up costs could reach a billion dollars after a report review confirmed significant historic and ongoing contamination of the site. 

Environment Southland (ES) today released the findings of its review of a report commissioned by smelter operator New Zealand Aluminium Smelters (NZAS). 

It found "significant contamination of the site", including surface soil, groundwater and stormwater drains, with fluoride, aluminium, arsenic, hydrocarbons, heavy metals and cyanide. 

ES now wants more information from NZAS, owned by mining giant Rio Tinto, to assess the impact of the contamination on the surrounding environment. 

"With any industrial operation of this scale, some level of contamination at the site is to be expected, however, it is evident from the data supplied by NZAS that a significant mass of contamination has been discharged into the environment," ES chief executive, Wilma Falconer, says.

"What this data doesn't tell us is whether the historic and current NZAS operations have had, or are causing, negative effects to the land, groundwater and coastal marine environments."

Falconer says the NZAS report provided a "preliminary snapshot" of the site, environment and some detail on contamination levels. 

But a lot of data necessary for a full assessment was missing, including data relating to the landfill, spent cell liner pad and wider environment.

Falconer: "The gaps in the data mean we are yet to understand the full extent of contamination at the Tiwai site and the impact on the surrounding environment, including the coastal marine area." 

ES commissioned EHS Support, a consultancy with international experience in decommissioning smelters, to assess the NZAS-commissioned 'Detailed Site Investigation' report. 

EHS' Simon Hunt says the contamination at Tiwai Point, near Bluff, is similar to other smelter sites, with contamination occurring as raw materials arrived on site, as they were processed and during air discharges. 

"These contaminants kind of build up within the site, within the soil, depending upon the kind of chemical characteristics of those particular contaminants, then some will leach more readily into the environment," he says.

Hunt says the potential impact on human health is not yet known, and assessing that is part of the ongoing work.

Rio Tinto has estimated it will cost more than $700m to clean up the site when the smelter closes down, excluding the landfill there.

Falconer says: "I think between that and potentially a billion dollars to clean up that site was a reasonable estimate". 

NZAS chief executive Chris Blenkiron says it has been working closely with ES since receiving the report in 2021. 

"We recognise some waste has been handled poorly in the past and this was not acceptable," Blenkiron says.

"Significant work is already underway to remove waste and improve our environmental performance while we continue to enhance our monitoring regime. 

"We will remediate the site whether we operate beyond 2024 or not." 

He says some practices, such as wet washing of reduction cells and superstructures, are being stopped to reduce the level of contaminants in water discharged from site.

NZAS has stopped depositing any waste into the on-site landfill and shipments of Spent Cell Lining have been exported to be recycled for alternative use.

ES has now set out a programme of work with NZAS to extract more information about contamination, including drilling more bore holes and monitoring wells, more tests, monitoring and data releases. 

That is six to 12 months of work. 

"We continue to see a positive pathway for a future beyond 2024 and are working closely with Ngāi Tahu, Environment Southland, and the Southland community on long term outcomes for the site," Blenkiron says.