Ouvea premix cannot be stored at Tiwai Point, says smelter boss

Aluminium manufacturer Rio Tinto does not own a hazardous substance being stored in Southland warehouses but the company remains committed to its removal, according to the boss of the the Tiwai Point smelter.

New Zealand Aluminium Smelters (NZAS) chief executive Stewart Hamilton was responding to a letter from Environment Minister David Parker in which Parker said he was considering legal action against NZAS over its failure to deal with its hazardous waste.

NZAS is majority owned by a subsidiary of Rio Tinto.

The substance, ouvea premix, gives off ammonia gas when wet. In February, the Mataura building housing it was threatened by floodwaters.

When Rio Tinto subsequently pulled out of a deal to fast-track removal of the premix, Parker wrote a scathing letter to the aluminium producer, urging it to take responsibility for the class-6 hazardous substance.

Hamilton’s letter of response was released to Stuff under the Official Information Act.

In the letter, Hamilton said the company ‘‘remains committed towards working towards a sustainable solution for Southland and the people of Mataura, and that the ouvea premix is removed as soon as possible’’.

NZAS was not able to temporarily store the ouvea premix at its Tiwai Point site, the letter said.

This was because any potential facilities would require significant remediation, which would cause significant delays, additional significant costs, and related legal issues, it said.

NZAS had provided suggestions of more appropriate storage sites.

The company was also unable to stop processing aluminium dross in order to process ouvea premix instead because they were two different materials and the premix needed to be treated differently, Hamilton wrote.

The company had suggested other potential users of the premix, such as cement manufacturers, he wrote.

About 25,000 tonnes of ouvea premix was left in five Southland warehouses, including the former paper mill building at Mataura, when Taha Asia Pacific went into receivership in 2016.

In the letter, Hamilton addressed the company’s business relationship with Taha, saying it only became aware of ‘‘significant compliance issues’’ relating to the handling of the ouvea premix material towards the end of its five-year contract.