The Bluff aluminium smelter has revealed it has another 75,000 tonnes of highly toxic hazardous waste stored in buildings at Tiwai Point - and does not have a solution what to do with it yet.
The company says all 181,000 tonnes of the waste - another 106,000 tonnes is on a concrete pad close to the beach - is safe and secure.
However, documents show that the storage building floors have cracked in the past and contaminants have had to be pumped out.
They also show that this followed the storage pad cracking, causing "severe" pollution of groundwater with cyanide, but that it was leaking for years before the company cottoned on.
The cyanide plume - at levels underground thousands of times what it should be - lasted for at least 15 years, till 2006, during which time up to an estimated four to 12 kilograms of cyanide a day was being discharged into Foveaux Strait.
Studies concluded this leakage from the pad had no impact on marine life.
Other reports say the problem of the cracked shed floors did not contaminate the groundwater.
Officials told a select committee that the smelter company's legal liability to remediate the Tiwai Point site "has been difficult to pin down". The company has said it is planning to close down the plant "responsibly".
The public is hearing about the waste problems now due to an unprecedented focus by the media and the government on what state the smelter might leave the environment in if it closes, as planned, in four years' time.
The government has admitted it is "blind" on this and a $300,000 investigation is underway.
New Zealand Aluminium Smelters admitted last week to the full extent of its stockpile, at the same time as conceding that its options for getting rid of it were narrowing because exporting it was becoming more difficult.
However, it added in a statement to RNZ: "We are confident the waste material is securely and safely stored while we work on the best end user solution."
A visit from WorkSafe inspectors last week confirmed this, it said.
"While we work on a achieving a solution, NZAS remains confident that its practices regarding waste produced at its operation at Tiwai Point are robust and the waste stored in a way which ensures our community, the local environment and our employees are safe.".
WorkSafe said it was satisfied the waste was "stored and contained appropriately".
The cyanide that has leaked due to storage problems is in addition to the cyanide the smelter has permits to regularly discharge into the sea.
But it all comes from spent cell liner (SCL) waste. This is the most significant solid waste produced by smelters and contains cyanide, fluoride and ammonia - it can give off explosive gases if wet.
RNZ reported that 106,000 tonnes is stockpiled on a giant concrete pad 85m from the beach, next to DOC land.
Runoff from the stockpile is treated then discharged to the sea; it is allowed to contain "free" cyanide - the most toxic type - up 20 parts per million (20 grams per cubic metre). It has rarely gone above that and has in recent years been down at under 5ppm, according to NZAS records.
Fish can die at under 1ppm, but the sea dilutes the flow; the smelter is allowed to discharge up to three Olympic size pools of this effluent a year.
The SCL stockpile has been stuck at about 180,000 tonnes for a decade, despite the smelter exporting 58,000 tonnes since 2014.
"That is becoming increasingly difficult due to international laws around hazardous waste importation and shipping constraints," said the company, that is 80 percent owned by multinational Rio Tinto, which has access to SCL-processing plants overseas.
"As part of our detailed closure study NZAS is exploring other possible reuse options for SCL and welcomes input from any possible end users within New Zealand."
International industry guidelines say smelters should have long-term management plans for SCL waste that they disclose to the public.
RNZ has asked NZAS if it has a management plan for the waste - and to release it - similar to the management plans it has for its landfill. Plans for the landfill run to hundreds of pages and it must consult on with iwi and others.
Previously it said it would not provide operational details to the public.
The Invercargill City Council has chosen until now not to monitor activities permitted under its district plan - and waste storage is allowed in the smelter zone. A fortnight ago, the council said it would begin to do that across all industries.
The regional council Environment Southland, which regulates the SCL effluent discharge, said regional councils were not responsible for the storage of hazardous substances.
Secure storage compromised
Documents released under the OIA show the smelter's storage of SCL waste has been compromised at least three times; once, in the 1990s, from the huge concrete pad, that cracked; and from a storage shed or sheds on NZAS land, in 1995 and 2001-2005.
NZAS has not said if there have been more incidences.
The pad held SCL waste gathered since the 1970s. By the time the company detected it was leaking, in 1992, the pollution plume of cyanide, fluoride and ammonia was already 200 metres long and 14 metres thick in groundwater inching towards the beach.
Its epicentre was about 50m above the high tide mark.
"The discharge occurred without the knowledge of NZAS," consultants AquaFirma told Environment Southland in 1995.
The contamination was both "severe" in nature, but small in area at under one hectare, AquaFirma said.
Total cyanide concentrations were typically 800-1500 micrograms per litre but as high as 2400 mg/l.
This includes lethal "free" cyanide, and other less toxic cyanides. Ammonia averaged a high 1500 mg/l; and toxic fluoride around or under 1000mg/l.
Sixty metres offshore, in water 5m deep, cyanide at 60 mg/l was found 300mm below the seabed.
Micro-organisms can die at 5-10 mg/l, and fish at 0.2 mg/l, depending on the type of cyanide.
However, nature had come to the rescue at Tiwai Pt. The "free" cyanide in the leachate had been converted in the aquifer to 99-plus percent iron cyanides, or ferrocyanide, which are highly stable and low toxicity.
Ferrocyanide can convert back to free cyanides when exposed to sunlight.
So the smelter dropped its plan to pump the groundwater up and treat it, with the approval of Environment Southland, after an extensive investigation in 1995 by consultants Minenco found this might make things worse.
To make sure, the smelter began monitoring, at first every month at 17 wells.
Within two years, the council had cut that back to seven wells and quarterly.
In 2006 the council told the smelter it could stop monitoring altogether.
"There is no evidence that transport and discharge to the CMA [Coastal Marine Area] through groundwater is having any measurable impact on the environment," a 2005 NZAS report said in the run-up to this decision.
NZAS kept on monitoring off its own bat, and as recently as 2019 said the groundwater was OK.
More space - more problems
The cracked pad was replaced with a new one, on exactly the same spot 85m from the beach, in 1995.
Today that pad, the size of two football fields, holds 106,000 tonnes of SCL. It is sealed under a cover and with drainage designed to catch the leachate, which is then treated and discharged to the sea.
"It is extremely closely monitored, as is the coastal erosion on the peninsula," the company told RNZ.
But the smelter needed more space for the hazardous waste.
In 1992, the regional council had told the company that it did not need resource consent for a storage building "on the understanding that there will be no additional discharge of contaminants … from the building".
But three years later, a council memo marked 'confidential' said the cathode storage building floor had "cracked, with contamination present down to the second membrane".
"Thank goodness they overdesigned the building," it read.
Then, six years on, in 2001, they found more contaminated water under the floor.
It had "elevated concentrations of cyanide and fluoride" in it. Four years later, in 2005, it had been diluted, but was still being pumped out, the smelter's documents say.
NZAS told RNZ this showed the purpose-built foundations - of sand and impermeable membranes beneath a concrete floor - had contained the waste as designed.
"In short, the building did exactly what it was designed to do."
RNZ asked Environment Southland what it knew about the storage buildings.
"The conditions of the consent [to discharge effluent] do not require NZAS to report the amount of SCL that is stored at the site, so we are unable to comment on this," chief executive Rob Phillips said in a statement.
The Invercargill City Council said monitoring the storage was WorkSafe's responsibility.
Its responsibility was to ensure a company only stored as much hazardous waste as the District Plan allowed, group manager of Customer and Environment, Darren Edwards said in a statement.
But he did not say if NZAS had complied with this, or refer to the smelter when he added: "Our monitoring of the amount of any hazardous substance present, where this is a permitted activity under the District Plan, has previously been enforcement and complaints-based. As per our previous statement on this matter, we are seeking to implement proactive monitoring programmes in future."
RNZ has asked if the smelter was storing too much; and if the city council consented the construction or modification of the pads built in the 1970s and 1990s, or any of the SCL storage buildings.
What to do with the waste?
The toxic waste pile has kept steady at about 180,000 tonnes since 2010, even as smelting has generated more of it, by exporting some for disposal, mostly to Europe, where some industrial processes, such as cement-making, can reuse processed SCL.
Exporting was getting more difficult, but the smelter said it was looking to increase exports; it has held permits since 2014 for 78,000 tonnes, 20,000 more tonnes than it has actually exported to date.
Attempts to reuse SCL waste locally have foundered, and attempts to process that waste onshore have largely failed too, after a short-lived go of it by Holcim cement ended when its plant closed around 2015.
In the early 1990s, NZAS predicted it would generate 12,000-16,000 tonnes of SCL waste each year.
It spoke of setting up a plant to become one of few operators able to process the material, even as other smelters worldwide struggled to cope with it.
But by 1995, the pilot treatment plant "has problems and now has a lower priority", an Environment Southland memo said.
Today, the smelter was no longer talking about the processing, and is planning to close all its operations in 2024.
It said last year it would close in 2021, then delayed that by doing a deal over electricity pricing, and is now doing a "closure study" that will take several years to complete.
"Currently there are no cement manufacturers in New Zealand able to take the material so as part of our detailed closure study we are exploring other options and in particular would hope to find a local end user," NZAS said.
"We don't have all the answers right now but we are working hard to ensure we deliver the best result in the end. The best solutions can sometimes take time."
WorkSafe said it conducted an assessment visit at the smelter last week.
"Enforcement action can be taken should breaches be identified... No enforcement has been issued at this point."
It was waiting for some extra information "about processes for monitoring", but having to wait was normal.