Thousands of kilograms of rubbish were washed out to sea in 2019, when an old landfill on the banks of the Fox River became exposed during flooding.
Volunteers pick up rubbish where a disused Fox River landfill spilled litter on the West Coast. Photo: RNZ / Katie Todd
Now, three years later, the remaining rubbish has been removed from the site - at a cost of over $3 million.
Managing old landfills is complex, but a volunteer believed it's better than the alternative.
Anne McDermott was one of the volunteers who helped with the clean up at Fox River.
"It was just devastating to see it - there was just rubbish everywhere," she said.
"90 percent of it would've been plastic... I certainly wouldn't want to see it happen again, I mean, the scale of the project was huge."
Hundreds of sites are thought to be at risk.
Dave Bull is a contaminated land specialist at the consultancy firm HAIL Environmental who says lots of rubbish dumps are on land particularly vulnerable to erosion.
He said: "New Zealand has a very dynamic coastal environment - beaches move, river mouths move - and that's always happened."
"And it will always keep happening. It's a very difficult thing to try and stop."
"The sea is a very powerful creature, rivers equally so, and sometimes you've got no choice but to get out of the way."
Climate change is making the problem worse, putting old landfills at greater risk of exposure.
The Canterbury Regional Council is taking steps to identify dangerous sites, using a new computer programme to analyse data.
Team leader of contaminated land and waste Graham Aveyard said until recently, consents for landfills didn't take climate change into account.
"Many of the consents didn't consider the risks from climate change and the vulnerability of landfills."
"But over this last weekend and over the last year, we've seen large flooding events..."
"And [the council] has devised a way to prioritise those [at risk] sites and find ways to protect them," he said.
The council has put its old sites into four categories: those threatened by coastal erosion; sea level rise; rivers flooding and river scour.
Simonne Eldrige, from environmental consultancy Tonkin and Taylor, said at risk landfills can be managed in a number of ways.
"In coastal situations, you might want to look at some form of coastal protection measures to create a barrier for the contaminated waste material."
"It might also be subject to flooding and in those sorts of circumstances, you might do some reprofiling of the surface or diversion of stormwater or interception drains," she explained.
All three experts agreed the best way to manage old sites is to completely remove the rubbish and put it in a new landfill.
The only catch is the price tag, with Aveyard noting complete removal and remediation is the most expensive option.
"Funding will be an issue."
"...who would fund the actual remediation of sites that are desperately needing protection?" he said.
"That will cost millions and millions and millions of dollars."
However, Anne McDermott said a clean up operation is also costly, and can be more difficult to co-ordinate.
"We were issued with hi-vis vests and gloves and someone was washing these every day so they were clean."
"We were provided with lunch, morning tea and then a night voucher - like someone was footing the bill for all of that..."
McDermott said "We only had to pay to transport ourselves to Fox [River] and home again ... but, y'know, the cost alone for the army that were there and their vehicles - it was just mind-blowing."
The country is using fewer landfills and as Simonne Eldrige explained, new ones are tightly regulated to reduce their impact on the environment and local communities.
"The modern, engineered landfill is millions of miles away from those uncontrolled fills and dumps of yesteryear, that we've seen with the likes of Fox River."
"The [new landfill] assessment generally looks at how you will contain the contaminants far into the future and site selection considers a number of risks, including natural hazards and climate change effects," she said.
Westland and Southland regional councils have started using Canterbury's computer programme to set up their own database of at risk sites.
Currently, there is no national data on vulnerable old landfills.