An eco-dilemma: The West Coast creek so acidic ‘you could dissolve a car in it’

Saturday, 15 June 2024

Mining company BT mining and its predecessor, Solid Energy, have spent tens of millions of dollars trying to clean up the West Coast's Ngākawau River.

**After a century of coal mining, the Ngākawau River on the West Coast was so polluted it was devoid of all aquatic life. Now, thanks to a multimillon-dollar clean-up, **the fish are returning. But one tributary is still toxic and a protected wetland stands in the way of fixing it. Joanne Naish reports.

From his front door, John Peterson has an idyllic view of the Ngākawau River. Peterson, a keen whitebaiter, has lived on the banks of the river north of Westport on the West Coast for 15 years. But he doesn’t fish there any more. “When you taste the water it's got a sort of funny taste,” he says. “It's definitely worse downstream from Mine Creek.”

The Ngākawau River wraps around the northern edge of the Stockton Plateau, home to the largest open cast coalmine in New Zealand. For years, the Stockton mine was run by state-owned Solid Energy and in that time the river could best be described as collateral damage.

Toxic runoff from the mine - known as acid and metalliferous drainage (AMD) - infiltrated the creeks and streams that fed it. Downstream from Stockton, the Ngākawau ran an ominous milky yellow, devoid of fish and almost all aquatic life.

The mouth of the Ngākawau River. Stockton mine’s coal handling facility is on the left and Ngākawau township on the right.

By the time Peterson moved in, Solid Energy had been ordered to clean up the Ngākawau, which it did until the company collapsed in 2015.

Stockton mine was sold to BT Mining ‒ a joint venture between Bathurst Resources and Talley’s ‒ two years later. As part of the sale, the Crown agreed to pay $77m for the ongoing clean-up of the catchment (It has spent $23m so far).

The clean-up was that rare thing in the complicated relationship between mining and the environment ‒ a success. It wasn’t perfect, but by 2015 whitebait had returned to the Ngākawau and a fish survey last year showed kōaro populations in the upper catchment had fully recovered.

Water quality was variable ‒ dissolved aluminium levels sometimes ran high ‒ but pH levels and turbidity were within consented thresholds. Overall, the Ngākawau was in vastly better shape than when a “cocktail of heavy metals” flowed through it in 2005.

One problem remains. Mine Creek. Just upstream from Peterson’s home is the last major tributary of the Ngākawau River yet to be treated. It runs, as its name suggests, direct from Stockton mine itself.

John Peterson lives on the bank of the Ngākawau River but chooses to fish the nearby Mokihinui River instead.

So acidic “you could dissolve a car in it”, as one BT manager put it. Soon after he moved in, Peterson filled a bucket with water from the creek and left it in his shed to evaporate. “I scratched the stuff off the bottom and it was coal,” he says.

Mine Creek flows into the Ngākawau River near its mouth. Upstream, the river is cleaner.

The solution is simple: install a sump like the two others already in place along the catchment to allow metals to settle at the bottom and the acidic water to be neutralised with lime before being redirected into the river system. At Mine Creek, however, this would come at the cost of a small piece of wetland, currently protected by national freshwater policy standards and all but untouchable.

Which leaves the government, the mining company and anyone who cares about the environment with an unenviable eco-dilemma: destroy a wetland or save a river?

The clean-up

Stockton Mine's Mangatini Sump has helped clean up the Ngākawau River.

The Stockton Plateau, about 35km north of Westport, sits 1100m above sea level. It is home to a spectacular and unique sub-alpine landscape and rare species such as Powelliphanta Augustus snails, the great spotted kiwi and the West Coast green gecko.

It also sits atop a rich seam of coal, part of the Brunner Coal Measures which, since the 1890s, have seen more than 200 million tonnes of rock disturbed and the surrounding aquatic ecology devastated by AMD.

At the Ngākawau, this led to a Parliamentary Commission of the Environment inquiry in 2004, which demanded remediation. Solid Energy built the first sump at Mangatini in 2009, capping the waste rock dumps and piping all the rainwater there. BT built a second sump at McCabe’s, near the St Patrick’s Stream tributary, in 2023.

BT Mining community and environment manager Barry Walker at Stockton Mine's Mangatini Sump. Walker says Mine Creek is still so acidic you could “dissolve a car in it”.

Mine Creek would be the third. BT is committed to building it but that would require amendments to the National Policy Statement for Freshwater Management 2020 and the National Environment Standards for Freshwater 2020.

“It all just got too hard,” says Barry Walker, BT’s mining and environment and community manager. “The approval process was so hard and so convoluted, even though I could demonstrate the beautiful [environmental] gain. Council, Treasury were all supportive. Iwi was totally supportive.”

Walker says the sump’s excavated rock would be rehabilitated with 2ha of wetland vegetation. Fish can already get up the Ngākawau River past Mine Creek due to the dilution effect of the upstream treated water from the Mangatini Stream and the untouched upper catchment, he says.

A Mine Creek sump would allow more species, including banded kokopu, to colonise or return to new areas of the river and move further up and down contributing waterways and ensure greater survival of whitebait.

Jon Harding, a freshwater ecology professor from the University of Canterbury, says the Ngākawau River’s water quality was now between pH5 and pH6 (The pH spectrum runs from 1-14 and is a logarithmic scale measuring the acidity or basicity of solutions. pH1 is the most acidic. Pure water has a pH of 7).

Harding helped lead a 2006 study which found acidity of pH2 and the “cocktail of heavy metals”. “Over the last probably 10 years or so, we've actually started to see whitebait coming into the lower part of the Ngākawau River in … reasonable numbers,” he says. “That's a really good sign.”

So could you eat the fish in the river?

“I think you’d have to eat a lot before you had any problems. You could swim in the Ngākawau. Personally, I wouldn’t.”

Walker says a third sump would improve the water quality enough to allow locals to use the river recreationally. “Children will be able to paddle and play in streams … [and enjoy activities] such as kayaking and the exciting white-water opportunities on the Ngākawau River.

“People will be able to fish for whitebait, and collect mahinga kai. Local communities will feel they are able to appropriately welcome and feed visitors from their own food baskets, increasing the mana of the area.”

West Coast Regional Council chief executive Darryl Lew said the Ngākawau’s rehabilitation has been a “big success”. BT provided monthly environmental reports of the river’s pH levels, turbidity, flow and thallium content as well as annual fish surveys.

“We meet with them regularly about their results. It’s remarkable how they manage AMD coming off that site…[it’s] almost world class.

“We're very, very happy with the rehab that's going on there.”

The flipside

Ngākawau translates as ‘home of the shag’, so named for the colonies of the bird that used to live on the river. Today, the colonies are gone. One of several signs the river is yet to be restored to its full pre-mining ecology.

Resources Minister and unabashed mining proponent Shane Jones at Macraes mine in Otago.

Forest & Bird regional conservation manager Scott Burnett says the latest fish survey showed there still was not the full complement of fish species that might normally be found in an unmodified river.

About 1.1m tonnes of coal is exported from the Stockton coal mine for steel making.

More mining was not the way forward. “Forest & Bird is not anti-mining per se,” he says. “We are anti-mining on conservation land, we are anti-coal mining for climate reasons and any mining that endangers biodiversity.”

Bathurst Resources (the mining half of BT Mining) has been in trouble in Canterbury in recent years for exceeding resource consent conditions and “thrashing a wetland” with mine drainage issues. The Government only receives $9.5m a year from mining royalties, Burnett says. The risk, and the damage, isn’t worth it.

“Stack that up against what they've spent on cleaning up AMD issues at Stockton and it doesn't make sense. Mining creates short term jobs and the majority of the profits accrued go to overseas shareholders and New Zealand taxpayers are left with the clean-up costs.”

Stockton plateau is special, Burnett says, and its rare wetland should not be destroyed, even for the Mine Creek sump that would help the river.

The endangered native fish species kōaro have fully recovered in the Ngākawau River.

“It's totally a dilemma and paradigmatic of mining in this fragile environment. You have to destroy a wetland to save it. It’s crazy. Don't screw up any more of the environment.’’

The new Government might be about to test Burnett’s rationale. Resources Minister Shane Jones declared in his first speech in Parliament that “mining is coming back”, while National Policy Statements for biodiversity and freshwater were “out the back door”.

The mining industry was a key contributor to New Zealand’s export earnings, Jones said. In May, he announced the Government’s Draft Minerals Strategy for New Zealand to 2040, which aims to double the value of New Zealand’s mineral exports to $2 billion by 2035 (Bathurst holds permits over more than 10,000ha in the Buller coalfield, employs 305 people and contributes to one-fifth of the overall GDP for the district. It exports 1.1 million tonnes of coal for steelmaking and the manufacture of products such as solar panels and carbon fibre components).

Unsurprisingly, Jones was full of praise for BT Mining’s clean-up job at the Ngākawau River. Regulation preventing Mine Creek being restored because of a small piece of wetland was “nonsensical”.

BT mining’s coal loading rail facility at the mouth of the Ngākawau River.

“Some ecophile holding a pen clutching their pearls is stopping common sense,” he tells The Press. “Some unknown ecological apostle is undermining better environmental outcomes.”

Jones has also announced changes to the Resource Management Act to remove “burdensome red tape” for the coal mining industry and is one of three ministers with final say on consenting infrastructure, mines, roads and housing projects under the controversial new Fast-track Approvals Bill.

Critics of the bill are “economic Luddite green burgers”, Jones says. “If we have our way and Fast Track passes into legislation those green burgers will be goneburgers.”

Environmentalist Frida Inta is still concerned about the quality of the Ngākawau River.

“Kiwis have a good dose of common sense and can see a balanced approach can generate a better quality of life in New Zealand.”

Bathurst Resources chief executive Richard Tacon has submitted on the fast-track bill. He said he was committed to upholding environmental standards but the current rules were complex, open-ended and costly.

The company spent tens of millions of dollars for approvals for its Escarpment mine at Denniston near Westport which it mothballed in 2016. It went through 12 appeals.

Tacon hoped to use the fast-track legislation to apply for the next stages of the Stockton mine and Rotowaro mine in Waikato as well as renew some authorisations for existing operations.

Bathurst also wants to build a 5km haul road through Department of Conservation land to bring coal from the Denniston plateau to Stockton where it could be railed to Lyttelton.

Much of the West Coast establishment agrees with the reform plan. A forum of the region’s mayors, chairs and iwi said the new draft minerals strategy aligned with the aspirations of its communities and was “a comprehensive plan to secure and increase mineral supply, enhance economic opportunities, and support environmental sustainability”.

Te Rūnanga o Ngāti Waewae representative Francois Tumahai went further: “We support the Government’s efforts to involve iwi in the development and management of natural resources, ensuring that our cultural values and environmental responsibilities are upheld.”

A bullish Jones and a pro-mining government might end the Ngākawau’s dilemma, then. But that isn’t the same as solving it. Environmentalist and West Coast resident Frida Inta says the river is better than it was, but BT could do more to keep it clean.

“It's opaque and has a really terrible rust colour. The rocks are all brown along the edges,” she says.

Mine Creek, in particular, remains disgusting.

“You wouldn't fish or swim there. I don't think the fish would want to go up this river because [of] the turbidity for one thing. It's just terrible.”

Inta has no problem with mining but worries about the river and the environment and the cost of remediation falling to taxpayers. Plus, an end to the Ngākawau dilemma would only direct attention back to a bigger one:

“[Mining] provides jobs for the community [and] assets to the community, which are really two positives.

“But, on the other hand the sub-alpine ecology is really special. It's very beautiful up there.”