Waste plan at UK’s largest opencast mine Ffos-y-Fran ‘dangerous’

Concerns have been raised about the safety of three large dumps planned to remain above Merthyr Tydfil after the closure of the UK's last open coal mine.

A geotechnical report prepared for the council warns of a “significant risk of slope instability” at Ffos-y-Fran, while campaigners say plans to keep the peaks in place are “staggering”.

Emails obtained by the BBC show the Welsh Government is considering stepping in to take control of the final planning decision.

Mining company Merthyr South Wales Ltd (MSW) said the suggestion that “purpose-built, engineered structures” pose the same risks as historic coal deposits is “incorrect and misleading”.

Two years since the cessation of production in Ffos-i-FranThere remains significant uncertainty regarding the future of the controversial project.

Having received permission back in 2005, the UK's largest quarry was officially classified as a “land reclamation scheme”.

This meant that part of the profits made from the sale of 11 million tons of coal over 15 years had to be used to clean up the area, riddled with the remains of old industries, and return it to a green hillside for the community.

“It was supposed to be for the public good, they were going to restore all rights of way and agricultural use,” said Chris Austin, who lives nearby.

He now fears the community will be left with “dangerous voids, dangerous councils and areas we can't use”.

“It’s very concerning,” agreed Alison Austin, Chris’ wife.

“We were forced to accept this open-pit coal mine… we now find ourselves in a much worse situation than when we started.”

The current developers – MSW – have sparked local anger and lawsuits after I continue to mine and sell coal more than a year has passed since the expiration of the building permit.

They have since unveiled a new – and much cheaper – recovery plan, warning of a “lack of funds” available to deliver what was previously agreed.

According to the original proposals, large spoil heaps accumulated over many years would be used to fill the main mountain space, 175 meters (574 ft) deep.

The dumps, known as overburden mounds, contain 37 million cubic meters of material removed over the course of the quarry's operation.

Now the company wants to reduce the height of one tip while leaving the other two in place.

He describes them as long-term stable structures and says the void in the mining industry will itself become “natural lake“.

The application is being reviewed by Merthyr Tydfil Council planners, who have commissioned a geotechnical report from engineering firm WSP.

That document concluded that the arrowheads were constructed as “temporary earthworks” and the proposals “do not provide confidence that the arrowheads and slopes will remain stable and will not pose an ongoing risk to the residents of Merthyr Tydfil and a potential financial burden.” [to the council]”.

The impact of climate change “appears to have been overlooked” – although in some cases it is “dismissed without any supporting evidence”, consultants warn.

They also note that one of the points, known as OB1, rising some 170 meters above the main road along Ffos-y-Fran, has already been damaged by a landslide in 2022.

The report also noted “a recent history of a number of tip failures in south Wales as a result of heavy rainfall”.

Delyth Jewell, Plaid Cymru's climate spokesperson, warned Merthyr Tydfil residents they would have to live with a “botched restoration” and said leaving the finials in place would be “stunning” and “unconscionable”.

“Carbon tip slippage is not a theoretical risk,” she said.

The Welsh Government recently announced a new Wales Brownfields Authorityformed due to concerns about the country's coal reserves, and is headquartered in Merthyr Tydfil.

Hough Elgar, director of Friends of the Earth Cymru, warned he may now need to add the Ffos-y-Fran overburden mounds to the list of sites to monitor.

“This is an additional burden on public authorities and is completely unacceptable,” she said.

In a letter to the council, consultants on behalf of MSW said they had “serious concerns” about the geotechnical report, which they described as a “desk assessment”.

In response, they commissioned their own analysis from geological and mining consulting firm James Associates, refuting WSP's findings regarding the stability of the tips.

It states that the overburden embankments were constructed to an approved design in accordance with regulations and were supervised by a specialist.

The landslide at OB1 was the result of excavation work and the likelihood of a future collapse could be “absolutely minimized” by appropriate engineering work, it said.

The reference to recent landslides at old coal mines in South Wales was “a case of comparing 'apples and pears'”, mine consultants added.

Typically, the tops of the collieries were located on steep hillsides, while the Ffos-y-Fran overburden embankments are located “on land with gentle slopes”, with differences also being in how they were built and the drainage systems they used, they say.

The company also claims its new offerings are more sustainable, reducing carbon emissions and air pollution from the heavy machinery needed to repurpose land while creating a “more interesting and naturally biodiverse landscape.”

Estimates of how much it would cost to remove the tips and fill the voids vary, ranging from £50 million to £175 million.

“The company's latest published accounts… (March 2025) include provision of approximately £91.2 million to meet the requirements of the approved recovery scheme,” the council noted in a recent letter to the firm.

But it now “appears to be relying” on using funds from a £15 million account set up with the council as a backup should the firm fail.

Mine consultants respond that detailed cost estimates are “currently being prepared.”

Last year the Senedd environment committee described the oversight of the Ffos-y-Fran coal mine as “a case of epic mismanagement“, which now threatened to leave a “permanent scar” on Merthyr Tydfil.

Campaigners have called on the Welsh Government to take over the decision-making process.

But in the emails, officials noted “the potential consequences of such actions, including the risk of site closure.”

They wrote to the council in August asking for more information.

“Given the level of risk… we are mindful of the need to ensure that a robust evidence base is provided to Welsh Ministers to justify any options they may wish to implement,” the email said.

Ms Jewell, the Senedd member for South East Wales, said the Welsh Government had a “moral obligation to ensure the safety of the people of Merthyr Tydfil” and should intervene.

In a statement, Merthyr South Wales Ltd said it was “particularly disappointed” by Ms Jewell's comments, which they said risked “undermining confidence in the planning system by creating political pressure on what should remain an evidence-based determination”.

“Merthyr South Wales Ltd remains fully committed to co-operating with the planning authority and has every confidence that the decision on the application will be lawful, impartial and based on professionally reviewed facts, records and advice,” it said.

The council said it would undertake further consultation once it receives more information from the developer.

The Welsh Government said it was working with the council and other partners “to ensure the best outcome for local people” and said the case remained “under active consideration for challenge by Welsh Ministers”.