In many ways the village of Groesfaen, near Pontyclun, is typical of a lot of villages just outside Cardiff.

Large, detached houses with unimpeded views across greenbelt land will regularly cost at least £500,000 here, with the bigger ones obviously going for more. It’s not a suburb of Cardiff, but it feels like it could be a suburb of the Vale of Glamorgan or Monmouthshire.

With that in mind, it's extraordinary that between 1965 and 1972 the disused Brofiscin quarry in the north of the village was used to dump deadly chemicals produced by Monsanto in their Newport  factory.

The quarry was filled and its history forgotten by many until 2003 when it started to leak and smells drifted across the village.

A subsequent report from the Environment Agency in 2005 revealed that the site was one of the most polluted in Britain. It was revealed that at least 67 toxic chemicals - including Agent Orange derivatives and seven different PCBs - were leaking into the porous ground at the former limestone quarry.

What are PCBs?

PCBs, or polychlorinated biphenyls, are highly carcinogenic chemicals that were used widely in consumer products like paints and as heat transfer fluids in industrial settings. 

Their dangerous properties were confirmed by the 1960s and their use decreased before being outlawed completely by most countries during the 70s.

In 1968, PCBs contaminated the food chain in Japan leading to more than 500 deaths and a national scandal.

By 2011 - eight years after the smell of sick engulfed Groesfaen - a new waterproof cap was laid over the entire Brofiscin site at an estimated cost of £2 million.

This was meant to contain the toxic chemicals and protect them from contact with rainwater, condemning the barrels inside to rot for eternity.

For years, Monsanto refused to contribute to the clean up cost because they had hired a third party waste disposal company to dump the chemicals, and denied any responsibility.

An agreement was eventually reached where they agreed to contribute towards the cleanup costs, along with BP (who were responsible for a small part of the dumping at the site), and Veolia (who eventually acquired the company who dumped the chemicals at this makeshift landfill site).

The National Wales: The Brofiscin quarry site today. Japanese Knotweed has been identified on the site (Image: Onthemarket).The Brofiscin quarry site today. Japanese Knotweed has been identified on the site (Image: Onthemarket). It should be bad enough that one of these sites exists in the entire world, let alone in the same area of Wales. However, some five miles further north, Monsanto dumped even more chemicals during this time at Maendy quarry - another defunct site on the hills above Church Village and Treforest, due west from Hawthorn. 

One of the nearby mountain streams that runs down into the Afon Taf has an ancient name that has become tragically prescient - Nant y Dall, which means 'The Stream of the Blind'.

Internal documents from the time - which surfaced during litigation decades later -  show the corporate panic at Monsanto as they created a 'Pollution Abatement Plan' to try to mitigate the effects of the incoming ecological disaster on their bottom line.

One of the options in the report suggested they did nothing. 

Thankfully, they decided to reveal the environmental harm of PCBs, although they would now control the narrative around how much information was known and when it was known.

The National Wales: Pontcysyllte Aqueduct Pontcysyllte Aqueduct

Elsewhere, the historic Pontcysyllte aqueduct which crosses the River Dee near Ruabon, south of Wrexham, is visited by thousands each year, and is seen as an emblem of the area’s industrial past.

If you were to visit as part of a coach party, your bus would be parked a short walk from the iconic canal bridge on tarmac that used to be the car park for the adjacent Monsanto plant which was demolished in 2009.

Waste from this plant was not exclusively buried in landfill - a more novel approach was also taken by the local authority instead, in the form of what’s become known as an “acid tar lagoon”.

The National Wales: The acid tar lagoon at Llwyneinion sits ominously above schools and houses in the village of Rhosllanerchrugog near Wrexham (Image: Google).The acid tar lagoon at Llwyneinion sits ominously above schools and houses in the village of Rhosllanerchrugog near Wrexham (Image: Google).

Leaving the nearby village of Rhosllanerchrugog on a country lane going north you’d be forgiven for thinking the trees and fences around you were anything but ordinary. However a sign on a green palisade fence reveals the truth: “DANGER. FORMER WASTE TIP. ENTRY PROHIBITED”.

The acid tar lagoon is an artificial lake filled with acid, which supposedly breaks down any harmful chemicals that are poured into it. More than 1,000 drums of harmful waste were dumped here over the years.

The fence was only erected after complaints from locals in 2006.

This acid lagoon caught fire in 1980 - its effects being felt up to 20 miles away - although authorities have claimed that it no longer poses a public health risk. 

Locals are still concerned about continuing potential contamination that could be caused by wildlife like ducks who have been seen in the lagoon before flying off elsewhere.


The Llwyneinion tar pit is only a few hundred yards away from a primary school and dozens of homes. A survey in 2011 revealed that it would take four years to clear the site, at a rate of removal of 120-150 tonnes of toxic waste a day.

A freedom of information request last year revealed that another acid tar lagoon exists in the neighbouring county of Flintshire, although the council has yet to confirm its exact location to The National.

Environmental authorities argue there’s no longer a danger to public health from any of these sites, although freedom of information requests in the past have revealed that PCBs are still being discharged into the Severn estuary from the former Monsanto site in Newport - which is still a chemical factory to this day, although it’s now owned and operated by Solutia.

The National will be investigating these sites in depth over the coming weeks. 

You can read the second part of our investigation here

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