Investigations are under way to see if cancer-causing chemicals left behind by the laundering of diesel have got into south Armagh's water supply.
The laundering plant was found just a field away from Armagh near Castleblayney, Co Monaghan when it was raided by customs officers and armed gardai yesterday morning.
Senior customs officers and council environmental staff were taken aback to find some of the highly toxic residue, left by the laundering process, was being piped into purpose dug ditches in adjoining fields.
The chemicals are toxic to humans and animals and carcinogenic. Concerns were also raised about the welfare of nearby horses and rabbits.
Officers seized 37,000 litres of laundered fuel, 200 bags of bleaching agent, two tankers and a van.
Three skips of toxic waste were also found. Other equipment was dismantled and taken away for examination.
The plant had the capacity to launder an estimated 20 million litres of fuel a year.
Senior customs officers and council environmental staff were taken aback to find that some of the highly toxic residue left by the laundering process was being piped into purpose-dug ditches in adjoining fields.
"This is the worst I have seen," said Kieran Duffy, senior executive engineer with Monaghan County Council.
"There is total disregard for the environment; as you can see they built a purpose drain beside the facility to take the run-off from the site.
"It is crazy -- we are not far from the local water supply source for south Armagh, the Lough Ross scheme.
"If it got into a stream it would kill fish and plant life," Mr Duffy added.
The concern was echoed by Sean Kelleher, assistant principal officer in charge of customs enforcement along the Border.
"The waste is allowed to percolate into the earth. It is horrendous what I am looking at here. I can't believe people are doing this to the environment," he said.
The raid by customs and gardai was the culmination of a specific operation to tackle organised crime in the border area.
"We hope the message is getting out that we are paying significant attention to this type of criminality," said a garda spokesman.
The diesel laundering was taking place in tanks concealed inside 40ft trailers.
A man in his 40s was arrested in relation to the discovery.