One of the country’s largest oil laundering plants has been put out of business.
The black market operation, which was able to process 20 million litres of fuel a year, was discovered in a scrapyard in Co Monaghan, about 100 yards from the border.
A local man in his 40s has been arrested.
The plant in Drumacon, near Castleblayney, was raided after a lengthy investigation.
Customs said it had the capacity to launder about 40,000 litres at a time and would have cost the Exchequer €11m a year in lost duty.
Officers seized 37,000 litres of laundered fuel, about 200 bags of bleaching agent, two tankers and a van.
Two tanks in the scrapyard could each hold about 20,000 litres of green diesel which was bleached before being siphoned off into oil tankers.
Three skips full of toxic waste were also discovered and ancillary equipment used in the illegal operation was dismantled and seized.
The raid was carried out by officers from Revenue’s Customs Service, assisted by gardai from the Northern Regional Support Unit and local uniformed officers.
The arrested man was being held at Castleblaney garda station.