Gardai and customs officers have uncovered an an oil laundering plant in Drumacon, Co Monaghan following an intelligence-led surveillance operation.
The plant had the ability to launder over 15 million litres of fuel per annum with a potential loss to the exchequer of over €8m.
A forklift, six vehicles and ancillary equipment were also seized.
In addition, seven tonnes of toxic waste - the by-product of the laundering process - were also seized.
In a connected search of a commercial yard in Longfield, a tanker with 20,000 litres of fuel, a trailer with a concealed tank and 68 bags of bleaching earth were also found.
One man in his mid 30s was arrested earlier this morning and is currently being detained at Carrickmacross Garda Station under Section 4 of the Criminal Justice Act.