A man was arrested following the discovery of a diesel laundering plant and 60,000 litres of toxic waste at an oils storage yard in the Newtownhamilton area of Co Armagh.
The operation had the capacity to produce up to 8m litres of illicit fuel a year.
The premises was raided by the PSNI and the UK's Revenue and Customs.
Some 19,000 litres of laundered fuel, four filtration units and a vehicle were seized in the operation, according to a statement from UK Revenue and Customs.
UK's Revenue and Customs' Mike Connolly said 'any fuel laundering is unregulated and dangerous but the volume of waste on this site is staggering.
'The by-products from the laundering process can cause severe damage to the environment with taxpayers and local ratepayers having to pay for the clean-up costs'.
The man arrested in the operation has been released on bail pending further inquiries.
