Police and customs officials today seized 17,000 litres of laundered diesel in a raid on an illegal operation at farm buildings in the Camlough area of Co Armagh.
Two vehicles adapted with concealed tanks for transporting fuel were also seized along with pumping and storage equipment.
The plant had the capacity to process 40,000 litres of diesel per week.
HM Revenue & Customs said such operations cause serious damage to the environment. John Spence, HMRC Anti-smuggling manager Northern Ireland, said:
"The laundering plant was discovered at a rural location not far from a local beauty spot where acid waste has been dumped in the recent past and recovered at great expense.
"People need to be aware of the environmental and safety issues surrounding laundering plants and vehicles adapted for transporting fuel.
"They need to consider what happens to the waste by-product and the damage caused by contamination to arable land and our water and rivers."
Four tonnes of highly toxic acid waste were removed from the site during the operation. A HMRC spokesman said no arrests have been made but inquiries into the operation are continuing.
PA