A diesel-laundering plant which is estimated to have cost the Government €1 million a year in loss excise duty has been raided.
Officers from the Revenue's Customs service seized 10,000 litres of diesel, equipment and a vehicle near Emyvale, Co Monaghan, on Monday night.
The illicit facility had the capacity to launder 8,000 litres a day with a potential loss of revenue of €1 million a year.
Two people were questioned at the plant, and a file is being prepared for the Director of Public Prosecutions, the Revenue Commissioners said.
Customs, gardaí and Revenue officials from Dublin and Dundalk began the raid on a farm at around 10.30pm on Monday. They discovered the illegal diesel wash, and spent until 6am on Tuesday searching the area and dismantling equipment.
It is estimated that the plant may have been in operation for up to a year.
Officials from Monaghan County Council's environmental department were examining a large quantity of toxic waste which came from the removal of dye from the diesel.
At a recent meeting of Monaghan County Council, director of environmental services Gerry Kelly warned the council that the Department of Finance was querying the amount the council was spending in cleaning up after illegal plants were discovered.
Mr Kelly told the meeting that "the cost of the clearing up of the toxic waste was €750,000 in the last two years alone, and now the Department of Finance is putting pressure on the Department the Environment to see if that money is being well spent, and querying why so much waste is appearing in Co Monaghan".
When the councils pay for the clean up of toxic waste, the cost is usually refunded to them by the Department of the Environment.
Mr Kelly warned: "Monaghan County Council must take action; we cannot afford to leave this material on site, it can cause an environmental catastrophe and €750,000 may be small money at the end of the day if we left that material on site."
In the last year alone the amount spent on cleaning up the sludge cost some €40 to €50 per house in the county.
Mr Kelly said: "We can't expect the householders in Monaghan to pick up that tab; we can't do this on our own, all we are doing is dealing with the problem as it arises; we are getting new finds every week."
Some people knew the people involved. "We have to get them to feed information to the council so that we can identify the people who are involved in it."