The Government will have to pay millions of euro to clean up 250,000 tonnes of waste in 20 illegal dumps in Northern Ireland.
Large quantities of waste from the Republic has been found in illegal dumping sites in the North.
Minister for the Environment John Gormley says it is our responsibility under EU law to take back the waste for proper disposal.
Investigators from Northern Ireland's Environment Agency estimate that around a quarter of a million tonnes of waste from the Republic were illegally dumped at 20 sites between October 2002 and 2004.
An agreement has been reached between Dublin and Belfast, with EU approval, on how to finance both the clean-up of the sites and the proper disposal of the waste.
The Government will pay for the entire costs of disposal and 80% of the costs of taking the material out of the pits and remediating the sites.
The estimated bill for cleaning up two sites is €3m but the final bill could be tens of millions.
Environment ministers John Gormley and Sammy Wilson say that there is a high level of cross-border co-operation.
