The Department of the Environment began investigating the site run by Neil Rooney of Ballytustan Road, Downpatrick, last year.
They found that Mr Rooney had dumped large volumes of domestic and commercial waste, as well as agricultural slurry.
Both the slurry and contaminated leachate were running freely off the landfill and "seriously polluting" nearby streams.
Further investigations revealed that some of the waste had come from the Republic of Ireland.
The DoE’s environment agency, the Environment and Heritage Service, is calling for 70 more staff to help it deal with the problem and also for extra powers to allow it to arrest lorry drivers found to be illegally carrying waste.
In early January, Downpatrick magistrates found Mr Rooney guilty of both causing polluting matter to enter controlled waters and of illegally dumping waste.
He was fined £10,000 for the first charge and £12,000 for the second. The £22,000 total fine was Northern Ireland’s highest ever for an environmental offence.
Mr Rooney did not attend the hearing and was not legally represented.
The DoE could not answer how the waste would be removed from Mr Rooney’s land.