Around 8,000 litres of toxic diesel sludge was discovered this morning near Castleblayney.
The diesel was discovered near Mullyash, outside Castleblayney.
Officials uncovered eight containers of the substance, which is a by-product of the illegal removal of dye from agricultural diesel.
Six of the containers were found in the middle of the road at Knocknaneen, near Mullyash Community Centre, while the remaining two were discovered off the Newtownhamilton road.
This is the 17th incident so far in 2012, costing the Council over 300,000 euro overall this year.