A Garda investigation into the suspected illegal dumping of household and construction waste at Tymoole, Rathfeigh, Co Meath, began yesterday with gardaí sealing off the area.
The Environmental Protection Agency (EPA) and Meath County Council are also involved in the investigation.
The possibility that the land may have been used for dumping first came to light last year.
Although the agencies have been aware of concerns about the site for some time, the Garda formally launched its own criminal investigation yesterday morning.
It involves gardaí from Navan and members of the National Bureau of Criminal Investigation.
The initial site sealed off by gardaí, and from which samples were taken yesterday to ascertain what is under the ground, measures 150m by 40m.
The site was identified in an EPA report published last year on the extent of "unauthorised waste activity".
The land was sold recently to a sport organisation, and it is accepted the group had no idea it may have been used for dumping.
A Garda source confirmed that one of the areas of concern is the proximity of the river Nanny.
A Meath County Council spokeswoman said the council was involved in a multi-agency operation "with a view to gaining a prosecution".
