The Director General of the Environmental Protection Agency has said there is evidence that an illegal dump on land owned by Cement Roadstone in Blessington, Co Wicklow, is beginning to contaminate ground water at the site.
Mary Kelly was addressing the Joint Oireachtas Committee on the Environment and Local Government.
Ms Kelly said that it was the EPA's view that the problem of illegal dumping was worst in Wicklow and Kildare.
In Wicklow in particular, more than 100 sites of organised illegal dumping have now been identified.
But she said it would be 100 years before the Blessington contamination posed a threat.
Independent Senator Shane Ross congratulated the EPA for refusing to grant CRH a licence to put the contents of that illegal dump into a legal landfill on the site.
Labour's Liz McManus questioned why action against illegal dumping in Co Wicklow had been so slow to come before the courts.
She also questioned whether allowing people who had illegal dumps on their land to turn them into legal landfills was bad practice.
