The Indiana Supreme Court has recently decided what this means in Huffman v. Indiana Office of Enviromental Adjudications, et al.  811 N.E.2d 806 (Ind. 2004). You must state in your Petition for Review that you have suffered or are "likely to suffer in the immediate future, harm to a legal interest, whether it pecuniary, property or personal interest." This means that you have to state how you personally have been injured by the IDEM action. This cannot be an injury suffered by a neighbor or to the general public.