On timely application in writing to the council, intervention shall be allowed to any person upon whom a statute confers a right to intervene and, in the discretion of the council, to any person having an interest in the subject matter and whose ability to protect such interest may be otherwise impaired or impeded. All petitions to intervene shall be verified under oath by the petitioner, shall adequately identify the petitioner, and shall establish with particularity an interest in the subject matter and that the ability to protect such interest may be otherwise impaired or impeded. In exercising discretion with regard to intervention, the council shall consider whether intervention by the petitioner would unduly delay the proceeding or prejudice the rights of the existing parties. The council may establish a date after which petitions to intervene will not be considered except for good cause shown. When such a date has been established, the council will assure that adequate public notice is given.