Any person, including the Secretary of the United States Department of Interior, may petition for leave to intervene at any stage of an administrative proceeding under this subtitle. A petitioner for leave to intervene shall incorporate in the petition a statement setting forth the interest of the petitioner and a showing of why the petitioner's interest is or may be adversely affected. Intervention shall be granted if the petitioner: Had a statutory right to initiate the proceeding in which the petitioner wishes to intervene; or Has an interest which is or may be adversely affected by the outcome of the proceeding. If neither §C(1) nor (2) of this regulation applies, the following shall be considered in determining whether intervention is appropriate: The nature of the issues; The adequacy of representation of petitioner's interest which is provided by the existing parties to the proceeding; The ability of the petitioner to present relevant evidence and argument; and The effect of intervention on the Department's implementation of its statutory mandate. Any person granted leave to intervene in a proceeding may participate in this proceeding as a full party or, if desired, in a capacity less than that of a full party. If the intervenor wishes to participate in a limited capacity, the extent and terms of the participation shall be in the discretion of the Department.