The applicant or permittee shall be made a party to any adjudicatory hearing involving a permit application or permit under the Regulatory Program. The Bureau shall in all cases be made a party to any adjudicatory hearing under the Regulatory Program. Any person may be granted intervention as a party upon a showing, before the beginning of the hearing, that they would have been entitled to request a hearing in their own right, and that existing parties cannot be expected to adequately represent their interests.