To the extent consistent with applicable provisions of the Federal Water Pollution Control Act, as now or hereafter amended, the Federal Safe Drinking Water Act (P.L. 93-523), as now or hereafter amended, the Clean Air Act as amended in 1977 (P.L. 95-95), and regulations pursuant thereto, and to the extent consistent with applicable provisions of the Federal Resource Conservation and Recovery Act of 1976 (P.L. 94-580), and regulations pursuant thereto:
     (a) The Board may grant individual variances beyond the limitations prescribed in this Act, whenever it is found, upon presentation of adequate proof, that compliance with any rule or regulation, requirement or order of the Board would impose an arbitrary or unreasonable hardship. However, the Board is not required to find that an arbitrary or unreasonable hardship exists exclusively because the regulatory standard is under review and the costs of compliance are substantial and certain. In granting or denying a variance the Board shall file and publish a written opinion stating the facts and reasons leading to its decision.
     (b) The Agency shall grant provisional variances whenever it is found, upon presentation of adequate proof, that compliance on a short term basis with any rule or regulation, requirement or order of the Board, or with any permit requirement, would impose an arbitrary or unreasonable hardship.