extend the period of a preliminary permit once for not more than 4 additional years beyond the 4 years permitted by subsection (a) if the Commission finds that the permittee has carried out activities under such permit in good faith and with reasonable diligence; and

after the end of an extension period granted under paragraph (1), issue an additional permit to the permittee if the Commission determines that there are extraordinary circumstances that warrant the issuance of the additional permit.