((a)) ** Temporary exemption due to lack of alternate fuel supply, site limitations, or environmental requirements** After consideration of a petition (and comments thereon) for an exemption from one or more of the prohibitions of part A for a powerplant, the Secretary shall, by order, grant such an exemption for the use of natural gas or petroleum, if he finds that the petitioner has demonstrated that for the period of the proposed exemption, despite diligent good faith efforts—

((1)) it is likely that an adequate and reliable supply of coal or other alternate fuel of the quality necessary to conform with design and operational requirements for use as a primary energy source, will not be available to such powerplant at a cost (taking into account associated facilities for the transportation and use of such fuel) which, based upon the best practicable estimates, does not substantially exceed the costs, as determined by rule by the Secretary, of using imported petroleum as a primary energy source;

((2)) one or more site limitations exist which would not permit the operation of such a powerplant using coal or any other alternate fuel as a primary energy source; or

((3)) the prohibitions of could not be satisfied without violating applicable environmental requirements.

((b)) ** Temporary exemption based upon future use of synthetic fuels** After consideration of a petition (and comments thereon) for an exemption from one or more of the prohibitions of part A for a powerplant, the Secretary, by order, shall grant an exemption under this subsection for the use of natural gas or petroleum, if he finds that the petitioner has demonstrated that—

((1)) the petitioner will comply with the prohibitions of part A by the end of the proposed exemption by the use of a synthetic fuel derived from coal or another alternate fuel; and

((2)) the petitioner is not able to comply with such prohibitions by the use of such synthetic fuel until the end of the proposed exemption.

((c)) ** Temporary exemption based upon use of innovative technologies** After consideration of a petition (and comments thereon) for an exemption from one or more of the prohibitions of part A for a powerplant, the Secretary, by order, shall grant an exemption under this subsection for the use of natural gas or petroleum, if he finds that the petitioner has demonstrated that such powerplant will comply with such prohibitions at the expiration of such exemption by the adoption of a technology for the use of coal or another alternate fuel which at the time of the granting of the exemption is determined by the Secretary to be an innovative technology. The effectiveness of an exemption under this subsection is conditioned on the petitioner filing and maintaining a compliance plan meeting the requirements of .section 8354(b) of this title

((d)) ** Temporary exemption for units to be retired**

((1)) After consideration of a petition (and comments thereon) for an exemption from one or more of the prohibitions of part A for a powerplant, the Secretary shall, by order, grant an exemption under this subsection for the use of natural gas or petroleum, if he finds that the petitioner has demonstrated that such powerplant is to permanently cease operation at or before the expiration of the exemption period. An exemption under this subsection is conditioned on the petitioner filing and maintaining a compliance plan meeting the requirements of section 8354(b) (other than paragraph (1)(B)) of this title.

((2)) Notwithstanding any other provision of this chapter, an exemption under this part may not be granted for any powerplant once an exemption under this subsection has been granted for such powerplant.

((e)) ** Temporary public interest exemption** After consideration of a petition (and comments thereon) for an exemption for a powerplant from one or more of the prohibitions of part A for a powerplant, the Secretary may, by order, grant an exemption under this subsection for the use of natural gas or petroleum, if he finds that the petitioner has demonstrated that for the period of the proposed exemption the issuance of such exemption is in the public interest and is consistent with the purposes of this chapter.

((f)) ** Temporary exemption for peakload powerplants** After consideration of a petition (and comments thereon) for an exemption from one or more of the prohibitions of part A for a powerplant, the Secretary shall, by order, grant an exemption under this subsection for the use of natural gas or petroleum, if the petitioner certifies that such powerplant is to be operated solely as a peakload powerplant.

((g)) ** Temporary exemption for powerplants where necessary to maintain reliability of service**

((1)) After consideration of a petition (and comments thereon) for an exemption from one or more of the prohibitions of part A for a powerplant, the Secretary shall, by order, grant an exemption under this subsection for the use of natural gas or petroleum, if he finds that the petitioner has demonstrated that such exemption is necessary to prevent impairment of reliability of service.

((2)) Notwithstanding any other provision of this chapter, an exemption under this part (other than a permanent exemption under for the use of petroleum) may not be granted for any powerplant for which an exemption under this subsection has been granted.

((h)) ** Duration of temporary exemptions**

((1)) Except as provided in paragraphs (2) and (3), exemptions under this section for any powerplant may not exceed, taking into account any extension or renewal, 5 years.

((2))

((A)) An exemption under subsection (a)(1) may be granted for a period of more than 5 years, but may not exceed, taking into account any extension or renewal, 10 years.

((B)) Subject to paragraph (3), an exemption under subsections (b), (c), and (g) may be extended beyond the 5-year limit under paragraph (1), but such exemption, so extended, may not exceed 10 years.

((3)) An exemption under subsections (d), (f), and (g) for the use of natural gas by a powerplant may not extend beyond .

((4)) In computing the 5-year and 10-year limitations of paragraphs (1) and (2) in the case of any exemption under this section, the period before the prohibition on the use of natural gas and petroleum would first apply (if the exemption had not been granted) shall be disregarded.