(a) The Administrator may, upon notice and opportunity for public hearing, exempt the owner or operator of any source from a penalty where he finds that a particular instance of noncompliance was de minimis in nature and duration.

(b) A petition for an exemption on the ground that the violation described in a notice of noncompliance was de minimis in nature and duration may only raise issues related to entitlement to an exemption and shall contain or be accompanied by supporting documentation. Issues relating to entitlement to a de minimis exemption not raised in the petition shall be deemed waived.

(c) In ruling upon such a petition, the Administrator shall consider:

(1) The magnitude of the excess emissions and whether the source's noncompliance is recurring or persistent;

(2) The steps the source owner or operator is taking to eliminate the cause of the excess emissions and to minimize such emissions;

(3) Whether any significant economic savings are likely to accrue to the owner or operator of the source as a result of the noncompliance;

(4) The character of the emissions, and their impact on ambient air quality; and

(5) The duration of the violation.

(d) A hearing on a petition for a de minimis exemption shall be informal. The hearing shall be scheduled upon notice to the public. Reasonable opportunity to testify and for submission of questions by the public to the petitioner shall be afforded. The decision of the hearing officer will be made in writing within a reasonable period of time after the close of the hearing.