(a) Interveners. Responses to the petition must be filed at the time the motion to intervene is filed.

(b) Petitioner. The petitioner may respond to filings of another party within 15 days after service of such filings. Amended pleadings may be filed under Rule 215 (amendments) if the petitioner discovers facts unavailable at the time the initial petition was filed, or if such pleadings are requested or permitted by Staff under Rule 1107 (evaluations).