(b) The Department may, after notice and opportunity for a public hearing, revise or modify a final compliance date for any stationary source or class or sources of air pollution whether contained in regulations or a compliance order, if the Department determines that

1. (1) good faith efforts have been made to comply with such requirement before such date;
2. (2) such source (or class) is unable to comply with such requirement because the necessary technology or other alternative methods of control are not reasonably available or have not been available for a sufficient period of time;
3. (3) any available alternative operating procedures and interim control measures have reduced or will reduce the impact of such source on public health;

4. (4) the continued operation of such source is essential to national security or to the public health or welfare.

   Provided, however, that where the compliance date is one prescribed in the State Implementation Plan, the findings and recommendations of the Department shall be submitted to the Governor for transmittal to the Administrator of the Federal Environmental Protection Agency or his designated representative for his concurrence or rejection. Rejection by the administrator may constitute grounds for rejection of a request for modification or revisions of such compliance requirement.