a) The degree of emission limitation required for control of any regulated NSR pollutant under this Part shall not be affected in any manner by:

1) So much portion of the stack height of any source that exceeds good engineering practice, or

2) Any other dispersion technique.

b) Except as provided in subsection (c), subsection (a) shall not apply with respect to stack heights in existence before December 31, 1970, or to dispersion techniques implemented before then.

c) Notwithstanding subsection (b), subsection (a) shall apply where regulated NSR pollutants are being emitted from such stacks or using such dispersion techniques by sources, as defined in section 111(a)(3) of the CAA (42 U.S.C. 7411(a)(3)), which were constructed, or reconstructed, or for which major modifications were carried out after December 31, 1970.

d) Subsection (a) shall not apply with respect to coal-fired steam electric generating units subject to the provisions of section 118 of the CAA (42 U.S.C. 7418), which commenced operation before July 1, 1957, and whose stacks were constructed under a construction contract awarded before February 8, 1974.

(Source: Added at 49 Ill. Reg. 6237, effective April 23, 2025)