a) Except as provided in subsections (d) through (f) below, "major modification" means any physical change or change in the method of operation of a major stationary source that would result in: a significant emissions increase (as defined in Section 203.1380) of a regulated NSR pollutant (as defined in Section 203.1340); and a significant net emissions increase of that regulated NSR pollutant for which the source is a major stationary source.

b) Any significant emissions increase (as defined in Section 203.1380) from any emissions units or net emissions increase (as defined in Section 203.1260) at a major stationary source that is significant for VOM or NO_X shall be considered significant for ozone.

c) A physical change or change in the method of operation shall not include:

1) Routine maintenance, repair and replacement;

2) Use of an alternative fuel or raw material by reason of:

A) An order under Section 2(a) and (b) of the Energy Supply and Environmental Coordination Act of 1974 (15 U.S.C. 791) (or any superseding legislation); or

B) A natural gas curtailment plan under the Federal Power Act (16 U.S.C. 791);

3) Use of an alternative fuel by reason of an order or rule under section 125 of the CAA (42 U.S.C. 7425);

4) Use of an alternative fuel at a steam generating unit to the extent that the fuel is generated from municipal solid waste;

5) Use of an alternative fuel or raw material by a stationary source which:

A) The source was capable of accommodating before December 21, 1976, unless such change would be prohibited under any federally enforceable permit condition which was established after December 21, 1976, pursuant to 40 CFR 52.21, 35 Ill. Adm. Code 204, this Part, or 35 Ill. Adm. Code 201.142 or 201.143; or

B) The source is approved to use under any permit issued under 40 CFR 52.21, this Part, 35 Ill. Adm. Code 204, or 35 Ill. Adm. Code 201.142 or 201.143;

6) An increase in the hours of operation or in the production rate, unless such change is prohibited under any enforceable permit condition which was established after December 21, 1976 pursuant to 40 CFR 52.21, 35 Ill. Adm. Code 204, this Part, or 35 Ill. Adm. Code 201.142 or 201.143; or

7) Any change in ownership at a stationary source.

d) In the case of any major stationary source of VOM or NO_X located in an area classified as serious or severe nonattainment for ozone (other than a source which emits or has the potential to emit 100 tons or more of VOM or NO_X per year), whenever any change at that source results in a significant increase in emissions of VOM or NO_X, respectively, from any discrete operation, unit, or other pollutant emitting activity at the source, such increase shall be considered a major modification for purposes of this Part, except such increase shall not be considered a major modification for such purposes if the owner or operator of the source elects to offset the increase by a greater reduction in emissions of VOM or NO_X, respectively, from other operations, units, or activities within the source at an internal offset ratio of at least 1.3 to 1.

e) In areas classified as extreme nonattainment for ozone, beginning on the date that an area is classified by the USEPA as an extreme nonattainment area for ozone, any physical change in or change in the method of operation of a major stationary source which results in any increase in emissions of VOM or NO_X from a discrete operation, unit, or other pollutant emitting activity shall be considered a major modification.

f) This definition shall not apply with respect to a particular regulated NSR pollutant when the major stationary source is complying with the requirements under Subpart Q for a PAL for that pollutant. Instead, the definition at Section 203.2230 will apply.

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