Authority: IC 13-14-8; IC 13-17-3-4; IC 13-17-3-11

Affected: IC 13-17

Sec. 4. (a) For the purpose of establishing limits on the maximum stack height credit to be used in ambient air quality modeling and for calculating the air quality impact of a source, the stack height shall be the greater of:

1. (1) 65 meters;

2. (2) for stacks in existence on or before January 12, 1979, and for which the owner or operator had all applicable preconstruction permits or approvals as required by 326 IAC 2:

   1. Hg = 2.5H;

3. (3) for stacks in existence after January 12, 1979:

   1. Hg = H + 1.5L, where:

      1. Hg = GEP height, measured from the ground level elevation at the base of the stack.
      2. H = Height of nearby structure(s) measured from the ground elevation at the base of the stack.
      3. L = Lesser dimension (height or projected width) of nearby structures.

The commissioner shall require fluid modeling and field studies in cases where the commissioner believes the formulas may significantly overstate the appropriate stack height credit.

(b) Sources shall be modeled at the physical stack height. If the physical stack height exceeds GEP stack height, GEP stack height shall be used in modeling.

(c) The stack height demonstrated by a fluid model or field study, approved by the commissioner, shall ensure that emissions from a stack do not result in excessive concentrations of any pollutant as a result of atmospheric downwash, wakes, or eddy effects created by the source itself, structures, or terrain.

(d) Emission limitations required for any source shall not be affected by the stack height that exceeds GEP or by any other dispersion technique, except as provided below in subsections (e) and (f) of this section.

(e) Sources which merged stacks before July 8, 1985, can receive credit for such merging if it was done to install pollution control equipment or for other engineering or economic reasons and generally did not result in an emission increase at the source.

(f) Sources which merge stacks after July 8, 1985, will only be granted credit for merging where reductions in the allowable emission rate occurs.

(g) The commissioner shall notify the public of the availability of the stack height demonstration study required by this section, and shall provide the opportunity for a public hearing on said study.

(Air Pollution Control Division; 326 IAC 1-7-4; filed Mar 10, 1988, 1:20 pm: 11 IR 2383; readopted filed Jan 10, 2001, 3:20 p.m.: 24 IR 1477; readopted filed Oct 18, 2024, 2:09 p.m.: 20241113- IR-326230809RFA)