(1) A Montana air quality permit is not required under ARM 17.8.743 for de minimis changes as specified below:

(a) Construction or changed conditions of operation at a facility for which a Montana air quality permit has been issued that do not increase the facility's potential to emit by more than five tons per year of any pollutant except:

(i) any construction or changed conditions of operation at a facility that would violate any condition in the facility's existing Montana air quality permit or any applicable rule contained in this chapter is prohibited, except as allowed in (2);

(ii) any construction or changed conditions of operation at a facility that would qualify as a major modification of a major stationary source under subchapters 8, 9, or 10 of this chapter;

(iii) any construction or changed conditions of operation at a facility that would affect the plume rise or dispersion characteristics of the emissions in a manner that would cause or contribute to a violation of an ambient air quality standard or an ambient air increment, as defined in ARM 17.8.804;

(iv) any construction or improvement project with a potential to emit more than five tons per year may not be artificially split into smaller projects to avoid permitting under this subchapter; and

(v) emission reductions obtained through offsetting within a facility are not included when determining the potential emission increase from construction or changed conditions of operation, unless such reductions are made federally enforceable.

(b) The owner or operator of any facility making a de minimis change pursuant to (1)(a) shall notify the department if the change would include addition of a new emissions unit, a change in control equipment, stack height, stack diameter, stack flow, stack gas temperature, source location, or fuel specifications, or would result in an increase in source capacity above its permitted operation.

(c) The following are excluded from the notice requirements of (1)(b):

(i) day-to-day fluctuations of the parameters described in (1)(b), occurring as a result of the design or permitted operations of the facility, including startup and shutdown of emission sources at the facility; and

(ii) addition, modification, or replacement of pumps, valves, flanges, and similar emission sources. The department shall develop, maintain, and update a list of emission sources it believes qualify for exclusion from the notice requirements. Upon request, the department shall provide a copy of the list to interested persons.

(d) If notice is required under (1)(b), the owner or operator shall submit the following information to the department in writing at least ten days prior to startup or use of the proposed de minimis change or as soon as reasonably practicable in the event of an unanticipated circumstance causing the de minimis change:

(i) a description of the proposed de minimis change requiring notice, including the anticipated date of the change;

(ii) sufficient information to calculate the potential emissions resulting from the proposed de minimis change; and

(iii) if applicable, an explanation of the unanticipated circumstance causing the change.

(e) The notice requirements under (1)(d) do not supersede, or otherwise change, any requirements in 40 CFR Parts 60, 61, or 63.

(2) A Montana air quality permit may be amended pursuant to ARM 17.8.764, for changes made under (1)(a)(i) that would otherwise violate an existing condition in the permit. Conditions in the permit concerning control equipment specifications, operational procedures, or testing, monitoring, record keeping, or reporting requirements may be modified if the modification does not violate any statute, rule, or the state implementation plan. Conditions in the permit establishing emission limits, or production limits in lieu of emission limits, may be changed or added under (1)(a), if the owner or operator agrees to such changes or additions.