For the purposes of this subchapter:
(1) "Alternative mercury emission limit" means a mercury emission limit for a mercury-emitting generating unit, established by the department in a permit issued or modified pursuant to 75-2-211, MCA, in lieu of compliance with ARM 17.8.771(1)(a).
(2) "Best available control technology (BACT)" means an emission limitation (including a visible emission standard), based on the maximum degree of reduction for each pollutant subject to regulation under 42 U.S.C. 7410, et seq. or 75-2-101, et seq., MCA, that would be emitted from any proposed emitting unit or modification which the department, on a case-by-case basis, taking into account energy, environmental, and economic impacts and other costs, determines is achievable for such emitting unit or modification through application of production processes or available methods, systems, and techniques, including fuel cleaning or treatment or innovative fuel combustion techniques for control of such contaminant. In no event may application of BACT result in emission of any regulated air pollutant that would exceed the emissions allowed by any applicable standard under ARM Title 17, chapter 8, subchapter 3, and this subchapter. If the department determines that technological or economic limitations on the application of measurement methodology to a particular class of emitting units would make the imposition of an emission standard infeasible, it may instead prescribe a design, equipment, work practice, or operational standard or combination thereof, to require the application of BACT. Such standard must, to the degree possible, set forth the emission reduction achievable by implementation of such design, equipment, work practice, or operation and must provide for compliance by means that achieve equivalent results.
(3) "Commercial operation" means the time when the owner or operator supplies electricity for sale.
(4) "Construct" or "construction" includes a reasonable period of time for startup and shakedown and means:
(a) initiation of on-site fabrication, erection, or installation of an emitting unit or control equipment including, but not limited to:
(i) installation of building supports or foundations;
(ii) laying of underground pipework; or
(iii) construction of storage structures; or
(b) the installation of any portable or temporary equipment or facilities.
(5) "Day" means calendar day unless otherwise stated.
(6) "Emitting unit" means:
(a) any equipment that emits or has the potential to emit any regulated air pollutant under the Clean Air Act of Montana through a stack(s) or vent(s); or
(b) any equipment from which emissions consist solely of fugitive emissions of a regulated air pollutant under the Clean Air Act of Montana.
(7) "Existing emitting unit" means an emitting unit that was in existence and operating or was capable of being operated on March 16, 1979, or for which the department had issued a permit by that date.
(8) "Facility" means any real or personal property that is either stationary or portable and is located on one or more contiguous or adjacent properties under the control of the same owner or operator and that emits or has the potential to emit any air pollutant subject to regulation under the Clean Air Act of Montana or the Federal Clean Air Act, including associated control equipment that affects or would affect the nature, character, composition, amount, or environmental impacts of air pollution and that has the same two-digit standard industrial classification code. A facility may consist of one or more emitting units.
(9) "Install" or "installation" means to set into position and connect or adjust for use.
(10) "Maximum design heat input" has the meaning as defined in 40 CFR 60.4102.
(11) "Mercury" means mercury or mercury compounds in either a gaseous or particulate form.
(12) "Mercury-emitting generating unit" means any emitting unit at a facility for which an air quality permit is required pursuant to 75-2-211 or 75-2-217, MCA, that generates electricity and combusts coal, coal refuse, or a synthetic gas derived from coal and that is defined as an electrical generating unit under 40 CFR 60.24.
(13) "Mercury-emitting generating unit that combusts lignite" means any mercury-emitting generating unit that combusts lignite in an amount equal to or greater than 75% of its total heat input, calculated for the prior calendar year on a calendar year basis.
(14) "Modify" does not include routine maintenance, repair, or replacement but means:
(a) construction or changes in operation at a facility or emitting unit for which the department has issued a Montana air quality permit under this chapter, except when a permit is not required under ARM 17.8.745;
(b) construction or changes in operation at a facility or emitting unit for which a Montana air quality permit has not been issued under this chapter but that subjects the facility or emitting unit to the requirements of ARM 17.8.743;
(c) construction or changes in operation at a facility or emitting unit that would violate any condition in the facility's Montana air quality permit, any board or court order, any control plan within the Montana state implementation plan, or any rule in this chapter, except as provided in ARM 17.8.745;
(d) construction or changes in operation at a facility or emitting unit that would qualify as a major modification of a major stationary source under subchapters 8, 9, or 10 of this chapter;
(e) construction or changes in operation at a facility or emitting unit that would affect the plume rise or dispersion characteristics of 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; or
(f) any change in operation that affects emissions and that was not previously permitted, except that a change in operation that does not result in an increase in emissions because of the change is not a modification.
(15) "Montana air quality permit" means a preconstruction permit issued under this subchapter that may include requirements for the construction and subsequent operation of an emitting unit(s) or facility.
(16) "Negligible risk to the public health, safety, and welfare and to the environment" means an increase in excess lifetime cancer risk of less than 1.0 x 10-6, for any individual pollutant, and 1.0 x 10-5, for the aggregate of all pollutants, and an increase in the sum of the noncancer hazard quotients for all pollutants with similar toxic effects of less than 1.0, as determined by a human health risk assessment conducted according to ARM 17.8.767. The department shall also consider environmental impacts identified in any environmental analysis conducted pursuant to the Montana Environmental Policy Act, Title 75, chapter 1, parts 1 through 3, MCA, in determining compliance with all applicable rules or other requirements requiring protection of public health, safety, and welfare and the environment.
(17) "New or modified emitting unit" means an emitting unit that was not constructed or upon which construction was not commenced prior to March 16, 1979.
(18) "Owner or operator" means the owner of a facility or other person designated by the owner as responsible for overall operation of the facility.
(19) "Potential to emit" means the maximum capacity of a facility or emitting unit, within physical and operational design, to emit a pollutant. Any physical or operational limitation on the capacity of the facility or emitting unit to emit a pollutant, including air pollution control equipment and restrictions on hours of operation or on the type or amount of material combusted, stored, or processed, is treated as part of its design only if the limitation or the effect it would have on emissions is federally enforceable. Secondary emissions are not considered in determining potential to emit.
(20) "Routine maintenance, repair, or replacement" means any action taken upon an emitting unit by the owner or operator that is necessary on a periodic basis to assure proper operation of the emitting unit. The term routine does not include activities that:
(a) have associated fixed capital costs in excess of 50% of the fixed capital cost necessary to construct a comparable, entirely new emitting unit;
(b) change the design of the emitting unit, including associated control equipment; or
(c) increase the potential to emit of the emitting unit.
(21) "Secondary emissions" means emissions that would occur as a result of the construction or operation of a facility or emitting unit, but do not come from the facility or emitting unit itself. Secondary emissions must be specific, well defined, quantifiable, and impact the same general area as the facility or emitting unit which causes the secondary emissions. Secondary emissions may include, but are not limited to:
(a) emissions from trains coming to or from the facility or emitting unit;
(b) emissions from any off-site support facility that otherwise would not be constructed or increase its emissions as a result of the construction or operation of the facility or emitting unit.