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Federal Register / Vol. 86, No. 114 / Wednesday, June 16, 2021 / Rules and Regulations
ADEQs rationale.44 For example, the submittal explains that, in the ADEQs experience, most permitted sources include one or more pieces of equipment subject to an NSPS, such as boilers, stationary engines, or fuel storage tanks. The ADEQ clarified that a stationary source subject to such a standard could not make use of the agricultural equipment exemption.
The ADEQs submittal further explains that under section 111 of the Clean Air Act, EPA is required to maintain a list of, and adopt NSPS for, all categories of sources that cause or significantly contribute to air pollution which may reasonably be anticipated to endanger public health or welfare. The ADEQ notes that, consistent with the breadth of this charge, the EPA has adopted standards for dozens of common sources of criteria pollutants, criteria pollutant precursors, greenhouse gases, and other pollutants. The ADEQ
reasons that it is therefore likely that if equipment used in normal farm operations were collocated with equipment with stack emissions exceeding the permitting exemption thresholds, at least some of that equipment would be subject to an NSPS, and the exemption would not apply.45
We believe the ADEQs explanation to be sufficiently supported based on the ADEQs knowledge and experience with the pollutant-generating activities it oversees.46
Finally, the commenters challenge the ADEQs statement that in the few, if any, cases where equipment used in normal farm operations is located at a non-title V source that has stack emissions above the permitting exemption thresholds but does not include NSPS or NESHAP equipment, ADEQ retains the authority to require a 44 2020

Minor NSR submittal at 1213.
4.2.5 of the 2020 Minor NSR submittal at 12; see also the detailed discussion in section 4.2.5 of the 2020 Minor NSR submittal at 1213.
46 On the issue of the NSPS standards not applying during periods of startup, shutdown, or malfunction we disagree with this broad categorization, while the NAAQS do, we believe the commenters misunderstand how the ADEQs permitting program works and how the normal farm operations exemption would apply to a source that includes equipment subject to an NSPS. The ADEQ
does not allow stationary sources to use the agricultural equipment exemption to avoid NSR
review if the stationary source is also subject to a standard under 40 CFR parts 60, 61, or 63. This means that the entire stationary source becomes subject to the ADEQs permitting program, including potential NAAQS reviews for new or modified sources, if even a single piece of equipment is subject to an NSPS. The way the various NSPS apply in general during periods of startup, shutdown, or malfunction is not germane to the scope of the normal farm operations exemption.

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permit to the extent necessary to assure protection of the NAAQS and the control strategy. 47 The commenters express concern because they are unclear on how the ADEQ would know that a permit is needed or that there is a potential NAAQS issue if sources arent required to submit applications for review. We understand the commenters concern on this issue, because the NSR program is intended to require review of sources prior to construction or modification to ensure that sources and modifications are constructed in a manner that will not cause or contribute to a NAAQS
violation. However, our approval of the ADEQs agricultural equipment exemption under 40 CFR 51.160e is based on the totality of the information presented by the ADEQ in the 2020
Minor NSR submittal. The ADEQ has demonstrated that the exemption creates a narrow category of sources that may be exempt from minor NSR review, as compared to the program we have already approved. However, in the potential instances where a stationary source is otherwise not required to obtain a permit in advance, the ADEQ
has clarified that it has the authority to later require a permit and limit operations to protect the NAAQS. That is, minor sources defined as agricultural equipment used in normal farm operations cannot operate in a manner that would interfere with attainment and maintenance of the NAAQS by relying on the permitting exemption in State law.
In sum, the ADEQ has provided a detailed and well-supported rationale for its exemption of agricultural equipment used in normal farm operations from its minor NSR
program, and demonstrated that any potentially exempted sources are inconsequential to attainment and maintenance of the NAAQS. Further, because the exemption will not interfere with the NAAQS, it is consistent with CAA section 110l and section 2.2d of Appendix V to 40 CFR part 51.
Comment: The commenters state that the ADEQ failed to justify the exemption for certain small stationary fuel burning equipment rated at less than one million British thermal units per hour MMBtu/hr found in Arizona state law. The commenters are concerned that the ADEQs rationale does not justify the exemption or ensure protection of the NAAQS, as the ADEQ
did not present modeling or other evidence in support of the exemption or to support that this equipment would not otherwise require a permit.
47 2020

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Minor NSR submittal at 9.

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Response: We disagree with the commenters that the ADEQ has not adequately justified the Arizona state law exemption for small fuel burning equipment those rated at less than 1
MMBtu/hr in ARS section 49426B
within the context of its NSR program.
The ADEQs 2020 Minor NSR submittal provides an analysis of the state law exemption because the EPA identified it as a limited disapproval issue in our 2015 NSR action. In our 2015 NSR
action, we found that the ADEQs 2012
NSR submittal did not describe how the state law exemption for small fuel burning equipment applied in the context of its NSR program. Further, to the extent the ADEQs NSR program exempts some sources from minor NSR
review under the state law exemption, we found that the ADEQ needed to provide an adequate justification under 40 CFR 51.160e.48
In the 2020 Minor NSR submittal, the ADEQ confirmed that it interprets the exemption as 1 being available only to those stationary sources that consists solely of equipment with a cumulative heat input rate of less than 1 MMBtu/
hr, and 2 having already been effectively SIP-approved by the EPA
because all such equipment falls under the ADEQs existing SIP-approved exemption for categorically exempt activities at R182302C1 and R18
210123.49
As explained by the ADEQ in the 2020 Minor NSR submittal, the EPA
reviewed the ADEQs permitting and registration exemption for categorically exempt activities in our 2015 NSR
action. R182302C provides that a stationary source that consists solely of a single categorically exempt activity plus any combination of trivial activities 50 does not require a permit or registration, unless the source is a major source or operation without a permit would result in a violation of the Act.
The ADEQ defines a categorially exempt activity at R18210124 and it includes various categories of smaller fuel-burning equipment. For example, one category is any combination of diesel-, natural gasor gasoline-fired engines with cumulative power equal to or less than 145 horsepower and another is any combination of boilers with a cumulative maximum design heat input capacity of less than 10
million Btu/hr. The ADEQ explained in its 2012 NSR SIP submittal how the cumulative heat input or power rating 48 See section 5.2.2.3 of the EPAs 2015 TSD at 2627; 80 FR 67319, 67323.
49 See section 4.3 of the 2020 Minor NSR
submittal at 1314.
50 Trivial activities under the ADEQs permitting program are defined R182101146.

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