Dear Ms. Thompson,

            On November 3, 2025, the Virginia Department of Environmental Quality (DEQ) opened a public comment period on proposed Guidance Memo APG-578, which interprets the term “emergency” in the Virginia Air Pollution Control regulations to include “planned outages.”[1] This guidance would allow a permitted source to run diesel-fired, portable “Tier 2” emergency generators when an electricity service provider has given notice 14 days or less in advance of a planned electrical outage.[2] This marks a change from DEQ’s previous position that a planned electrical outage was not an “emergency” under the regulations.[3] As explained below, DEQ’s new interpretation conflicts with the plain language of the regulations. In other words, the proposed guidance is not guidance at all, but rather amounts to amending a regulation without adhering to the rulemaking procedures required under the Virginia Administrative Process Act (“VAPA”).[4] DEQ should therefore withdraw Guidance Memo APG-578 or, if it wishes to continue with this action, follow the proper rulemaking procedures. At a minimum, given the legal flaws, DEQ must delay the memo’s effective date by 30 days.[5]

            Federal and state regulations limit the use of Tier 2 diesel-fired generators to emergencies[6] for good reason: Tier 2 generators cause severe air pollution. These generators emit substantial quantities of nitrous oxides, which contribute to ground-level ozone pollution and acid rain.[7] They also emit more carbon monoxide, particulate matter, and other pollutants than newer Tier 4 generators and other cleaner technologies.[8] Exposure to these pollutants can damage humans’ cardiovascular, respiratory, and central nervous systems.[9] Although data centers’ diesel generators currently make up a relatively small percentage of regional emissions of these pollutants, local effects may be substantial because data centers (and their generators) are highly concentrated in certain localities.[10] In a community like eastern Loudoun County, where 4,700 diesel generators are permitted, an emergency outage in which thousands of Tier 2 generators run at the same time could pose a dire threat to public health.[11]

All of these harms will be exacerbated by Guidance Memo APG-578, which will allow Tier 2 generators to run more often by extending the definition of an “emergency” to include planned outages. And, as DEQ acknowledges, allowing Tier 2 generators to run during planned outages will lessen the incentive for laggards to transition to Tier 4 generators or even cleaner technologies such as batteries.[12] The guidance will thus undermine DEQ’s own policy that “strongly encourages” sources to use Tier 4 generators or cleaner technologies.[13]  

But even setting aside the adverse effects on human health and air quality that will result from Guidance Memo APG-578, the memo is unlawful because it conflicts with the plain text and context of the regulation it interprets. An agency must interpret unambiguous provisions of a regulation consistent with their plain language.[14] Under the State Air Pollution Control Board  (“Air Board”) regulations governing emergency generators, an “emergency” is “a condition that arises from sudden and reasonably unforeseeable events where the primary energy or power source is disrupted or disconnected due to conditions beyond the control of an owner” of a facility.[15] Although “sudden” and “unforeseeable” are not defined in the regulations, each word’s ordinary meaning implies an unexpected event—a lack of notice.[16] When an owner of a source receives notice of a planned outage, that outage can, by definition, be foreseen by the owner. It thus cannot be an “emergency” under the regulation’s plain language. Indeed, DEQ relied on this exact rationale in its previous policy (up until this guidance document) of interpreting the definition of an “emergency” to exclude planned outage events.[17]

In adopting its new position, DEQ skirts this obvious conclusion by suggesting that the terms “‘sudden’ and ‘reasonably unforeseeable’ must be understood in context,”[18] yet the broader context of the regulation actually cuts against its interpretation. When a statute or regulation uses a general term followed by a list of specific examples, the examples are typically understood to limit the general term’s scope.[19] Here, the regulations list several examples of a “sudden and reasonably unforeseeable event”: (1) a “failure of the electrical grid”; (2) an “[o]n-site disaster or equipment failure”; (3) “[p]ublic service emergencies such as flood, fire, natural disaster, or severe weather conditions”; and (4) an “ISO-declared emergency,” such as an “abnormal system condition requiring . . . action to maintain system frequency, to prevent loss of firm load, equipment damage, or tripping of system elements,” a capacity deficiency or excess, or a fuel shortage.[20] Although this enumerated list is not exhaustive, the examples provided—fires, floods, disasters, grid failures—are circumstances that any layperson would describe as an “emergency.”[21] That strongly suggests that when the Air Board limited the definition of an “emergency” to a “sudden and reasonably unforeseeable event,” it was thinking about severe and extreme circumstances—in other words, true emergencies. Planned outages with up to two weeks’ notice do not fit in that category.

When a comment filed during a public comment period asserts that a guidance document is “contrary to state law or regulation” or “should not be exempted from the provisions of [the VAPA],” the agency must delay the effective date of the guidance document for an additional 30 days and respond to the comment in writing.[22] Both rationales for a 30-day delay apply here. As explained above, Guidance Memo APG-578 is contrary to law because planned outages are not “emergencies” within the meaning of 9VAC5-540-20 and 9VAC5-80-1110. And because the memo amounts to DEQ impermissibly amending the regulatory definition of an “emergency,” it should not be exempt from the VAPA.[23] DEQ cannot alter the plain meaning of regulations through guidance memos.[24] The only way that a planned outage can be classified as an emergency is if the Air Board amends the definitions of “emergency” in 9VAC5-540-20 and 9VAC5-80-1110 through the VAPA’s full notice and comment process for regulations.[25]

For the reasons above, DEQ should withdraw Guidance Memo APG-578 and must, at minimum, delay its effective date by 30 days.

Respectfully submitted,