On behalf of its more than 15,000 Virginia members, the Sierra Club submits these comments opposing Virginia Department of Environmental Quality’s (DEQ) proposed changes to Guidance Document APG-578 “Sudden and Reasonably Unforeseeable Events in the Context of Planned Electric Outages.” The proposed changes would be contrary to the plain language of 9VAC5-540-20 and 9VAC5-80-1110 (definition of “emergency”) and a violation of the Administrative Procedures Act’s requirement to undertake rulemaking to substantively change a regulation. By expanding the definition of “emergency” to include planned outages, DEQ is violating its statutory directive to maintain and improve air quality by allowing dirty, Tier 2 diesel generators to operate more frequently, when there are other, cleaner, alternatives.
Comment No. 1 A planned outage is not an “emergency.”
DEQ seeks to change its interpretation of “sudden and reasonably unforeseeable events” as that term is used in defining an “emergency” for purposes of when emergency generators can be used and still be subject to less stringent requirements. Currently, DEQ interprets “sudden and reasonably unforeseeable events” as not including scheduled or planned power outages associated with electricity service provider activities. Now, however, DEQ seeks to expand the definition of “emergency” to include scheduled and planned outages simply because a permittee has a limited number of alternative power supplies, namely portable generators or Tier 4 controlled generators. This “new” interpretation directly conflicts with the plain language of 9VAC5-540-20 and 9VAC5-80-1110 and is an affront to DEQs responsibility to maintain and improve air quality. Expanding when a dirty diesel generator can be operated will do the exact opposite - it will worsen air quality.
“The primary objective in statutory construction is to determine and give effect to the intent of the legislature as expressed in the language of the statute.” Appalachian Power Co. v. State Corp. Comm'n, 284 Va. 695, 706 (2012). When a statute is unambiguous, we must apply the plain meaning of that language. Id. “Rules of statutory construction prohibit adding language to or deleting language from a statute.” BBF, Inc. v. Alstom Power, Inc., 274 Va. 326, 331, 645 S.E.2d 467, 469 (2007).
That being said, Virginia law clearly defines “emergency" as “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 source.” 9VAC5-540-20 and 9VAC5-80-1110 (emphasis added). In addition, “sudden” is commonly defined as “happening or coming unexpectedly” while “unforeseeable” is commonly defined as “not able to be reasonably anticipated or expected.” See https://www.merriam-webster.com/dictionary. Both of these dictionary definitions are consistent with the the four events that Virginia law has identified as “emergencies:” (1) failure of the electrical grid; (2) [o]n-site disaster or equipment failure; (3) [p]ublic service emergencies; and (4) ISO-declared emergenc[ies]. 9VAC5-540-20 and 9VAC5-80-1110. All of these events happen unexpectedly and are not reasonably anticipated.
Conveniently, DEQ does not define a planned outage in APG-578, however, according to Dominion Energy, “[a] planned outage is when we temporarily turn off power for scheduled work like maintenance or upgrades, and you're notified ahead of time.” In contrast, “an unplanned outage happens unexpectedly due to events like storms or accidents, with no warning.” See https://www.dominionenergy.com/virginia/report-outage-or-emergency/planned-outages. (emphasis added). Therefore, planned outages, by definition, are not emergencies; they are expected, reasonably anticipated and are in fact scheduled so customers can prepare in advance for an upcoming outage.
Not only are planned outages expected, they also happen regularly. Dominion Energy and other electric service providers have been planning and scheduling power outages for as long as they have been operating the electrical grid and are tracked in a service provider's SAIFI score (System Average Interruption Frequency Index - measures the frequency of interruptions in number of occurrences). Planned outages are used when a provider needs to conduct tree trimming, preventative maintenance, equipment upgrades, placing lines underground, or even to exchange service meters. Planned outages are not new and customers with backup diesel generators are accustomed to making the necessary arrangements whenever they are notified of a planned outage, whether that is bringing in mobile units, Tier 4 generators, or operating their home or business without power. For context, Dominion Energy customers experienced 1.6 interruptions/yr with a duration of 150 minutes/yr while Appalachian Power customers experienced 1.2 interruptions/yr with a duration of 350 minutes/yr in 2024 (excluding major storms). See Annual Report on Grid Modernization at 6-7 (December 1, 2025), available at https://rga.lis.virginia.gov/Published/2025/RD916/PDF. These non-major outages (or planned outages) do not meet the definition of an “emergency” as currently defined in 9VAC5-540-20 and 9VAC5-80-1110, or as described by electric service providers like Dominion Energy. As discussed below, if DEQ wants to expand the definition of “emergency” then it must go through the rulemaking process.
Comment No.2 DEQ cannot change the definition of “emergency” through guidance.
DEQ claims it is simply changing its interpretation of “sudden and reasonably unforeseeable events” to include scheduled and planned outages, even when the electric service provider gives advanced notice. However, this change in “interpretation” cannot be done through guidance, since it is substantively expanding the definition of an emergency under 9VAC5-540-20 and 9VAC5-80-1110, it must be done through rulemaking.
A “guidance document is any “document developed by a state agency or staff that provides information or guidance of general applicability to the staff or public to interpret or implement statutes or the agency's rules or regulations, excluding agency minutes or documents that pertain only to the internal management of agencies.” Va. Code. 2.2-4002.1. On the other hand, a “rule” or “regulation” is “any statement of general applicability, having the force of law, affecting the rights of conduct of any person, adopted by an agency in accordance with the authority conferred on it by applicable basic laws.” Id. Therefore, under the Virginia APA, the key distinction is whether the statement has the "force of law.” If it does, then it is a rule. See Dep't of Taxation v. 1887 Holdings, Inc., 77 Va. App. 653, 665, 887 S.E.2d 176 (2023).
As stated in Comment No.1, DEQs new interpretation expands the definition of an emergency to specifically include anticipated, foreseeable and “planned” events, thereby taking it out of the four categories of “emergency” identified in 9VAC5-540-20 and 9VAC5-80-1110. By doing so, DEQ is substantively changing the scope of what qualifies as an emergency. Through this interpretation, DEQ is authorizing permittees to operate their Tier 2 emergency diesel generators in scenarios unforeseen by the current statutory framework. Without this “new” interpretation, permittees would be violating the terms of their air permits (and subject to penalties) if they operated their emergency Tier 2 diesel generators in “non-emergency” situations such as planned outages, thereby giving this new “interpretation” the full force of law. If DEQ wants to expand the definition of “emergency” then it must go through the rulemaking process and change the definitions found in 9VAC5-540-20 and 9VAC5-80-1110.
Comment No. 3: Batteries are a better, cleaner alternative that should be required during scheduled or planned outages.
Battery backups combined with renewable energy is a better, cleaner alternative to operating Tier 2 diesel generators while protecting the community’s air quality. Renewable energy and battery storage is an investment, but it will pay for itself over time. Battery prices have reached record lows in recent years. See https://about.bnef.com/blog/lithium-ion-battery-pack-prices-see-largest-drop-since-2017-falling-to-115-per-kilowatt-hour-bloombergnef/. The payback period could also be shortened considerably when the alternative is considered: running diesel generators that have costly and often volatile fuel prices. Battery storage would provide the same dispatchable firm capacity value as a diesel generator, and batteries are readily available and cost-competitive. As an example, Google is using battery-based systems to replace their back-up diesel generators. See GOOGLE, 24/7 Carbon-Free Energy: Powering up new clean energy projects across the globe (Apr. 21, 2022), available at https://bit.ly/407WUwW. If DEQ is concerned that permittees cannot comply with the terms of their permit and continue to operate during scheduled and planned outages, then instead of expanding the definition of an emergency, which will lead to an increase in harmful air emissions, DEQ should instead require or encourage permittees to use battery storage during these planned events. As stated previously, the permittees are given advance notice by the electric service provider of an upcoming outage, and could easily switch to their backup batteries during these short events (Dominion reported 1.6 interruptions/yr with a duration of 150 minutes/yr for non-storm outages).
Comment No. 4. DEQ should require permittees to implement load flexibility measures to shift load during planned outages.
Load flexibility has become an increasing area of focus across the Commonwealth, including the State Corporation Commission (SCC). In Docket PUR-2025-00144 the SCC is hosting a technical conference on December 12, 2025 to solicit information on the ability to shift or reduce electricity consumption in response to grid conditions, such as during peak demand hours. But load shifting (or interruptibility) could also include planned or scheduled outages. Load flexibility can be divided generally into static and dynamic flexible connections. Static flexible connections allow customers to modify their load profile to avoid system constraints using technologies such as energy management systems, behind-the-meter generation, or on-site storage. Dynamic flexible connections include actively managed connections as well as day-ahead scheduling (e.g., dynamic operating envelopes) by the electric service provider. Emerald AI, funded in part by The Electric Power Research Institute’s DCFlex data center flexibility initiative, recently released data from a demonstration of new active management capabilities. See Electric Power Research Institute, DCFlex Initiative, http://dcflex.epri.com Emerald AI demonstrated the capability to reduce processing power consumption by 25% over a three-hour period, while maintaining performance above 90% of full-load capability. See Marc Spieler, How AI Factories Can Help Relieve Grid Stress, NVDIA (July 1, 2025), available at http://bit.ly/466u2ee
The active management of the load can also allow customers to integrate behind-the-meter resources to fill in periods when the system is stressed or when there is a planned outage. These tools are already being piloted by Google. As an example, a grid operator notifies Google about a forecasted supply constraining event (like extreme weather), and the relevant data centers receive instructions to limit non-urgent tasks for a specific window of time. “Google’s algorithms then generate an enhanced capacity curve that creates hour-by-hour use instructions, which can include pausing flexible workloads like YouTube video processing or rerouting certain tasks to data centers on a different power grid.” See https://www.latitudemedia.com/news/google-datacenters-demand-response/.
Instead of allowing permittees to use their dirty, polluting Tier 2 diesel generators during planned outages, DEQ should require or encourage them to install technology that would allow them to shift their load when they are given notice of a planned outage. This would allow the permittee to continue operating and ensure better air quality for the community.
Comment No. 5. In the alternative, DEQ should require permittees to use Tier 4 controlled diesel generators.
Tier 2 emissions standards come up short on protecting public health. Tier 2 technology allows for massive amounts of harmful pollutants such as NOx, particulate matter, volatile organic compounds, and SO2. Diesel-fueled generation in particular can have acute localized effects—it can create “smog and exacerbate respiratory conditions, like asthma, chronic obstructive pulmonary disease, and lung cancer, especially for children and older adults.” Diesel Back-Up Generator Population Grows Rapidly in the Bay Area and Southern California, M.Cubed (2021), available at https://bit.ly/3LENog4. These localized problems occur because, unlike large generation sources, backup generators do not have tall smokestacks to disperse the pollutants far above the air that their neighbors breathe. Exacerbating the problem, “[d]iesel generators tend to be located close to where people live, work, and attend school.” Id.
Other technologies—like Tier 4 or Tier 2 with SCR—have more efficient controls that reduce emissions. As DEQ is well aware, SCR involves injecting ammonia into exhaust gas where it reacts with NOx to form nitrogen and water, decreasing NOx emissions substantially, while Tier 4 is a more stringent EPA standard introduced in 2004 for non-road diesel engines that reduces emissions limits for various air pollutants like NOx and particulate matter. 68 Fed. Reg. 38958 (June 29, 2024). The benefits of controlled diesel generators are evident in DEQ’s own Data Center Air Permit Guidelines. Tier 2 diesel generators emit ten times more NOx pollution than Tier 4 generators or Tier 2 generators with SCR.
If we are only talking about data centers, there are currently over 9,000 permitted diesel generators in Virginia, the vast majority of which are Tier 2 and located in Loudon County. See https://www.deq.virginia.gov/news-info/shortcuts/permits/air/issued-air-permits-for-data-centers. DEQs new interpretation would allow these 9.000 permitted diesel generators to run more frequently. Further, unlike many other areas in which diesel generators are common, the vast majority of diesel generators that would be covered by this “new interpretation” are clustered at data centers—facilities that are themselves clustered together in Loudoun County. Thus, these localized effects on health could be particularly acute for those who live, work, or go to school near these data centers.
DEQ should learn from California’s mistakes in allowing increased use of diesel generators. There, increasing wildfire-related outages have led many businesses and residents to rely more heavily on diesel backup. New Study Shows a Rapid Increase of Diesel-Fueled Backup Generators Across California, BusinessWire (October 6, 2021), available at https://bwnews.pr/3yVGc7L. For instance, two districts in California have the generator capacity to power about 15% of California’s grid. Research shows that this proliferation in diesel generators will cause $136 million in annual health costs, “due to increases in mortalities, heart attacks, hospital visits and other adverse consequences.” Id. Northern Virginia could see similar health costs if permittees are allowed to operate their generators more frequently during planned outages.
These concerns have led DEQ counterparts in other states to conclude that, “even if diesel engines operate relatively rarely on only the highest electricity demand days, their emissions on those specific days can be relatively significant and occur at the worst possible times for air pollution.” NESCAUM is a coalition of the state air quality agencies of Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont. Northeast States for Coordinated Air Use Management, About Us (accessed April 10, 2023), available at https://bit.ly/43qrjIW. Thus, although backup diesel generators have historically been exempt from strict “NOX and PM controls because of their limited use and relatively low total seasonal emissions,” that “rationale breaks down . . . when looking at the sources’ contributions on the most important smog-forming days as well as their expanding usage.” Id. DEQ’s failure to exhibit similar concern for the millions of Virginians under its charge is troubling.
CONCLUSION
For these reasons, DEQ should not change its interpretation of “sudden and reasonably unforeseeable.” To do so, would be to violate the APA by expanding the definition of “emergency” without going through the rulemaking process. Instead, if DEQ is concerned about permittees ability to operate during planned outages then, in recognition of its statutory directive to maintain and improve air quality, DEQ should require the installation of battery storage or the shifting or curtailing of load during those times. In the alternative, DEQ should require the use of Tier 4 controlled diesel generators.
Sierra Club appreciates the opportunity to comment on this Draft Permit.