April 8, 2026

Stanley Faggert 

Air and Renewable Energy Division 

Virginia Department of Environmental Quality 

1111 E. Main Street, Suite 1400 

Richmond, VA 23219

Re: Diesel Engine-Generator Set Procedure for Writing New and Modified Permits – DEQ Guidance Memo APG-576

Dear Mr. Faggert:

On behalf of the Sierra Club Virginia Chapter, we write to express our strong support with caveats for the Department of Environmental Quality's proposed revision to DEQ Guidance Memo APG-576. The Sierra Club Virginia Chapter urges DEQ to finalize and rigorously implement this revision, which represents a critical step toward protecting the health of Virginia's communities — especially those already bearing a disproportionate burden of air pollution — from the growing environmental threat posed by data center diesel generator emissions.

The Sierra Club is the nation's oldest and largest grassroots environmental organization, with more than 3.8 million members and supporters nationwide. The Sierra Club Virginia Chapter has long championed clean air, public health, and environmental justice across the Commonwealth. 

Air Pollution and Community Health: The Urgent Case for Action

The Sierra Club's foremost concern regarding data center diesel generators is their direct impact on air quality and community health. These facilities routinely rely on diesel generators and the emissions they produce carry serious public health consequences.

Diesel exhaust is a toxic mixture containing harmful concentrations of particulate matter (PM2.5), nitrogen oxides (NOx), sulfur dioxide (SO?), and carbon dioxide (CO?). These pollutants do not stay at the facility fence line — they travel into surrounding neighborhoods, schools, and homes, with particularly acute effects on:

• Children, whose developing lungs are especially vulnerable to particulate matter and ozone formed by NOx emissions;

• Older adults, who face heightened risk of cardiovascular and respiratory complications from diesel exhaust exposure;

• Individuals with pre-existing conditions such as asthma, COPD, or heart disease, for whom diesel pollution can trigger acute health crises; and

• Environmental justice communities — often lower-income and communities of color — that already bear disproportionate pollution burdens and are frequently located in close proximity to industrial development.

Research has firmly established that diesel exhaust exposure contributes to the development and aggravation of chronic conditions including asthma and other respiratory diseases, cardiovascular disease, and premature death. 

Beyond direct health harms, diesel exhaust exacerbates climate change, contributes to acid rain, and degrades regional air quality through smog formation — impacts that fall hardest on those with the least capacity to protect themselves.

This Guidance Memo represents an important first regulatory response to these documented harms. The Sierra Club strongly supports measures that meaningfully reduce diesel exhaust emissions from data center operations, and we urge DEQ to treat this rule as a baseline — not a ceiling — for future protective action.

APG-578 and the Expanded Use of Emergency Generators

The urgency of the Guidance Memo is compounded by recent changes to DEQ's related Guidance Memo APG-578. As of December 2025, APG-578 broadly interprets the definition of "emergency" under the Virginia Administrative Code, permitting facilities to operate backup generators during planned electrical outages — events for which facilities may have had up to fourteen days' advance notice.

The Sierra Club has serious concerns about this interpretation. The Virginia Administrative Code requires that an "emergency" be "reasonably unforeseeable." Permitting diesel generators to run during knowingly planned outages stretches this definition beyond its plain meaning and, critically, significantly increases the total hours of diesel exhaust exposure for communities surrounding data centers. More frequent generator operation means more pollution, more health impacts, and greater cumulative harm to communities.

In this context, APG-576's requirement that generators meet Tier 4 equivalence — for both emergency and non-emergency use — is essential. If generators will run more frequently, including during events that are plainly not emergencies, then the strictest available pollution controls must apply. The Sierra Club fully endorses this approach.

Zooming out, Sierra Club is deeply concerned about the scope of and reliance on “non-emergency” generators and believes this guidance inadequately addresses the potential impacts of generators that lack constraints. These generators have historically been installed to meet emergency back-up functions, and not to serve as primary power or to invite more intense usage. We urge the Department of Environmental Quality to issue further guidance that accomplishes the following:  

1. Specificity in guidance about how and when generators can be used by placing 500 hour limits on all diesel generators.

2. Public notification when generators run for 4 or more hours. 

   1. The public, and especially those residents compromised by conditions that can be exacerbated by diesel pollution and emissions, need to know when particulate matter (PM2.5), nitrogen oxides (NOx), sulfur dioxide (SO?), and carbon dioxide (CO?) levels may be elevated. 

   2. Special notification standards should be developed to notify infant or early childhood daycares, preschools, elementary schools, secondary schools, hospitals and senior centers or living facilities.

3. The Department of Environmental Quality should define “cumulative impact.” 

   1. In areas where data centers are clustered and where cumulative emissions and pollutants can be far greater than the limits of one stand-alone permit, impacted communities are experiencing “cumulative impacts.” Air quality permits should consider “cumulative impact” on both local ecology and communities.    

Tier 4 Generators as Best Available Control Technology

The Guidance Memo appropriately designates Tier 4-equivalent generators as Best Available Control Technology ("BACT") for new data center stationary sources. The Virginia Administrative Code defines BACT as an emissions limitation based on the maximum degree of emission reduction achievable through the application of available methods, systems, and techniques, taking into account energy, environmental, and economic impacts. The Air Pollution Control Board is further instructed to consider the nature and amount of emissions, control efficiencies achieved in the industry, and total cost effectiveness.

Tier 4-equivalent generators satisfy each of these criteria:

• Emissions reductions: Tier 4 generators emit approximately 90% fewer pollutants than lower-tier alternatives, dramatically reducing nitrogen oxide, particulate matter, and other harmful emissions.

• Technological availability: Tier 4 generators incorporating selective catalytic reduction systems, diesel oxidation catalysts, and diesel particulate filters are commercially available and widely deployed in the data center industry.

• Cost effectiveness: The Guidance Memo establishes a rigorous standard for bypassing the Tier 4 presumption, requiring applicants to demonstrate site-specific factors of such uniqueness that the associated costs are substantially greater than those for the broader source category. Merely citing high costs will not suffice. This framework appropriately places the burden on industry to justify any deviation.

The Sierra Club firmly agrees with DEQ's determination that Tier 4-equivalent technology represents BACT for data center generators. The public health and environmental benefits of this designation far outweigh the incremental compliance costs for an industry known for its substantial capital investment.

H.B. 507 and the Importance of Regulatory Alignment

The Guidance Memo complements H.B. 507, which passed both chambers of the 2026 Virginia General Assembly and currently awaits Governor Spanberger's signature. H.B. 507 would amend the Code of Virginia to require that data center permits issued after July 1, 2026, reflect emission limits at or below those achievable by a Tier 4 generator.

By defining presumptive BACT for data centers to include the use of selective catalytic reduction systems, diesel oxidation catalysts, and diesel particulate filters, the Guidance Memo operationalizes the legislative intent behind H.B. 507. This alignment of regulatory guidance with statutory direction reflects sound policy and ensures that the Commonwealth's environmental commitments are implemented consistently and effectively.

The Sierra Club strongly encourages DEQ to finalize the Guidance Memo promptly and to ensure its effective enforcement so that data centers receiving permits on or after July 1, 2026, are held to the Tier 4-equivalent standard in both letter and spirit.

Virginians deserve to breathe clean air. As data centers multiply across the Commonwealth, the cumulative pollution burden on surrounding communities will only grow unless strong, enforceable standards are in place. Guidance Memo APG-576 is exactly the kind of protective action DEQ must take to meet its obligation to safeguard public health and the environment. 

Respectfully submitted,

Corrina Beall, Legislative and Political Director 

Sierra Club Virginia Chapter