EPA Moving To Regulate Some Data Center Turbines As ‘Mobile Sources’

• By: AWMA
• On: 04/01/2026 17:56:59
• In: Press
• Comments: 0

At a March 24 conference hosted by the Air and Waste Management Association (AWMA) in Herndon, VA, environmental regulators gathered to discuss the challenges of data centers for energy consumption, air pollution, water use, noise and other issues.

In air regulation, a central theme of the event was the burden imposed by the new source review (NSR) permitting program, especially where a single power generation source or a group of smaller sources together qualify as a “major source.” Developers typically seek to avoid their temporary power sources being classed as such, to speed the permitting process and avoid tougher permit requirements, several speakers noted.

But if EPA were to allow truck-mounted turbines or engines to be deemed “mobile sources,” this would side-step developers' air permitting problems.
EPA hinted at this strategy in its revised January new source performance standards (NSPS) for combustion turbines of many types, which walked back Biden-era proposed tougher limits. There, the agency created a special, less-stringent nitrogen oxides (NOx) requirement for “temporary” power sources.

Further, EPA said it is “including a conditional exclusion” in its NSPS regulation “that will exclude combustion turbines from the definition of ‘stationary combustion turbine,' if the turbine meets the definition of ‘nonroad engine' under title II of the Act and applicable regulations, and is certified to meet emission standards promulgated pursuant to title II of the Act, along with all related requirements.”
“This provision will become operative if the EPA in the future adopts nonroad emission standards and certification requirements for portable combustion turbines” -- a move that is now expected to proceed.

Meanwhile, EPA has sent for White House interagency review its proposal to allow a more flexible interpretation of “begin actual construction” in the context of NSR. While NSR does not allow construction of a source without the necessary permit in hand first, the rule is expected to allow project developers to build certain elements of a plant, such as a foundation or a roof, so long as no “emissions unit” is installed. EPA has already taken this approach in guidance to Arizona air regulators, but the forthcoming rule would codify the changes.
It is not clear whether the draft proposal undergoing White House review might also address the planned nonroad emission standards for “portable” turbines.

Temporary Power Sources
Permitting temporary power sources has become a contentious issue at some data centers, such as the sites owned by Elon Musk's xAI in Tennessee and Mississippi, which support the Grok artificial intelligence (AI) platform.

In one ongoing dispute, environmentalists are threatening legal action over unpermitted “temporary” combustion turbines in Mississippi used to power a data center in neighboring Tennessee. At another site, xAI did seek a major source permit for a similar arrangement after local complaints.
Congressional Democrats are pressing AI companies including xAI, OpenAI and Meta about the environmental effects of their facilities, including pollution from large gas turbines planned to provide on-site power.

And New York Gov. Kathy Hochul (D) has launched a regulatory process to determine environmental and other requirements for data centers and AI infrastructure, an approach that contrasts with calls from President Trump and Republicans for voluntary approaches for the booming industry.
But EPA in its forthcoming rule may enable project developers to sidestep the issue of stationary source permitting entirely, by instead allowing truck-mounted temporary power sources to be regulated as mobile sources, subject to the different regulatory requirements of Clean Air Act Title II.
Stationary sources are subject to NSPS. In addition, major stationary sources are subject to best available control technology (BACT), a stringent, case-specific level of emissions control under prevention of significant deterioration (PSD), the NSR program that applies in areas meeting national ambient air quality standards (NAAQS).

In areas violating the NAAQS, nonattainment NSR applies, with even tougher requirements such as pollution offsets. In many areas that were previously in nonattainment, such as much of Maryland, the air law's anti-backsliding provisions require that tough PSD permit conditions -- such as lower emissions thresholds to be considered a “major source” -- still apply, noted Suma Sariscak, manager of the air quality permits program at the Maryland Department of the Environment, during the AWMA conference.

Developers thus seek where possible to obtain “minor source” status, often by voluntarily limiting their projects' potential to emit (PTE) and becoming a “synthetic minor” source. Minor source permits are not as stringent and are faster to obtain, noted speakers including Robert Velasco, an environmental expert with the Tampa Electric Company, and Lori Madrid, a consultant with engineering and professional services firm WSP.
When a power source or collection of sources is located in one site, and the data center it serves is located in another, this raises questions of “aggregation,” or whether multiple sources should be treated as one for the purposes of NSR. Aggregating multiple sources increases the chance that collectively, they will be considered a single major source. Madrid noted that at “hyperscale” data centers, it is not unusual to see anywhere from 50 to 150 diesel generators, which taken together can constitute a major source.

EPA and local air regulators weigh factors such as common ownership, geographical proximity and whether most or all of the power produced serves to power the primary facility -- here, the data center -- when deciding whether to aggregate.
Such discussions are increasingly frequent amid surging demand for power to data centers, concerns over power supplies, prices, environmental and aesthetic issues among local residents close to data centers, and also political pushback against data center construction from environmentalists and Democrats.

Speakers at the AWMA event noted that future trends in data center power sources may include natural gas fuel cells, battery storage, and even small modular nuclear reactors.
To speed permitting of data centers in general, EPA has already taken steps such as reinstating policies from the first Trump administration on not “second guessing” states' NSR determinations, such as where sources are minor or major, and also allowing project developers to count emissions decreases, as well as increases, at the initial stage of NSR.

House Republicans are also looking to advance a series of bills that would ease Clean Air Act requirements, including NSR permitting. -- Stuart Parker (sparker@iwpnews.com)
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