Why are data-center
generators running in Ashburn?

The honest short answer is: the sight or sound of generators does not reveal why they are running. A permit may state several authorized purposes and different hour limits. A particular event requires a facility identity, time, permit and operating records.

What to check in the air permit

1. Facility and permit number. A road location or company name may point to several buildings or permits.
2. Equipment reference. Match the document-defined generator group rather than assuming every unit has the same terms.
3. Operating basis. Look for per-unit versus combined limits, rolling periods, maintenance/testing language and separately defined non-emergency use.
4. Controls and pollutant limits. Preserve whether a row is controlled or uncontrolled and whether the limit is hourly, annual, visible-emission, combined or per unit.
5. Document history. An amended or superseding permit can change the relevant conditions.

Release 2 publishes those page-cited fields for 16 Loudoun County permit documents with a visible QA tier on every profile. Machine-extracted candidates must be checked against the linked PDF before reuse. The tables are not an assertion about a particular generator event.

Do the 2026 Tier 4-equivalent rules apply?

Virginia DEQ says revised guidance APG-576 became effective April 9, 2026. The agency describes presumptive controls based on selective catalytic reduction or equivalent nitrogen-oxide control, a diesel oxidation catalyst or equivalent carbon-monoxide control and a diesel particulate filter or equivalent particulate-matter control.

DEQ states that the updated requirements apply to data-center diesel-generator permit applications received on or after July 1, 2026. That makes the application-received date—not merely the permit issuance date—the key field to check.

DEQ also distinguishes emergency from non-emergency generation. The agency says a generator used for demand-side distribution or when a utility asks for extra capacity is not emergency generation. The controlling permit determines what is authorized for a named facility.

What does visible yellow or orange exhaust prove?

A photograph or video can preserve a visible condition and, when documented carefully, its location and time. It cannot by itself identify a pollutant, concentration, operating purpose, permit condition, compliance status or health effect.

Useful follow-up evidence can include the precise observation time, direction of view, nearby address or facility identifier, weather conditions, the applicable permit, DEQ response and operational or testing records obtained from the appropriate source.

How to document and report an observation

• Record when the event began and ended, or state that duration is unknown.
• Record the observation location and direction without entering private property.
• Preserve the original photo or video and avoid editing that removes time or location context.
• Describe color, odor and sound as observations, not pollutant identification.
• Use Virginia DEQ’s Pollution Data and Reporting process for a suspected pollution incident.
• For an imminent threat to health or the environment, follow DEQ’s instruction to contact local 911 and the Virginia Emergency Operations Center.

Page-cited Loudoun permit terms

These are the newest Loudoun County documents in Permit Document Enrichment — Release 2. Open the profile for equipment, operating-scope and pollutant-limit rows, PDF page links and the document’s QA tier.

Common questions