Virginia: Tier 4-equivalent emissions now required by statute for data center gen-sets

Status: In effect · Applies to: applications submitted on or after 1 July 2026

What changed

Virginia wrote a data center-specific emissions requirement into statute. It is not agency guidance that DEQ could revise on its own — it is § 10.1-1322.6, enacted as HB 507 in the 2026 session.

Who it applies to

Data center air permit applications submitted to DEQ on or after 1 July 2026.

Two things worth knowing about the edges.

Applications submitted before that date are not covered. And the statute does not itself create a permit requirement — it governs permits that are already required, where the application is submitted on or after 1 July 2026. A project that needs no air permit is outside it.

On exemptions: Virginia’s minor NSR permit exemptions list, among other categories, diesel engines with an aggregate rated brake horsepower of less than 1,675, and diesel engines powering electrical generators with an aggregate rated electrical output of less than 1,125 kW — in each case subject to the regulation’s other conditions. A project above those size thresholds is not automatically outside the exemptions: the regulation also provides a separate route that turns on uncontrolled emission rates rather than size, with its own conditions. Neither route is automatic, and which applies depends on the application.

What the law actually requires

DEQ cannot issue the permit unless the emission limit established for each gen-set under that permit is equal to or lower than the emissions achieved by a Tier 4-equivalent gen-set.

That is a performance standard, not an equipment mandate. The statute defines Tier 4 equivalent by reference to three controls — selective catalytic reduction or equivalent for NOx, a diesel oxidation catalyst or equivalent for carbon monoxide, and a diesel particulate filter or equivalent for particulate matter. The phrase “or equivalent” appears in each.

The statute itself does not use the term BACT. Separately, DEQ Guidance Memo APG-576, whose revised version took effect 9 April 2026, addresses presumptive best available control technology for emergency and non-emergency diesel engine-generator sets at data center stationary sources. The statute sets the permit limit; DEQ’s guidance addresses presumptive BACT for these generator sets.

Why an enterprise data center owner should care

For applications covered by the statute, Tier 4-equivalent performance is now a statutory minimum for control stringency. DEQ can still establish more stringent emission limits through the applicable permitting process — BACT, LAER or other requirements still apply.

One practical implication: emissions performance can now be screened during equipment selection, because a permit covered by the statute cannot establish a gen-set limit above the Tier 4-equivalent benchmark. That is our read of what the requirement means in practice, not something the statute states.

What we can and cannot conclude yet

We have verified what the statute says, what it defines, when it applies, and the existence of both the size-based exemption and an additional emissions-based exemption pathway.

We have not established what it costs. Aftertreatment systems plausibly affect equipment price, physical footprint and procurement lead time, but we have found no verified source quantifying any of those effects for Virginia data center projects specifically. DCU will not publish estimates it cannot support.

The statute applies to an application submitted on or after 1 July 2026, but it does not expressly address how that date applies to amendment or modification requests involving permits issued earlier. DCU has not found published DEQ guidance resolving that question.

Both are open questions we are working on.

← All regulatory items