Alabama Caps Data Center Diesel Engine Hours
Proposed permits limit 42 backup engines at the Columbiana site to 90 hours per year, keeping emissions below major-source thresholds.
Updated on Nov. 2, 2026 in Data Centers
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The Alabama Department of Environmental Management (ADEM) has proposed draft synthetic minor air permits for 42 diesel engines at Digi Power X's planned Columbiana data center, capping each engine at 90 hours of operation per rolling 12 months. The permits are proposed, not final, and ADEM has set no date for a decision after the public comment period.
Why it matters
Backup diesel generators at large data centers are a growing permitting pressure point as AI campuses scale, and the proposed hour caps are designed to keep the facility below major-source emissions thresholds. The Columbiana project is tied to a 40 megawatt campus for Cerebras Systems under a $1.1 billion colocation agreement, which makes the permit terms a test of how Alabama handles this class of facility.
ADEM's engineering analysis puts potential annual emissions at 93.46 tons of nitrogen oxides and 36.91 tons of carbon monoxide, both under the 100-ton Title V major source threshold. The proposed draft caps each of the 42 engines at 90 hours per rolling 12 months, while the engines range from 1,490 to 3,640 brake horsepower and diesel is limited to 15 parts per million sulfur.
The players
Alabama Department of Environmental Management (ADEM)
The state environmental agency that proposed the draft air permits and will decide them after the public comment period.
Digi Power X
The company developing the Columbiana data center campus, whose on-site substation is built and whose power delivery agreement with Alabama Power is signed.
Cerebras Systems
The AI chipmaker tied to a 40 megawatt campus at the site under a $1.1 billion colocation agreement described in Digi Power X's May 2026 SEC filing.
The details
The draft permits are synthetic minor permits, meaning enforceable operating limits keep a facility's potential emissions below the level that would classify it as a major source. Proviso 22 caps total operation at 90 hours per engine with no emergency exception, while Proviso 27 allows unlimited emergency use plus up to 100 hours a year for maintenance and readiness testing. Operators must total each engine's hours monthly on non-resettable meters and log every run as emergency or non-emergency. ADEM requires no stack testing, and operators must report any overrun within two working days.
Timeline
May 8, 2026: Digi Power X applied for the air permits.
October 13, 2026: ADEM walked the greenfield site.
October 29, 2026: ADEM proposed the draft synthetic minor permits.
December 15: The company's first 15 megawatts are due.
The Tech Race
The Columbiana permits follow the pattern of data center developers using operating-hour caps on backup diesel generators to stay under the 100-ton Title V threshold of the Clean Air Act. The 40 megawatt Cerebras campus tied to the same site shows how AI chip demand is driving capacity into smaller state-permitted facilities.
Residents near the Columbiana site may see the backup engines run only within the proposed hour caps, with any overrun reported to ADEM within two working days. Anyone in Shelby County can submit comments or request a hearing within the 15-day window after publication.
The takeaway
Watch for whether ADEM finalizes the 90-hour caps unchanged after comments and whether Digi Power X meets its first 15 megawatt delivery due December 15. Those two milestones will show whether synthetic minor permits can hold for AI-scale backup generation.
What happens next
ADEM will review public comments and any hearing requests received within 15 days after publication before issuing a final permit decision, which has no date set.
Further reading
For broader context on how AI campuses are reshaping grid and infrastructure planning, see Data Centers coverage across Alabama.
Source note: This article includes information reported by Environment+Energy Leader.
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