The Colorado Air Pollution Control Division (APCD) alleges that QTS, a major data center developer, proceeded with construction on two additional data centers at its east Aurora campus before receiving state approval to install 98 new diesel backup generators. The agency issued the notice following inspections this summer and fall.

"It is important that companies apply for, and await approval of, these permits so that the state can ensure any additional emissions comply with state and federal air pollution standards," Leah Schleifer, an APCD spokesperson, said in an email.

The dispute centers on a permit modification QTS requested in June 2025. The company already held a construction permit, issued in March 2025, for 40 backup generators associated with its first data center. It sought a "minor modification" to add two more data centers and 98 additional diesel generators. That modification has not been approved.

According to APCD, a state inspector visited the site in July and observed that QTS had nearly completed the exterior of the second data center without a valid construction permit. The inspector sent a report to QTS in August. During a follow-up inspection in September, the inspector found the exterior of the second building appeared complete and construction had begun on a third data center.

"QTS needed a construction permit before it began constructing an addition to its data center, which will involve the installation of additional emergency generator engines," Schleifer said.

State regulators also cited the company for failing to comply with permits for its existing generators.

QTS maintains it has followed the rules. A company spokesperson said QTS has "secured the entitlements and permits necessary to begin construction activities currently underway" and is "working collaboratively" with APCD on the violation.

Aurora officials said local building permits were properly issued. QTS received city construction permits for its first building in 2022 and for newer buildings as recently as July 2026.

"From the perspective of our building division, no construction has been performed without the required plan review approvals, permit issuance and inspections," Aurora spokesperson Joe Rubino said in an email.

QTS did not answer questions about whether the 98 backup generators are currently on site, why it proceeded with construction, or whether it disputes the state's findings.

The notice of violation is likely to intensify an already heated debate in Aurora, where the city council has faced contentious public hearings over proposed moratoriums on data centers and may soon consider banning tax incentives for them. Mayor Mike Coffman declined to comment but said during a council meeting Monday night that he would try to reintroduce a moratorium at the next meeting. Such a moratorium, however, may not affect QTS because its project is well underway, and it would not apply to the separate 500-megawatt Trident project, which is on track to become the largest data center in the state.

The QTS campus is projected to consume nearly four times as much electricity as Denver International Airport uses at peak demand. Its diesel generators, intended for backup power during grid overloads or blackouts, have become a focal point for air quality scientists and project critics. QTS has said the generators would be used only for limited testing, maintenance and emergency events, similar to hospital backup generators.

But even infrequent use poses significant health risks. A Washington Post analysis of air quality permits for more than 132 data centers in Virginia, which have more than 10,000 generators combined, found that operating them less than an average of an hour per week would carry roughly the same public health risks as five large gas-fired power plants.

QTS estimates that the additional generators at its Aurora site could triple its particulate matter emissions and double its nitrogen oxide emissions — key ingredients in Colorado's summertime ozone struggles. This summer was one of the worst for air quality along the Front Range, according to data from the Regional Air Quality Council. Ozone pollution can lead to serious health issues, including heart attacks and asthma.

The full scope of penalties QTS may face — whether fines or a stop-work order — remains unclear. APCD is expected to open a public comment period on the company's modified permit before the end of the year.