xAI Southaven Gas Turbines: Mississippi Upholds 41-Unit, 1.2 GW Air Permit

After the two-day evidentiary hearing, the board "voted to deny the petitioners' appeal and request for relief," the Mississippi Department of Environmental Quality (MDEQ) said in a statement carried by WMC Action News 5, adding that the petitioners had not presented enough evidence for their claims and that the March permit stands. FOX13 Memphis, citing a release from the Southern Environmental Law Center (SELC), dates the vote to Tuesday, Nov. 10. Mississippi Today reported that the only dissent came from Agriculture Commissioner Andy Gipson, who said he had not received answers to all of his questions. The hearing was listed on the board's Nov. 10 agenda as a continuing evidentiary hearing on MZX.

Why it matters: the ruling settles, at agency level, the permit for permanent generation that supports xAI's data center operations. MDEQ's own record describes the plant as behind-the-meter, meaning none of its output is exported to the grid. xAI, which local outlets now call SpaceXAI, keeps the state air permit to construct 41 permanent turbines for continuous generation, while a federal lawsuit over the portable turbines already on the site goes on.

Simple-Cycle Turbines and Emission Controls

MZX Tech applied on Aug. 22, 2025 for a Prevention of Significant Deterioration (PSD) permit to construct 41 natural gas-fired, simple-cycle combustion turbines for continuous generation, with a capacity of 1.2 GW, according to the signed minutes of the board's March 10 meeting. Simple cycle means the hot exhaust is not reused to raise steam for a second generator, which trades efficiency for a simpler, faster build. A January report by DeSoto County News, citing MDEQ documents, lists the fleet as 17 Solar PGM-130, 16 Solar Titan 350 and eight ProEnergy 6000PE units; the sources give no per-model output, and the 1.2 GW is the site figure only.

The controls MDEQ set as best available control technology are a selective catalytic reduction system holding nitrogen oxides to 2 parts per million, an oxidation catalyst holding carbon monoxide to 4 ppm, and good combustion practice holding volatile organic compounds to 2.5 ppm, with pipeline-grade gas as the only fuel, the minutes show. The draft was tightened after comments to meet the updated federal turbine rule, KKKK, Jaricus Whitlock, chief of MDEQ's Air Division, told the board. No cooling towers or black-start engines are proposed, per the DeSoto County News report. Nothing in the sources shows the plant can island as a microgrid; it is on-site generation, not exported to the grid.

Who Owns and Pays for the Plant

No power purchase agreement or utility contract appears in the filings and reports Voltgrid read. The state paper at issue is a PSD permit to construct: it sets emission limits but is not a power contract, and it says nothing about how much of the campus's demand the plant covers. MZX Tech, which xAI representative Brent Mayo told the board in March is an xAI subsidiary, holds the permit and supplies xAI's own operations; xAI's Mayo called it support for a local Mississippi data center, and SELC, as cited by FOX13, says the plant supports operations in Memphis and Southaven, including Colossus 2. Mayo called the power plant and data center together the largest private investment in Mississippi's history, at more than $20 billion; that is the company's figure. The amount spent on the plant itself is not disclosed.

Permit Timeline and What Happens Next

The draft permit went to public notice from Jan. 16 to Feb. 17, 2026, drawing written comments from about 199 parties and spoken comments from 31 at the Feb. 17 hearing, according to the March minutes. The board approved permit No. 0680-00119 on March 10 with no recorded dissent. SELC appealed on April 9 for the NAACP, Young, Gifted & Green and the Safe and Sound Coalition, the NAACP said in a release.

At the November hearing SELC argued that MDEQ relied on limited modelling, did not require cleaner turbines and did not require emission offsets, Mississippi Today reported. The offsets dispute turns on air quality. MDEQ told the board in March that DeSoto County is in attainment with every national standard, so the offset rule does not apply; SELC says the Memphis area fails the federal smog standard and that offsets are required anyway. Trudy Fisher, a former MDEQ executive director arguing for MZX Tech, said the agency modelled the turbines extensively and consulted the U.S. Environmental Protection Agency.

Under MDEQ's process, parties aggrieved by the board's final decision can seek review in chancery court. The next things to watch are whether the petitioners file there, and the ruling on the NAACP's request for a preliminary injunction in federal court, which is still pending. The board next meets on Dec. 8.

What On-Site Gas Means for Data Centers

The case shows the two tracks on-site gas runs on. The permanent plant now has its state permit upheld. The 27 portable turbines on the site are a separate matter: MDEQ told the board in March they were exempt "mobile sources" and not part of the permit. On Oct. 30 a federal court denied xAI's motion to dismiss the NAACP's Clean Air Act suit, finding, according to plaintiffs' counsel, that the plant is not a mobile source. Around the site, xAI's unit has been offering to buy nearby homes in return for a release of claims, and a recording put the target at 418 homes.

For scale, Southaven's stated 1.2 GW of generating capacity compares with 366 MW of plant capacity at El Paso Electric's McCloud plant for Meta, which the utility plans as bridge power islanded from the grid. No source states the Colossus 2 load in megawatts, so how much of the campus's demand the plant covers is unknown.

What Is Not Confirmed Yet

The board's written decision, the November minutes, the final permit and its statement of basis were not available to Voltgrid; the board approves each meeting's minutes at the next one, which is set for Dec. 8. The wording of MDEQ's Nov. 10 statement comes from WMC Action News 5 alone, and Gipson's dissent from Mississippi Today alone. The permit's annual emission limits and operating-hour caps are not confirmed. Whether the eight converted jet-engine turbines reported on Nov. 4 are the eight permitted ProEnergy units is not stated by any source. No statement from xAI on the ruling appeared in the reports Voltgrid read.