Appeals Court Upholds EPA Approval of Phosphogypsum Road Test at Mosaic's Polk County Plant

A three-judge panel of the U.S. Court of Appeals for the Eleventh Circuit has unanimously rejected an environmental group's challenge to the Environmental Protection Agency's approval of a road-building test using phosphogypsum, a radioactive byproduct of fertilizer manufacturing, at a Mosaic Fertilizer facility in Polk County. The ruling was issued on August 12.

The Center for Biological Diversity had asked the court to vacate or send back the EPA's notice of approval, arguing that the decision violated the agency's own regulatory text or, alternatively, that it was arbitrary and capricious under the Administrative Procedure Act. The panel disagreed on both counts, holding that the EPA did not violate its regulations and that the agency's review and technical methodology were well supported, appropriately tailored and fully explained.

The decision leaves in place approval for Mosaic to use phosphogypsum in a road on its privately owned New Wales facility in Polk County. It is a test project on company property rather than a public highway, a distinction that has been central to how the EPA framed the approval.

What phosphogypsum is

Phosphogypsum is what remains after phosphate rock is processed into phosphoric acid for fertilizer. For every ton of phosphoric acid produced, the process generates roughly five tons of phosphogypsum. Florida, which holds a large share of U.S. phosphate reserves, has accumulated enormous quantities of it.

The material is stored in stacks, engineered piles that can rise hundreds of feet and cover hundreds of acres, with ponds of process water on top. Florida's landscape between Tampa and Lakeland includes several of these structures, and they are among the largest waste storage features in the state.

Phosphogypsum contains naturally occurring radioactive material concentrated from the original phosphate rock, principally radium, which decays into radon gas. That is the basis for federal regulation. EPA rules under the Clean Air Act generally prohibit removing phosphogypsum from stacks, with exceptions the agency can approve for specific uses on a case-by-case basis.

The regulatory history

The question of whether phosphogypsum can be used in road construction has moved back and forth across administrations. The EPA approved a road use request in 2020, then withdrew that approval in 2021 following legal challenge and further review. The agency later considered a narrower request from Mosaic tied to a specific test project on company-owned land.

That narrower framing is what the Eleventh Circuit evaluated. The approval at issue permits a demonstration road at the New Wales facility, allowing the company and regulators to gather data on the material's performance and on radiation exposure in a controlled setting rather than authorizing general use on public roads.

Separately, the Florida Legislature passed a 2023 law directing the state Department of Transportation to study phosphogypsum as a road base material, which reflected interest from the phosphate industry in finding a use for a material that currently has almost none.

What the court decided and what it did not

The panel's holding was narrow in an important way. The court evaluated whether the EPA followed its own regulations and whether the agency's technical reasoning was adequately supported and explained. It concluded that both were satisfied.

The court did not rule on whether phosphogypsum is safe as a road material in a general sense, and it did not authorize its use beyond the approved project. Judicial review of agency action under the Administrative Procedure Act asks whether the agency acted within its authority and reasoned adequately, not whether the agency reached the outcome a court would have chosen.

The Center for Biological Diversity has indicated that its broader campaign against expanded phosphogypsum use continues. Litigation over agency approvals typically produces a series of narrow rulings rather than a single resolution, and this one addressed one approval at one site.

The health question at the center of the dispute

The core scientific dispute concerns radon exposure. Radon is a radioactive gas produced by the decay of radium, and it is a recognized cause of lung cancer. Exposure risk depends on concentration and duration, which is why enclosed spaces are the primary concern in residential radon policy.

Environmental groups argue that placing phosphogypsum in roads distributes the material across the landscape, creates exposure pathways for construction workers and nearby residents, and complicates any future effort to control it. They also raise concerns about leaching into groundwater.

The EPA's approval rested on a technical evaluation of the specific project, including the depth of the material, the cover over it, the location on a controlled industrial site and the projected exposure to workers. The court found that evaluation adequately supported.

Why Florida has this problem

Florida's phosphate industry dates to the late nineteenth century, and the state remains a major producer. Bone Valley, the phosphate-rich region spanning parts of Polk, Hillsborough, Hardee, Manatee and DeSoto counties, has been mined for more than a century.

The industry supports thousands of jobs and contributes substantially to the economies of Polk and surrounding counties. It also generates a waste stream that the state has no established method for reducing, only for storing. Existing stacks continue to grow as production continues.

The Piney Point incident in Manatee County in 2021, when a failing stack at a closed fertilizer plant forced the release of hundreds of millions of gallons of contaminated water into Tampa Bay, made the storage risk vivid. That event was followed by a state-funded closure project and by a broader reassessment of how Florida manages legacy phosphogypsum sites.

What comes next for the material

The practical significance of the ruling is that a test project can proceed. Data from a demonstration road is what any future regulatory decision on broader use would be built on, and without it the debate would remain theoretical.

Whether that data leads to expanded approval is a separate question that would require additional EPA action and, almost certainly, additional litigation. The regulatory prohibition on removing phosphogypsum from stacks remains the default.

Industry interest is straightforward. A stack that can be drawn down rather than only added to changes the long-term liability picture for phosphate producers, and a road base material available in enormous quantity has obvious cost appeal for a state that builds a lot of roads.

Local impact in Polk County and Tampa Bay

Polk County sits at the center of Florida's phosphate region, and its residents live closest to both the benefits and the burdens. Mosaic is a significant local employer, and the county's economy has been tied to phosphate for generations.

The Tampa Bay watershed is the receiving environment for much of the region's surface water, which is why groundwater and stormwater concerns from phosphate operations extend well beyond the county line. The bay's recovery from decades of nutrient pollution is a long-running regional priority, and the Piney Point release set it back.

County commissions and municipal governments in the region have generally taken a cautious position on road applications, and several have adopted resolutions or public statements opposing use of the material on public roadways within their jurisdictions.

The broader environmental docket

The phosphogypsum ruling was one of several Florida-related decisions issued by the Eleventh Circuit in August. The same period produced rulings on federal railroad rulemaking involving Florida East Coast Railway and on a series of federal criminal appeals from Florida district courts.

The Eleventh Circuit, which covers Florida, Georgia and Alabama, is the federal appellate court that reviews most environmental agency decisions affecting Florida. Its rulings on EPA, Army Corps of Engineers and Fish and Wildlife Service actions carry weight across the region.

The court also ruled in April that the immigration detention facility built in the Everglades could continue operating despite not having undergone environmental review, a decision in a separate case brought in part by the same organization that challenged the phosphogypsum approval.

How much material Florida is storing

The scale of the problem is what makes the road question persistent. Estimates put the quantity of phosphogypsum stored in Florida stacks at well over a billion tons, accumulated across more than two dozen stack systems, some active and some closed. Each stack requires water management, groundwater monitoring and structural maintenance in perpetuity, and closed stacks do not stop generating obligations simply because production has ended.

Perpetual management is expensive, and it is not always funded. Piney Point in Manatee County became the cautionary example precisely because the responsible company had gone through bankruptcy, leaving the state to manage a deteriorating stack with process water it could not safely store. The 2021 emergency release into Tampa Bay, and the deep well injection project that followed, cost Florida taxpayers substantially.

That history shapes how local governments in the phosphate region evaluate any proposal involving the material. The concern is not only about radon exposure from a road surface but about whether creating a market for phosphogypsum changes the incentives around stack management, and whether the responsibility for material placed in roads would remain traceable decades later.

The federal framework that governs the decision

Phosphogypsum is regulated under the Clean Air Act through the National Emission Standards for Hazardous Air Pollutants, specifically the subpart addressing radon emissions from phosphogypsum stacks. The default rule requires that the material remain in stacks. The EPA retains authority to approve alternative uses when it determines that a proposed use is at least as protective of public health as stack storage.

That structure places the burden on the requesting party to demonstrate protectiveness for a specific application, and it makes each approval fact-specific. An approval for a demonstration road on a controlled industrial site does not establish that a public highway application would meet the same standard, because the exposure scenarios differ substantially in duration, proximity and the population involved.

It also means the litigation pattern is likely to repeat. Each new approval is separately reviewable, each review turns on the record the agency built for that application, and organizations opposing broader use have every incentive to challenge each one. The August 12 ruling resolves one round in what has been a multi-year sequence.

What's next

The Center for Biological Diversity could seek rehearing before the full Eleventh Circuit or petition the U.S. Supreme Court, though such petitions are rarely granted in cases turning on the adequacy of an agency's technical reasoning.

For the project itself, the next phase is construction and monitoring of the demonstration road at New Wales, with data collection that will inform any future regulatory proceeding.

For Floridians, the larger question the case raises remains unresolved. The state holds more than a billion tons of phosphogypsum in stacks that require perpetual management, and the debate over whether any beneficial use is acceptable will continue with or without this particular road.