Tampa-based Mosaic is asking for federal approval to expand a waste pile in Riverview by nearly 180 acres.
The company is seeking a Clean Water Act permit from the U.S. Army Corps of Engineers to fill a group of waterways west of its facility to complete the expansion.
The pile contains phosphogypsum, a radioactive compound required by regulation to be contained in special stacks to prevent exposure.
Mosaic officials say expanding the existing stack would extend its life by about 16 years.
But environmental groups have raised concerns, citing the 2021 Piney Point disaster in Manatee County, where more than 200 million gallons of contaminated water had to be pumped into Tampa Bay after a leak was discovered at the facility.
Tampa Bay Waterkeeper executive director Justin Tramble said a spill could even have an economic impact on the region.
“Water quality is the leading industry in Tampa Bay,” he said. “The marine life, the seagrass, the mangroves, all of that obviously has a significant amount of ecological value, which turns into economic value.
"215 million gallons of the waste from the stacks was released into the Tampa Bay estuary and caused one of the worst fish kills that Tampa Bay has ever seen."
In 2025, a coalition of environmental organizations filed suit against the federal government over the lack of regulation of radioactive waste from fertilizer production.
Despite this, Mosaic is moving forward with the permitting process across multiple levels of county, state and federal government.
“The federal government doesn’t elevate phosphogypsum to the thresholds of other toxic chemicals,” Tramble pointed out. “We understand the need for this industry; what we don’t understand is fast-tracking a permit like this, and we’re concerned that certain industries get priority over the number one industry in the state, which is our clean water.”
As required by law, Mosaic intends to offset potential environmental impacts by purchasing mitigation credits to restore other natural habitats.
“In addition to performing mitigation, Mosaic has offered to Hillsborough County to protect more than 300 acres of bayfront property located between the Alafia River and Bullfrog Creek,” Mosaic’s external communications manager, Chloe Conboy Renard, said in a statement. “This area contains valuable habitats, including mangroves, salterns, and upland hardwood forest. Given its unique location, existing access and nearby utilities, this area could be subject to development pressure if it remains unprotected. It is one of the few remaining natural areas along Hillsborough Bay.”
If approved, the expansion would begin in 2028 and last about 2.5 years.
The Army Corps opened up a public comment period that spanned from Feb. 17 to March 19.
It received more than 150 comments covering the following concerns:
Water Quality
- Public comments express concern that expanding the phosphogypsum stack would increase the risk of leaks, spills, or structural failures that contaminate Tampa Bay, Hillsborough Bay, the Alafia River, North Archie Creek, and the Floridan Aquifer, which supplies drinking water to millions.
- Commenters emphasize that phosphogypsum process water contains radioactive and toxic constituents (including radium and heavy metals), and express concern for irreversible long‑term groundwater contamination.
Fish and Wildlife
- Many comments express concern for filling tidal mangrove wetlands and creek headwaters that serve as nursery habitat for fish such as snook, tarpon, red drum, and trout.
- Commenters express concern for potential risks to protected species, including West Indian manatees, sea turtles, smalltooth sawfish, wood storks, and eastern indigo snakes, and urge extreme caution in altering habitat connected to the Tampa Bay estuary.
Wetlands & Aquatic Resources
- Commenters express concern that proposed impacts will affect wetlands and mangroves which provide natural flood storage, shoreline protection, and water‑quality filtration for the bay, and question if functions can be adequately replaced through mitigation credits.
- Commenters suggest converting wetlands to industrial waste storage is inconsistent with long‑term protection of coastal ecosystems and undermines decades of restoration work in Tampa Bay.
Flood Hazards & Storm Risk
- Commenters repeatedly note that the proposed expansion area is less than a mile from Tampa Bay and near the Alafia River in a low‑lying, surge‑prone zone.
- Commenters cite recent severe hurricanes and flooding in 2024 as evidence that storm surge, extreme rainfall, or future sinkholes could breach or destabilize the stack, creating a public safety risk.
Public Health and Safety
- Many comments characterize phosphogypsum as a toxic, radioactive waste that can emit radon and carry carcinogens and heavy metals, asserting links to cancer and respiratory illness in communities near existing stacks.
- Commenters suggest expanding near densely populated areas exposes residents, including children, to unacceptable risks from airborne particulates, contaminated water, and potential disaster scenarios.
Economics & Property Interests
- Local residents and nearby businesses suggest the project could reduce property values, deter customers, and increase costs for insurance and operations due to perceived health and safety risks.
- Commenters suggest Tampa Bay’s tourism, recreation, and fishing economy depends on clean water and healthy ecosystems, and that a major spill or chronic pollution from the proposed project would impose significant long‑term economic costs on the region.
Recreation
- Commenters suggest the project may degrade water quality or leak pollutants resulting in fish kills which could directly affect recreational activities (boating, fishing, and other water sports) in Tampa Bay and its tributaries.
- Fishing guides and local users specifically identify Archie Creek headwaters and nearby estuarine habitats as important recreational and ecological areas which should be protected from industrial encroachment.
General Environmental Concerns / Conservation / Cumulative Impacts
- Many commenters reference Mosaic’s past spills, sinkholes, and enforcement actions, suggesting historic pollution and cumulative impacts make expansion at the site unacceptable.
- Commenters suggest consideration of alternative waste management technologies and relocating waste storage facilities away from sensitive coastal and aquifer areas.
- Commenters request updated storm‑surge and climate‑risk analyses for phosphogypsum stacks.
- Commenters request regulatory scrutiny to ensure that long‑term public and environmental interests are prioritized over short‑term industrial expansion.
