Mining giant Mosaic seeks federal approval to expand its waste pile near Tampa Bay
Mining giant Mosaic seeks federal approval to expand its waste pile near Tampa Bay
Some environmental groups, including climate education nonprofit The CLEO Institute, have raised concerns about extending Mosaic’s wide-scale industrial facility closer to Tampa Bay’s coast in an area that’s vulnerable to storm surge and flooding.
Max Chesnes
A public comment period runs until March 19 on Mosaic’s proposal to increase its “gypstack” in Hillsborough County.
Running out of room to store its phosphate waste, Tampa fertilizer giant Mosaic is seeking permission from federal environmental regulators to expand its waste pile near the shores of Tampa Bay.
The Fortune 500 company wants to widen its Riverview phosphogypsum stack by nearly 180 acres, an expansion the company estimates would extend the life of its Hillsborough County plant by 16 years.
To do that, the company is asking the U.S. Army Corps of Engineers for a Clean Water Act permit to fill roughly 35 acres of wetlands, ponds, ditches and other water bodies to the west of its plant. Mosaic estimates it would take about 305,000 cubic yards of material — enough to fill roughly 100 Olympic-size swimming pools — to create solid ground for the expansion.
Mosaic says its Riverview plant has six years of storage remaining for its phosphogypsum, a solid waste created in fertilizer manufacturing that contains radium, which decays to form radon gas.
In an effort to reduce the public’s exposure, federal regulators require companies like Mosaic to store their phosphogypsum in engineered “gypstacks” because both radium and radon are radioactive and can cause cancer.
The waste piles are hard to miss: Mosaic’s Riverview stack is hundreds of feet tall — sometimes mistaken for a landfill — and can be seen from nearby U.S. Highway 41 and from boats cruising Hillsborough Bay.
Most of the land in Riverview that Mosaic wants to build upon is largely industrial and home to mineral processing, an automobile salvage yard and two former racing facilities. In 2024, Mosaic bought the former East Bay Raceway park for its proposed expansion, property records show.
Some environmental groups, including climate education nonprofit The CLEO Institute, have raised concerns about extending Mosaic’s wide-scale industrial facility closer to Tampa Bay’s coast in an area that’s vulnerable to storm surge and flooding. According to the Corps permit review, the land Mosaic wants to build on is less than a mile from Tampa Bay and about a mile north of the Alafia River.
Because of the sweeping scale of the project, the company is moving through the permitting process across multiple levels of county, state and federal government. In January, Mosaic applied for a wetland impact permit with the Environmental Protection Commission of Hillsborough County, which is still under review, according to officials with its wetlands division.
As Mosaic moves forward with permitting, “it’s clear that this expansion is moving full steam ahead,” said Elise Bennett, the Florida and Caribbean director at the nonprofit Center for Biological Diversity. The group has sued the Trump administration over what it claims is a failure to regulate phosphate mining waste.
The proposed expansion is also the first manufacturing project that qualifies for a federal program, called FAST-41, designed to streamline the complex permitting process for large-scale infrastructure projects.
“It’s outrageous that the Trump administration is fast-tracking this request to dump even more toxic waste so close to Tampa Bay,” Bennett said in a statement. She said Tampa Bay residents are familiar with the threats posed by the phosphate industry, invoking the 2021 Piney Point wastewater disaster that dumped 215 million gallons of polluted water into Tampa Bay. The site owners in that case were HRK Holdings, not Mosaic.
State data shows Mosaic owns and operates two-thirds of Florida’s 25 active and closed stacks, most of which are in a phosphate-rich region east of Tampa called Bone Valley.
If all of the regulatory milestones are cleared, Mosaic estimates construction on the expanded gypstack would begin in January 2028 and last about 2½ years.
Mosaic proposes protections for bird islands
Mosaic also wants to reroute about 3,300 feet of North Archie Creek, which runs through the northern section of the proposed expansion area and empties into Tampa Bay. The creek was rerouted in 1984 as the existing gypstack was being developed, according to the Corps.
Mosaic is required by law to make up for potential environmental impacts, and the company has told the Corps it intends to purchase mitigation bank credits that can be used for habitat restoration elsewhere.
In addition to the required environmental mitigation, Mosaic is proposing to Hillsborough County protections for more than 300 acres of bayfront located between the Alafia River and Bullfrog Creek, according to a statement from company spokesperson Chloe Conboy Renard. The habitat includes mangroves, salterns and upland hardwood forest.
The properties making up Bird Island and Sunken Island — which were created in the 1920s as the Alafia River was dredged — are an important nesting site for birds but have no future land use or zoning designation, Renard said.
As part of the expansion, Mosaic is proposing to designate the islands for natural preservation to “provide continued protection of these critical natural resources,” Renard said.
In its review, the Corps has made an initial determination that Mosaic’s expansion “may affect but is not likely to adversely affect” threatened and endangered species, including green sea turtles, smalltooth sawfish, manatees, wood storks, Eastern indigo snakes and more.
The Army Corps’ public comment period opened Feb. 17 and will run until March 19.
Some environmental groups, including climate education nonprofit The CLEO Institute, have raised concerns about extending Mosaic’s wide-scale industrial facility closer to Tampa Bay’s coast in an area that’s vulnerable to storm surge and flooding.
