Polluted water from Mosaic phosphate plant likely spilled to Tampa Bay during Milton

Hurricane Milton’s relentless rainfall caused a water collection system to breach at the Tampa-based phosphate company Mosaic’s facility in Riverview, likely spilling an unknown amount of polluted water into Tampa Bay, according to a statement from the Fortune 500 company.

The Riverview facility stores a stack of phosphate waste called phosphogypsum, a byproduct that contains radium, which decays to form radon gas. The Riverview “gypstack,” which towers over Tampa Bay’s eastern shores, saw nearly 15 inches of rain during the storm, according to the company statement.

Milton’s deluge overwhelmed the facility’s system designed to collect water, and stormwater began dumping out of a manhole at the Riverview plant, according to Mosaic. Officials at the company believe that stormwater then entered into a drainage outfall that empties into Tampa Bay. The company said it expects water quality issues to be “modest.”

The company hasn’t provided an exact volume of polluted water that leaked, but said it may have been greater than the 17,500-gallon minimum amount required to report a spill to regulators. When reached by phone Monday morning, the company’s senior environmental advisor for the Riverview plant, Dara Ford, also did not provide an exact volume spilled. According to a pollution notice the company filed to state environmental regulators, the incident lasted for 12 hours, beginning at 2 a.m. Thursday and ending at 2 p.m.

“Back-to-back historic storms crossed our operational areas,” the company said, adding that facilities withstood the storm with “few challenges.”

Florida environmental regulators were on site at the Riverview facility on Friday collecting water quality samples, according to Florida Department of Environmental Protection spokesperson Alexandra Kuchta. Additional information about the severity of the event, including the results of those water tests, were still unknown as of Monday morning.

Justin Tramble, executive director of Tampa Bay Waterkeeper, said “it’s no surprise” to hear about the incident.

“Every storm, every significant rainfall event we are crossing our fingers that there are no big spills. Something has to change, because that hope isn’t good enough. We need better federal and state oversight or we’ll constantly be avoiding disasters,” Tramble said. His organization sued over the 2021 Piney Point wastewater disaster where a federal judge recently found the facility’s former owner, HRK Holdings, liable for the ecological disaster.

“We’ve known for years that these sites are public health and environmental land mines,” Tramble said. “There are no regulations that adequately protect the public from hazards associated with phosphogypsum.”

Tramble said Tampa Bay Waterkeeper will be monitoring the spill.

Hours before landfall, the Tampa Bay Times ran an analysis underscoring the risk Hurricane Milton posed to Bone Valley, the swath of land through central Florida that’s home to most of the state’s phosphate mining and production facilities. The Times found that 22 of Florida’s 25 phosphate waste sites, including Mosaic’s gypstack in Riverview, were in the major hurricane’s direct path.

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Company spokesperson Luiz Mauricio Pereira said Mosaic last week idled all Florida operations ahead of Hurricane Milton to mitigate potential impacts. Power has been restored to all facilities, and ports in the region have re-opened, he said. The facilities are expected to return to full production capacity over the coming days as cleanup finishes.

Hurricane Milton caused widespread environmental issues — whether its sewage pollution from wastewater facilities or chemicals running off into rivers — and it’ll be hard to tease out the specific water quality impacts coming directly from Mosaic’s Riverview plant, according to Maya Burke, an assistant director of the Tampa Bay Estuary Program. With so much rainfall and runoff pollution, it will take a while for both Tampa Bay and the Gulf of Mexico to rebound to a healthy level.

“I don’t think we have a utility in our area that hasn’t had significant sanitary sewer overflows of some shape or form. We’re looking at hundreds of millions of gallons of things that are containing bacteria and nutrients,” Burke said. “The bay and the gulf are going to be hurting, and it’s going to be a death by one thousand cuts.”

Times staff writer Shreya Vuttaluru contributed to this report.