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

The company said water quality problems will be “modest.”

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.