It doesn't sound like anyone, including the EPA, is unduly concerned. But as with everything these days, the story will be sensationalized and politicized. It does contain that trigger word 'radioactive' after all
A more informative article on the situation is in the Tampa Bay Times. The fertilizer by-product has only low-levels of radioactivity and was a small part of the overall volume of waste water which is mainly just acidic water. The spill is contained and has not gone beyond the Mosaic property. The plant is operating as normal.
Mosaic plant sinkhole dumps 215 million gallons of reprocessed water into Floridan Aquifer (w/video) | Tampa Bay Times