Mosaic seeks Riverview gypsum-stack extension; neighbors warn of environmental risks

Mosaic asked the Hillsborough County zoning hearing master on April 27 to expand a phosphogypsum stack at its Riverview facility and add roughly 1,412 acres to an existing planned-development district, a request that drew both community support and sharp opposition.

Shelley Thornton, Mosaic’s director of land‑use permitting, told the hearing master the company needs a lateral extension of the East Stack to provide “approximately 16 years” of storage capacity. Thornton said the proposed East Stack extension would involve about 178.5 acres of new disturbance within the stack footprint and would affect degraded wetlands and streams. To compensate, Mosaic proposed a multilayered mitigation package that includes purchasing and placing a permanent conservation easement on about 347 acres of land south of the Alafia River, and engineered restoration…