The Florida Department of Environmental Protection (FDEP) reported that “multiple acoustic detections” were indicated by a seismic monitoring system at The Mosaic Co.’s New Wales South Phosphogypsum Stack from Oct. 8-18. The system was required as part of the permit requirements for the facility to provide early detection of any potential geologic changes in subsurface conditions at the site.
According to an Oct. 21 letter from FDEP to Mosaic, FDEP concluded that the information provided “indicates the presence of a subsurface condition that has the potential to adversely affect the integrity of the phosphogypsum stack.” FDEP advised Mosaic that authorization to commence phosphogypsum stacking operations in the Phase II East area cannot be provided without knowledge of whether there are any new subsurface features that may require further exploration to determine whether stabilization is needed.
FDEP outlined that Mosaic is to provide daily reports of its investigation and emphasized that follow-up exploratory drilling, along with any additional steps needed to further investigate this subsurface condition, must be completed as expeditiously as possible.
FDEP told Green Markets that it and the State Geologist are reviewing the non-routine report notification and information provided by Mosaic, and that at this time there is no indication that a sinkhole has occurred or that there are any concerns with the structural integrity of the phosphogypsum stack system at the site.
However, it said the seismic results have indicated subsurface activity was detected that warrants further investigation to determine whether Mosaic is required to implement preventative or remedial actions to protect the integrity of the phosphogypsum stack to ensure protection of water resources.
Mosaic had not responded to inquiries at press time.
FDEP noted that after completing the remedial repairs related to the 2016 sinkhole at the New Wales facility (GM Sept. 16, 2016; May 25, 2018) under the Consent Order issued on Oct. 24, 2016, Mosaic was required to evaluate and implement technologies to investigate the subsurface beneath the South Phosphogypsum Stack at New Wales.
That review led to the identification of a technology that Mosaic is now using for ongoing monitoring of any potential subsurface activity beneath the South Phosphogypsum stack. The monitoring and reporting are intended to be one part of an early detection system for subsurface activity at the site.
Further, this monitoring system allows Mosaic to identify any potential unknowns and take proactive measures to maintain safe operations before a significant subsurface incident can develop and impact the facility.
Total costs to repair Mosaic’s 2016 sinkhole have been reported as over $80 million (GM Aug. 3, 2018). The sinkhole was sealed in 2018.
Earlier this year, FDEP allowed an emergency release of wastewater from Mosaic’s Piney Point phosphogypsum stack into Piney Point Creek, which leads into Tampa Bay, after there were fears that the leaking stack would collapse (GM April 2, 2021). Local residents were evacuated as a precaution.