Sinkhole Drains Stack Pond at Florida Fertilizer Plant

Overhead view of the sinkhole that remains after a leak drained 215 million gallons of water from a
plastic-lined stack pond at Mosaic’s New Wales, Florida, phosphate operation.
On September 15, fertilizer producer Mosaic Co. announced that a 45-ft-wide sinkhole had mostly drained a phosphogypsum stack pond into a regional aquifer system which underlies an area of about 100,000 mi2 (260,000 km2) in the southeastern United States. However, the plume was contained to the New Wales facility’s property, near the central Florida city of Mulberry, and the damage could be remediated, Mosaic said.

“On Saturday, August 27, water level monitoring showed a decline in the water levels for one of the two cells of our active stack, the west cell,” Mosaic said. The company did not specify if it was a vadose (erosion) or a collapse sinkhole that drained the west cell of the South Stack. Mosaic stated the sinkhole “formed under the cell” and “we believe (it) damaged the liner system at the base of the stack. … We believe the sinkhole reaches the Floridan aquifer.”

Upon detecting water level decline in the pond, Mosaic said it began “pumping water out of the west cell and into an alternative holding area on-site to reduce the amount of drainage. At this time, we have begun the process of recovering the water by pumping through on-site production wells.” Mosaic described one well as “24 in. in diameter and 800 ft deep.”

Mosaic has contracted Environmental Consulting & Technology Inc. (ECT), which is coordinating with the U.S. Environmental Protection Agency (EPA) to collect and test water from neighboring wells. “As of (October 4), Mosaic has received 850 well water test requests. ECT is prioritizing testing based on neighbor’s proximity to the New Wales facility,” Mosaic said. “The samples will be analyzed for minerals and other parameters that are indicative of the type of water that was released as a result of the sinkhole.”

It also encouraged well owners seeking an alternative means of testing to receive a water test at no cost from the Florida Department of Environmental Protection. On September 28, Mosaic stated, “results of radiological testing conducted at nine water wells located in close proximity to Mosaic’s New Wales facility have all returned results that are within normal drinking water standards.” Mosaic offered free bottled water to neighbors who request it.

The plume will likely be recovered, according to Mosaic. “Water within the Floridan Aquifer in the vicinity of the New Wales facility generally moves to the west, and at a slow pace—around 1,000 ft per month,” Mosaic said. “That pace allows us to recover water from the gyp stack in the aquifer by pumping it through our well. That well is located west of the gypsum stack and taps into the Floridan aquifer.”

Walt Precourt, Mosaic’s senior vice president–phosphates, said, “We are working with experts to develop a plan to plug the sinkhole, which will likely include the use of concrete-like grout to seal the pathway that opened into the aquifer.”

The New Wales facility was slated for closure in a consent decree filed with the United States District Court for the Middle District of Florida in October 2015.

As featured in Womp 2016 Vol 10 -