Two retired hydrologists who last week accused Mosaic and state regulators of ignoring signs of a sinkhole at a phosphogypsum plant a year before it drained polluted water into the aquifer now say they were wrong.
"We made a mistake, and we sincerely regret our error," Donald Rice and his wife, Mary Hrenda, of Parrish said in an email to the Tampa Bay Times on Tuesday.
Rice is retired from the U.S. Geological Survey and Hrenda worked for the New Jersey Department of Environmental Protection. Last week, the pair joined with the environmental group Suncoast Waterkeeper in calling for an investigation of Mosaic and the Florida Department of Environmental Protection.
The sinkhole in question was detected in August at the company's New Wales plant near Mulberry. It measured 152 feet wide and 220 feet deep. Officials said the hole allowed 215 million gallons of contaminated water to drain from atop a gypsum stack into the aquifer below.
After analyzing the DEP's online records regarding Mosaic's Mulberry fertilizer plant, Rice and Hrenda spotted what they believed to be a telltale sign that the sinkhole discovered in August actually started opening up in 2015.
The water level in the aquifer jumped 40 feet, and they concluded the only possible explanation was solid material falling into it from inside the phosphogypsum stack.
Mosaic and the DEP said the hydrologists' findings were "fundamentally wrong."
Both said the reports the two hydrologists had examined were from a well used to monitor a 1994 sinkhole near a closed gypsum stack, not the active stack where the August sinkhole was discovered. The wells are used to monitor the closed site for underground activity, and the reports are posted on the agency's website and are available to the public.
The DEP also said the change in the aquifer was caused by Mosaic injecting grout into the closed gypsum stack. However, Mosaic has declined to answer questions about why grout is being pumped into that closed gypsum stack. A DEP spokeswoman said the company was doing it to deal with "subsurface erosion" within the stack.
Mosaic and DEP officials also complained that the Times should not have reported on the hydrologists' allegations, which the pair made public at a Suncoast Waterkeeper news conference held Friday on the steps of the Manatee County Administrative Complex in Bradenton.
Price said neither he nor his wife have had any direct contact with Mosaic. But after a Times reporter sent them statements from the company and the state agency criticizing their findings, the couple said they took another look at the state records and agreed with the explanation from Mosaic and the DEP about what caused the aquifer to rise by 40 feet.
Company and state officials said Tuesday that they would not comment further beyond the statements they sent out last week.
"The allegations . . . are fundamentally wrong," Mosaic said in a statement Friday. "The water level increases . . . were observed in a location that is in no way related to the recent sinkhole."
The state said it was aware of the work that led to the aquifer jump because it "was carefully reviewed by DEP staff to ensure compliance with Florida's environmental regulations."
Officials said the first sign of the Mulberry sinkhole was detected on Aug. 27, when Mosaic employees noticed the water level had dropped in the 78-acre pond of polluted water atop the stack. The company and state agency officially declared the problem a sinkhole on Sept. 6, after the 215 million gallons of water had already drained out.
However, no one informed the plant's neighbors, whose drinking water comes from the same aquifer, or the general public about the sinkhole. It wasn't until a WFLA-Ch. 8 reporter called to check on rumors of a sinkhole on Sept. 15 — three weeks after the pond began draining — did the public learn about what happened.
The company apologized for its secrecy, and Gov. Rick Scott has vowed to change state law to require companies and governments to publicize such incidents within 24 hours.
So far, according to the DEP and Mosaic, none of the contaminated water has shown up in the more than 1,000 private wells that have been sampled around the plant site.
Mosaic has also begun pouring grout into the August sinkhole to seal it up. DEP officials said their investigation of the sinkhole incident is continuing.
Contact Craig Pittman at email@example.com. Follow @craigtimes.