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Mosaic, state should have seen sinkhole forming, experts say

A massive sinkhole that opened underneath a gypsum stack at a Mosaic phosphate fertilizer plant in Mulberry dumped at least 215 million gallons of contaminated water into the Floridan aquifer.
A massive sinkhole that opened underneath a gypsum stack at a Mosaic phosphate fertilizer plant in Mulberry dumped at least 215 million gallons of contaminated water into the Floridan aquifer.
Published Feb. 15, 2017

UPDATE: Hydrologists who accused Mosaic and DEP of missing sinkhole signs say they were wrong

A year before a sinkhole drained 215 million gallons of contaminated water from the top of a Mulberry phosphogypsum stack, monitoring wells around the stack showed something was already going horribly wrong — something that two experts say indicated a sinkhole was forming.

Yet the stack's owner, Mosaic, did nothing. Neither did the state Department of Environmental Protection.

According to a couple who are retired hydrology experts, the data from those wells show that the level of the aquifer jumped 40 feet. That would not happen naturally, they said.

Instead, it was a sign that solid material from the gyp stack had dropped into the aquifer, boosting the water level like an ice cube dropped into a glass of iced tea.

The only explanation for that happening, they said, would have been a sinkhole just starting to form, just like the ones that occurred there before.

"They should have seen this 2016 sinkhole coming," Don Rice, a hydrologist who retired from the U.S. Geological Survey in 2011 and now lives in Parrish, said Thursday. "Alarm bells should have been going off — danger, danger!"

Neither Rice nor his wife, Mary Hrenda, a retired New Jersey Department of Environmental Protection hydrogeologist, believe any of the contaminated water on top of the stack drained into the aquifer at that point. That, they said, is all the more reason to blame Mosaic and the state Department of Environmental Protection for failing to take action a year earlier.

"When they saw those levels rising, they should have shut down that gyp stack until they could see what was happening," Rice said.

If Mosaic had pumped the contaminated water from on top of the stack then, the company could have prevented it from dropping into the aquifer last year, he said.

Rice and Hrenda are scheduled to take part in a news conference that phosphate mining opponents are holding at 11 a.m. today at the Manatee County Courthouse, where they will talk about their findings.

Neither Mosaic nor DEP officials wanted to comment Thursday on the accusations of negligence until they could look at the data that Rice and Hrenda used. However, a DEP spokeswoman said the agency does regularly check the monitoring well reports that the couple studied.

"We do review all the monitoring data that's submitted as required to ensure compliance with Florida's environmental regulations," DEP spokeswoman Lauren Engel said.

Mosaic spokeswoman Eileen Stuart tried to discourage the Tampa Bay Times from reporting on the retired hydrologists' accusation, calling it "wildly speculative."

Because of what Rice and Hrenda found, Andy Mele of the environmental group Suncoast Waterkeeper, who chairs the Coalition to Stop Phosphate Mining, is sending a letter to Gov. Rick Scott, Attorney General Pam Bondi and the U.S. Environmental Protection Agency demanding they investigate whether DEP and Mosaic were negligent.

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"I'm calling it a smoking gun," he said.

Mele and other phosphate mining opponents are holding their news conference today because the County Commission is slated to vote Wednesday on whether to allow Mosaic to expand its mining there. If the expansion is approved, some of the mined phosphate would be brought to the Mulberry plant near the Polk-Hillsborough county line for processing.

Mosaic's Mulberry plant is the largest fertilizer factory in the United States. Yet it's also built in the middle of an area riddled with sinkholes, according to data from the Florida Geological Survey.

One of those sinkholes, which opened in 1994 and measured 160 feet wide and 200 feet deep, occurred 1¼ miles from the one that opened last summer. It swallowed all the contaminated water that was pooled on top and dumped it into the aquifer.

Afterward, the state required Mosaic to put in monitoring wells around the 704-acre gyp stack to check for problems. The reports are posted on the DEP's website and are available to the public, Rice said.

Since then the company has twice had other problems within the stack. In 2004 and 2013, Mosaic discovered what it called "sub-surface erosion features" that required repairing before they became sinkholes.

Then, last Aug. 27, Mosaic employees noticed the water level had dropped in the 78-acre pond of polluted water atop the stack. However, they and the DEP waited until Sept. 6, when all 215 million gallons of water had drained out, to identify the problem as a sinkhole — one that was 45 feet wide and 220 feet deep.

Even then, no one informed the plant's neighbors, whose drinking water comes from the same aquifer, or the general public. Not 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. DEP Secretary Jon Steverson said he did not inform Gov. Rick Scott until after the story hit the news.

So far, according to the DEP and Mosaic, none of the contaminated water has shown up in the more than 1,000 private wells they have been sampled around the plant site, and Mosaic has begun pouring grout into the sinkhole to seal it up. DEP officials say their investigation of the sinkhole incident is continuing.

Contact Craig Pittman at craig@tampabay.com. Follow @craigtimes.


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