Two years after it swallowed 215M gallons of polluted water, Mosaic sinkhole finally corked

Nearly two years after a massive sinkhole opened at Mosaic's Mulberry phosphate processing plant, a company spokeswoman says it has been sealed at last and will be completely filled by the end of May.

The state Department of Environmental Protection has approved demobilizing the deep drilling and grouting equipment used to fill the chasm "since the sinkhole now is sealed in accordance with the consent order requirements," said Mosaic spokeswoman Jackie Barron, which a DEP official confirmed.

All that's left is some cosmetic work, Barron said.

"We're currently working to fill the upper portion of the cavity, close the opening and level the surface," she said, predicting that would be done in the next two weeks.

This was no ordinary sinkhole. It was viewed at first as a potential threat to the area's water supply, and the way it was revealed prompted Gov. Rick Scott to push for a change in state law.

ORIGINAL STORY: Mosaic plant sinkhole dumps 215 million gallons of reprocessed water into Floridan Aquifer (w/video).

For Mosaic, which just announced that it's moving its corporate headquarters from Minnesota to Florida, filling the chasm took $84 million and 20,000 cubic yards of grout, a thick mixture of water, cement, and sand which hardens over time.

It also took nearly a year beyond what the company first expected. Mosaic officials first said workers would be done filling the hole in June 2017, then discovered a hole they had thought was 45 feet wide was closer to 100 feet wide, requiring far more grout.

But the company hopes this expensive project closes the book on a major public relations nightmare.

Workers at the plant first noticed something amiss on Aug. 27, 2016, when they checked the water level in a 78-acre pond sitting atop a 190-foot-tall phosphogypsum stack at the plant. They discovered the water level had dropped by more than a foot.

NOTHING TO SEE HERE: As polluted water disappeared in sinkhole, Mosaic avoided saying the 's-word'.

Slowly all the water atop the stack — 215 million gallons of it — drained away. Once the water was gone, on Sept. 5, Mosaic officials could see the sinkhole, which meant the water had fallen some 220 feet into the aquifer. Phosphoric acid process water, a byproduct of turning phosphate into fertilizer, is considered a pollutant.

Although Mosaic officials notified the DEP right away about the loss of water, they did not use the word "sinkhole" in communicating with the DEP until Sept. 9. Neither the company nor the DEP notified the public until Sept. 15, a full 19 days after the crisis started, despite the threat to the nearby drinking water supply.

At the time, state law did not require notifying the public unless the pollution was detected beyond the polluter's property. After a television report exposed the sinkhole and the spill, Mosaic issued an apology for not notifying its neighbors or the city of Mulberry.

NOTICE REQUIRED: After 3-week delay telling public about contaminated sinkhole, Gov. Rick Scott wants faster notice.

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Scott held a news conference condemning the delay in notification — even though his own DEP had kept silent too.

"It does not make sense that the public is not immediately notified when pollution incidents occur," Scott told reporters gathered near the Mosaic plant.

At his urging, the Legislature passed a new law on pollution notification. The law, approved by unanimous votes in both chambers, requires the owners of sites where such spills occur to notify the DEP within 24 hours. The agency then has a 24-hour deadline to publish those notices online where the public can see them.

Who is Mosaic: A primer on the new Fortune 500 company moving to Hillsborough.

Mosaic installed monitoring wells to track where the pollution went and put in pumps to draw it back out again. According to Barron, none of the acidic water has ever surfaced in anyone's drinking water.

Three residents living near the plant who draw their water from wells filed a federal lawsuit against the company in September 2016. But they dropped it last June without obtaining a settlement from Mosaic.

Sinkholes are far from rare in the area. In fact, Florida's limestone geology, known as karst, is so susceptible to crumbling that the state leads the nation in sinkholes.

One of the most notorious Florida sinkholes opened in 1994 at that same Mulberry phosphate plant where the Aug. 28 sinkhole opened. At 160 feet wide and plunging 200 feet deep, that sinkhole also sucked the pond from a gyp stack into the aquifer, like water draining out of a bathtub.

The 1994 sinkhole opened 1¼-miles away from the 2016 sinkhole. In that earlier incident, the public was notified within a week.

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