http://www.theledger.com/news/20161017/mosaic-to-start-sealing-new-wales-sinkhole-by-december

The Mosaic Co. will start sealing off a sinkhole that dumped 215 million gallons of contaminated water into the Floridan Aquifer by December, a company executive said Monday

By Kevin Bouffard

@polkbizbeat

MULBERRY — The Mosaic Co. will start sealing off a sinkhole that dumped 215 million gallons of contaminated water into the Floridan Aquifer by December, a company executive said Monday.

And the company will continue pumping water out of the aquifer for the next several years until tests show no traces of contamination, said Herschel Morris, vice president of operations.

Morris spoke Monday at a news conference at Mosaic’s New Wales fertilizer plant — site of the September accident.

"Mosaic is absolutely committed to getting this thing right," he said.

Morris discussed details of a high-tech mapping of the sinkhole's underground area and said the first step is sealing off the sinkhole.

The company also announced it had test results from 588 residential water wells among 763 tested near the plant as of Monday. None shows contamination from the accident, a statement said.

Tests did show 10 wells did not meet one or more federal drinking water standards, but Morris said the problems are not related to the accident.

"That water, however, is similar in quality to samples analyzed by the U.S. Geological Survey and the Southwest Florida Water Management District in eastern Hillsborough (County) and western Polk County that had not been impacted in any way by industry," Mosaic said in a statement. "The results continue to indicate that they are in no way associated with the New Wales sinkhole incident."

A map provided by Mosaic showed it had tested as far as 20 miles away from the sinkhole into the Lakeland area and northeast Manatee County. As of Friday, the company had received 1,050 requests for the third-party residential well testing and had filled 692 requests to provide bottled water.

The accident involves water sitting atop a gypsum stack near the New Wales plant. Gypsum is a byproduct of phosphate fertilizer manufacturing and can be stored only in piles, or stacks, that can reach hundreds of feet above the ground.

A Mosaic technician monitoring the New Wales stack noticed a 2-foot drop in the pond level Aug. 27, which was attributed to a sinkhole, according to a company account. On Sept. 5, that sinkhole opened to its current size of about 45 feet across and drained the pond into the aquifer below.

Environmental issues with the pond water include contaminants such as salt, sulfates and radium, which is slightly radioactive.

Mosaic and the Florida Department of Environmental Protection, which was notified of the accident immediately, faced heavy public criticism for not notifying the public of the sinkhole and threat to the aquifer until almost three weeks later. Mosaic officials apologized for the delay.

In mapping the sinkhole, Mosaic used a technology called “LiDAR” for “Light Detection and Ranging” that uses pulses of laser light reflecting into mirrors to measure dimensions in remote places, Morris said.

The LiDAR units are more commonly attached to aircraft or drones, he said, but in this case Mosaic attached them to steel cables similar to ones used by overhead cameras at NFL games. That enabled the unit to be lowered into the sinkhole and maneuvered around.

“It takes a very sophisticated computer to interpret all those pulses, but it’s a very simple procedure,” Morris said.

The results show the sinkhole extends about 220 feet below the top of the gypsum stack and 25 to 30 feet below ground level, he said. The cavity extends from about 40 to 150 feet in diameter below the surface.

Blocks of gypsum from the stack lie at the bottom of the sinkhole, which Morris compared to a pile of bricks. The cracks between blocks form channels that allow water to seep through to the aquifer.

“It’s about what we expected,” Morris said of the LiDAR map. “Probably the only surprise is we thought there would be water at the bottom. There is no water.”

The plan calls for pouring a concrete substance, or grout, onto the bottom of the sinkhole to seal off any further water penetration, he said. The company will then fill the rest of the hole, probably with gypsum.

The process should be completed by late May or early June, Morris said.

But Mosaic will continue to pump water from beneath the sinkhole area for use at the fertilizer plant for several years after sealing the sinkhole, Morris said. Pumping will continue until the company is confident it has recaptured all the contaminated water that seeped into the aquifer.

The contaminated water contains “signature molecules” found only in the gypstack pond water, he said. Once tests show water pumped up from the area contain none of the signature molecules, the company will know the cleanup has been completed.

The Mosaic plan resembles the same technology used to seal smaller sinkholes that erupt commonly in Florida, said Brian Birky, executive director of the Florida Industrial and Phosphate Research Institute in Bartow, an academic agency affiliated with Florida Polytechnic University.

“It’s the same kind of technology but on a grander scale,” he said. “They’re doing the right thing by gathering as much information as they can about the geology and shape of the hole.”

Using gypsum as a filler material after sealing the bottom of the sinkhole does not present an environmental concern because it would harden into a solid mass, Birky said.

“It’s got impurities that are already there in the rock, so they’re not adding anything that wasn’t already there,” he added.

Marian Ryan, a spokeswoman who follows the phosphate industry for the Sierra Club of Florida, said she didn't know enough about the sinkhole plan at this time to comment.

— Kevin Bouffard can be reached at kevin.bouffard@theledger.com or at 863-401-6980.