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The hole under the mountain

Published Oct. 4, 2005

Twenty mountains of chalk-white rocks soar over Central Florida's pancake-flat landscape, a scene from the moon.

They are artificial, the result of years of stockpiling gypsum, a waste product from the manufacture of fertilizer.

And it was Monday, June 27, 1994, when workers discovered something inside one of them that was unprecedented in the history of Florida's phosphate industry.

Workers at the fertilizer manufacturing plant, owned by IMC-Agrico Co., were making a routine inspection of the plant's top section when they noticed what appeared to be a ledge.

They got close enough to realize it would not be wise to go any closer. A very big hole had opened.

It wasn't until supervisors flew overhead in a helicopter that they saw the full extent of the sinkhole and muttered words that can't be printed.

The hole in the gypsum stack was very big and very deep.

It would eventually be measured at 160 feet across at the top, tapering to a shaft 106 feet wide and nearly 400 feet deep _ almost as deep as the Barnett Bank building in St. Petersburg is tall.

Local wags in this area near Mulberry, at the Polk-Hillsborough county line, dubbed it "Journey to the Center of the Earth." Some suggested stuffing the hole with the entire Polk County Courthouse, which has been closed due to sick building syndrome.

Instead, what developed was an unusual engineering project to plug the hole and an ongoing debate about the safety and fate of all the gypsum stacks that dot Florida.

What immediately worried the staff of IMC-Agrico and state environmental regulators about the sinkhole at New Wales was the potential for contamination of groundwater.

Water could be seen flowing out the sides of the shaft and down to the bottom. Between 2 and 6 million gallons of wastewater stored at the top of the stack disappeared down the hole.

Those fears were confirmed two weeks later when elevated levels of contaminants began showing up in monitoring wells at the plant site.

Gypsum _ or, more fully, phosphogypsum _ is a waste product from the manufacturer of phosphoric acid, a key ingredient in several common forms of fertilizer.

The gypsum is piped in liquid form to the top of the waste pile, which gradually grows upward. Contaminants in the gypsum, such as heavy metals and radioactive radium, can seep out the bottom.

The company started the stack in 1975. It was considered full when it hit 200 feet high, and IMC-Agrico opened a new one in 1993.

The surface of the old stack, where the sinkhole occurred, is as hard as concrete. But rainwater soaks down through the pile, where the gypsum becomes soggier.

Generally, the downward flow is slowed by a layer of clay just below ground level.

But if the New Wales stack is a big toxic bonbon, then the sinkhole took a bite. Unknown to anyone, the sinkhole was slowly eating its way upward, creating a cavity in the confining layer beneath the stack.

Sinkholes form when water dissolves the limestone that underlies much of Florida. The weight of the stack above _ totaling 100 million tons _ could have helped triggered the collapse.

The resulting groundwater contamination, as measured by the plant's on-site monitoring wells, was not especially alarming to the company or state regulators.

Levels of all contaminants, including the nastier metals and radioactive materials, were within the state's safety limits for groundwater contamination. The one exception was sulfate, but it was serious only if the water was used for drinking. This water is not.

The state Department of Environmental Protection also tested some residential wells bordering the property and found no contaminants, said Sam Zamani, administrator of the agency's phosphogypsum management program.

Nevertheless, the DEP asked the company to correct the problem.

The contamination was especially worrisome because it had reached the Floridan Aquifer, a huge body of underground water that underlies most of west Florida and is the sole source for major wells.

IMC-Agrico has an on-site well that draws up to 8.6 million gallons of water a day from the Floridan for use in its fertilizer manufacturing. The company has consistently maintained that rate of pumpage is enough to suck up any contaminants coming from the stack. State regulators agree.

The company's willingness to do repairs was partly motivated by self-interest.

If the hole continued to produce elevated levels of contaminants, they could have damaged the plant's steam boilers and required expensive treatment.

But there were also public relations considerations. The DEP was getting calls from CNN, the Associated Press, even a newspaper in Israel _ all wanting to know what was being done about the monster hole.

"If there's a perception we're contaminating the Floridan Aquifer, we couldn't do it," said John Brafford, IMC's vice president for phosphate operations. "The Floridan is considered sacrosanct."

The company spent about five months consulting with engineering experts and state regulators to formulate a repair plan _ from scratch.

No sinkhole like this had ever been plugged before.

The eventual plan was to fill the underground cavity opened by the sinkhole with concrete. But finding the right tool was a challenge.

The company had to drill shafts about 400 feet at an angle from the top of the stack. Conventional drills wouldn't do.

Eventually, IMC-Agrico brought in a 150-ton drilling rig normally used in the construction of steel foundation supports for buildings.

Starting in November, workers drilled 50 holes into the underground cavity left by the sinkhole, which measured about 130 feet deep.

That allowed them to pump in concrete evenly and systematically to seal up the "throat" of the sinkhole, the opening to the deeper Floridan Aquifer.

Once that was completed in late February, water began filling the 220-foot shaft above ground level _ and the contaminant levels began to taper off.

IMC officials say they went well beyond a minimum fix-up. Workers continued to pump in concrete at high pressure _ as much as 800 pounds per square inch _ to fill in all the nooks and crannies inside the cavity, which was strewn with boulders from the cave-in.

When they finished in April, IMC had pumped in 3,791 cubic yards of concrete at a total cost of $6.8-million.

The job is not finished.

The company plans to fill the 220-foot shaft above the cavity _ a void measuring another 42,000 cubic yards _ by pumping liquified gypsum back to the top of the old stack.

The DEP approved that work last month, and IMC-Agrico says it should be done by year's end.

Overall, officials say they are satisfied with the repair job.

"They responded very aggressively to the problem," said Brian Sodt, a manager with the Central Florida Regional Planning Council. "I never felt IMC was withholding resources."

The level of contaminants has been decreasing at the rate predicted by the company's consultant, and Brafford says they should approach normal background levels by the end of this year.

However, not everyone is so pleased.

Environmentalists such as Gloria Rains of ManaSota '88 argue that the monitoring wells may not have picked up the full extent of contamination yet, and that some may have escaped off site, although they offer no specific evidence to support that.

Instead, the environmentalists point to more general studies that suggest a need for tighter regulation or elimination of all gypsum stacks in Florida.

Most of the 20 stacks, which together weigh a total of 600 million tons, have no plastic liner between the bottom of the stack and the earth beneath. IMC-Agrico became the first company to voluntarily design one with a plastic liner in 1993, at a total cost of $75-million. The state now requires plastic liners for all new stacks.

Twelve of the 20 stacks have been found to violate groundwater safety standards, although just one of those released contaminants off the plant's property line. And the contamination tends to be in aquifers close to the surface, not the deeper Floridan, Zamani said.

DEP is requiring monitoring of the 12 stacks, although for the most part the contaminants are sucked up by on-site wells, Zamani said.

John Ryan, director of the League of Environmental Organizations, has suggested the DEP order the immediate closure of all the unlined stacks to pressure the industry to open new, lined facilities. Sinkholes could develop elsewhere.

Like many environmental debates, however, the underlying science is hotly contested.

The DEP does not think that is necessary, Zamani said. So, the agency has given the phosphate companies until 2001 to prove the stacks are not harming the environment. If they can't, then they must close them.

Closing the stacks would mean topping them with plastic and soil to end water seepage.

"My guess would be this is a big hurdle in front of them," Zamani said. "It will be a tough test to demonstrate" the stacks are not hurting the environment.

Brafford of IMC-Agrico contends it's an unsettled legal question whether state law prohibits groundwater contamination that does not extend beyond a plant's property line.

The industry has attacked an Environmental Protection Agency report that criticized the gypsum stacks by saying it was a preliminary, incomplete draft. A separate EPA report found IMC-Agrico's stack at New Wales did not present a toxic threat.

Phosphate companies have also argued that central Florida has naturally occurring high levels of radioactive materials, and the gypsum stacks make that condition no worse.

As for the threat of more sinkholes, central Florida has a relative abundance of clay, which retards the flow of groundwater, says IMC-Agrico's consulting engineer, Nadim Fuleihan of Ardaman & Associates Inc. Brafford says the IMC sinkhole was probably a freak occurrence.

And don't expect gypsum stacks to go away, the industry says. Its slogan, "Phosphate Feeds You," is meant as a reminder of how its product is a key reason for higher food production worldwide and relatively food low prices.

Environmentalists blame the overuse of fertilizers for helping to choke lakes and rivers with weeds.

Rains of ManaSota '88 says the DEP could force the industry to convert to different manufacturing techniques that would not create huge gypsum waste piles, although it would cost more.

Diana Youmans, a spokeswoman for IMC-Agrico, said the company has examined that alternative and found it would not be economical and posed other environmental problems.

Rains says the industry's political connections have kept the DEP from being tougher on it.

"DEP is anything but candid on the impacts of phosphate mining," she said. "They basically take what the industry says as gospel."

For now, the stacks will continue to loom over Florida's landscape. Although the industry would like to sell the gypsum as roadbed material, the EPA has banned it for that use because of its elevated radioactivity.

"This stack is being managed as well as gypsum can be managed," said Youmans of IMC-Agrico. "Until we find a new use for it, we're doing the best we can."

A huge gypsum stack

The scale of the gypsum stack is epic, even gargantuan. IMC-Agrico's stack at New Wales covers 430 acres at its base and is 130 acres at its flat top. It would cover most of downtown Tampa, stretching north-south from Interstate 275 to the waterfront area in front of Harbour Island and east-west from the convention center to the cruise ship terminal.

How big was the hole?

The hole in gypsum stack measured 106 feet wide and was 220 feet deep. Add to that depth a 35-foot sand layer and another 130 feet of confining layer where the sinkhole was located and it totals 385 feet from the top of the stack to the bottom of the sinkhole. For comparison, St. Petersburg's Barnett Tower is 27 stories or 385 feet tall.

How a sinkhole forms

Water seepage from the top of the stack creates an underground cavity that grows upward through the confining layer. The weight of the stack above eventually causes the confining layer to collapse. At this point, the material in the gypsum stack begins to pour into the cavity, like sand into an hour glass.