Dennis Black, the gypstack manager at The Mosaic Company's phosphate processing plant in Bartow, guns a large vehicle up the side of the dusty mountain.
"We're averaging just over 500 feet right now. We're permitted to go to 520," he says, over the roar of the SUV.
The stack is almost as tall as a 50-story building.
The view from atop the gypsum stack is regal.
The Lakeland skyline pokes out to the north. Bok Tower in Lake Wales can be seen to the east. On a clear day the towers of downtown Tampa scrape the western horizon.
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But the view looking this way isn't so scenic.
This is like the surface of the moon.
White dust coats everything. On the rim high above, backhoes claw through the toxic byproducts of fertilizer production, which are slightly radioactive. Not enough to hurt you, unless you breathe in nothing but phosphate dust for several decades.
The smell — well, it smells like plant food.
Water roars down in sheets from a pipe that gradually removes highly acidic water from inside the stack.
"See the lime pond to the right?" Black asks, pointing out his front window. "It goes into this lime pond, and that's how we capture the process water, and we get it back to the north side to feed the plant. So all the water's captured."
To the east, lime used to decrease the acidity of those evaporation ponds gives it a bright, unnatural green color.
These mountains are made byproducts from the production of fertilizer. They contain heavy metals dug up by huge machines that scoop and scrape the earth for phosphate rock. Inside the stack are hundreds of millions of gallons of "process water," liquid that contains diluted phosphoric and sulfuric acids and ammonia.
That's the work being done by Mosaic, the only fertilizer producer left standing in Bone Valley, where Polk, Hillsborough, Manatee and Hardee counties meet. It's the largest phosphate producer in the world. The Tampa-based company reported nearly $9 billion in revenue last year.
That's not the case at Piney Point, where a bankrupt company operating the gypstack there this spring failed to prevent a tear in the liner, sending hundreds of millions of gallons into Tampa Bay. Black says that's not likely going to happen here.
"We're up here seven days a week, doing maintenance activities," said Black, who has worked at Mosaic for 25 years. "And also we have technicians running around. They'll be doing visual inspections and documenting their inspections multiple times throughout the day."
Still, all the inspections in the world can't account for Mother Nature. Mosaic's own history demonstrates that.
In 2016, one of the deepest sinkholes ever recorded in Florida opened beneath Mosaic's New Wales Plant in nearby Mulberry, in southwest Polk County. More than 200 million gallons of polluted water spiraled into the underground aquifer. It took the company two years to seal the opening.
READ MORE: WUSF's Coverage Of The Piney Point Disaster
Company officials said they tested wells in the area to track where it went.
Two decades earlier in 1994, a sinkhole opened up at the very same site.
Mosaic also operates a fertilizer plant in Riverview, with two giant gypstacks perched on the edge of Tampa Bay. There, in 2004, high winds from Tropical Storm Frances bashed a hole in the dike around the pond, sending 65 million gallons of polluted water into Hillsborough Bay. Untold numbers of fish were killed, along with acres of mangroves and seagrass.
Mosaic spokeswoman Jackie Barron says they're doing everything they can to minimize any threats — including tapping into some innovative technology.
"We use drones. We do sonar. We have a monitoring well network that are constantly monitoring water level, in addition to water quality," she said.
Barron says they're also testing something called a geophone.
"It's micro-seismic," Barron said. "So they can detect the subtlest shift in movement."
Today, there's little possibility of eliminating these toxic mountains run by Mosaic or anyone else. One idea Mosaic supports involves road construction. Last fall, the Environmental Protection Agency approved the use of the byproduct called phosphogypsum for road base. But that idea is the subject of a lawsuit from a coalition of environmental groups, who want to keep it concentrated here in the gypstacks, instead of having it spread around.
Until a use gets the government's OK, the only option left is "closing" the gypstacks.
That's happened at five of Mosaic's gypstacks, including one in Plant City that recently got permission to close from state environmental regulators. They still have four gypstacks actively being used.
And it's starting to happen here at the Bartow stack, as it nears its limit of about 50 stories.
The 'closing' process could take years and depends a lot on how much it rains. It starts with plant operators treating the acidic water before it can be discharged off the property. The treated water will flow into natural wetlands before heading to the Alafia River, and then to Tampa Bay.
At Piney Point in Manatee County, the threat of a breach means operators need a quicker solution. They're opting to inject remaining process water below the underground aquifer.
Barron says Mosaic takes their responsibility seriously.
"The water that we discharge into nearby water bodies meets high water quality standards," she said, standing at an area south of the gypstack, where treated water flows into a natural wetland.
Once the acidic water is removed, Mosaic says it will cover the gypstack with an impermeable liner and then grass.
So what's going to happen to the fertilizer byproducts when this Mosaic stack in Bartow is closed? The mining continues, says manager Dennis Black. The waste will be moved to a gypstack that has been reactivated at Mosaic's nearby Green Bay facility, in southwest Polk County.
But not everyone is thrilled with that prospect. Jaclyn Lopez is with the Center For Biological Diversity, an environmental advocacy group. She says phosphate companies like Mosaic should stop adding to the problem.
"I'm open to exploring other things, but the first thing is stop making more of it," Lopez said. "Control what we have."
One thing that can be controlled is how much money is set aside to deal with any potential disasters at these gypstacks. Barron says Mosaic has a trust fund for that is around $600 million and growing. In addition, they have $245 million set aside for a Plant City gypstack that was purchased by the company from CF Industries — plus a $50 million line of credit.
That's just in case something happens to the company, insurance money will be used to close the stack.
