POLK COUNTY, Fla. (WTSP) -- About six months after a massive sinkhole opened up at Mosaic's fertilizer plant near Mulberry, crews are still working to fill it.

The company let 10News WTSP take an up-close look at the sinkhole Thursday morning.

When it first opened in August, it sent 215 million gallons of radioactive water into Florida's aquifer. In addition to filling the sinkhole, they’re working to pump that water up. Mosaic built a water treatment plant on site to purify it.

“I can tell you, I believe we're going to seal this hole,” Herschel Morris, vice president of operations at Mosaic’s New Wales plant, said.

The plan to seal it is complicated, but simply put, they're going to pump a concrete and gravel mixture into it.

“Originally the sinkhole was about 220 feet below the surface,” said Jeff Golwitzer, the project manager. “We've added approximately 45 feet of concrete to the base of that stack.”

That's about a thousand cement trucks worth of concrete, and they've still got a long way to go. They need so much they're making tons of it at the site of the sinkhole.

Meanwhile, Mosaic is studying its land, trying to figure out if another sinkhole could open up and how to prevent that.

“When sinkholes started here in Florida, years and years and years, gazillion years ago, we have a lot more information about that today,” Morris said.

The price tag on this entire project could be up to $70 million. It's something they don't want to have to do again.

Morris said if you live near the well, there's no reason to worry about your drinking water. He said the contaminated water that went into the aquifer has stayed on Mosaic’s property.