Looking down into the 45-foot-wide hole, water flowing over the side plunges like waterfalls into depths that reach all the way to a Florida aquifer. Surrounding the hole is cracked grey rock, reflective of the shifted earth.
The sinkhole opened near Mulberry, FL, leaking acidic water. Later, gypsum from a gypsum stack at a Mosaic Company phosphate fertilizer plant leaked 215 million gallons of contaminated water into a Central Florida water source, according to officials from the company.
The collapse that happened at Mosaic is not a rare occurrence in the state. Sinkholes are common in Florida and can happen in both rural and urban areas for a variety of reasons.
They’ve opened on I-4 and even on USF’s campus, although these incidents varied in size and hypothesized cause, according to Philip van Beynen, associate professor in the school of geosciences.
While Van Beynen has not gone to study the incident at Mosaic, he is aware of the geological processes that can result in sinkhole formations. Sinkholes can form, Beynen said, when the roof of an underground cave collapses due to the weight above it. In the Mosaic case, the cave was filled with water that was part of the aquifer.
“So, when all that weight is pushing down on it, the roof can’t survive anymore,” Beynen said. “That leads to the collapse, which creates the sinkhole.”
The danger of the Mosaic sinkhole includes the risk of contaminated water leaving the area and getting into the groundwater local residents use, according to Sarina Ergas, a professor and graduate program director in civil and environmental engineering.
Limestone, the rock that makes up much of Florida, is porous, meaning it allows water to flow through it, she said.
The aquifer is a “patchwork” of tight spaces and large caves, meaning groundwater flows at different speeds, according to Beynen.
“Now, Mosaic said that the closest well, the water would take something like … three years to get there, but that’s probably just saying ‘Well, here’s a solid lump of rock and this is how quickly water can move through that rock,’” Beynen said. “That’s not Florida limestone. It’s full of holes, like … Swiss cheese or a sponge. That’s kind of what it looks like.”
Mosaic is currently working on extracting the contaminated water, but Beynen is unsure whether they will be able to get all of it out. Beynen is unsure. The extraction involves using a well and sucking up the water, which will remove both the contaminated water and the aquifer water, Beynen said, but due to the amount of water in the aquifer and the fact that it is currently the wet season, the extraction won’t have a large impact.
Beynen said the water contamination won’t spread to the point where it would affect Central Florida cities like Orlando or other large residential areas. The full extent and effect of the sinkhole and contamination is something about which Beynen could not give a definitive answer.
“It’s always an educated guess because we don’t have all the data,” Beynen said.
Last fall, a much smaller sinkhole opened on Sycamore Drive, three feet long and three feet wide on the surface. However, the ditch was approximately 10 feet wide, seven feet long below the surface and about four to five feet deep.
However, Beynen said a small sinkhole like the one on Sycamore, which happened during the dry season, could be attributed to a lowering of the water table instead of a case of too much weight.
In urban areas, Beynen said, nontraditional sinkholes on roadways can be caused by leaky pipes. The one on I-4, he said, was due to the pumping out of groundwater to keep strawberry crops alive during the cold season. Sinkholes are more common toward the coast, according to Beynen.
The higher elevation of campus compared to its surrounding areas puts it at a lower risk for sinkholes due to more sediment of bedrock, serving as a protective layer, Beynen said. He mentioned that heavy buildings on campus can be a risk, however, or construction that takes way some of that protective layer.
“Generally, the thicker the sediment you have above a sinkhole, the less likelihood it is you’re going to get a sinkhole,” Beynen said.
Contamination due to a sinkhole opening up underneath a building, Beynen said, would often be less than that of a sinkhole that breaks sewer pipes or opens underneath a chemical plant. In cases like the sinkhole that opened on Sycamore, Ergas said the contamination would be less serious and involve less serious compounds than the one at Mosaic.
Mosaic has stated that it will test residents’ wells for contamination, as some inhabitants surrounding the sinkhole have expressed concern both with the water contamination and Mosaic as a company.
Ergas encouraged concerned residents to get the water tested but make sure the compounds and chemicals that are causing concern are being tested for, instead of tests for things like bacteria, which are unrelated to the contamination.
“I’d say it’s not a dire emergency, but if people do have concerns then they should take Mosaic up on their offer to test the water,” Ergas said. “If they are concerned about Mosaic’s results, then they should get the water tested independently, but to make sure they’re testing for the right things.”