Posted by: rainworks | December 17, 2010

On the 33 Yard Line, to the Aquifer Below

Hillsborough County landfill sinkhole continues to grow

By Ileana Morales, Times Staff Writer
Posted: Dec 16, 2010 03:55 PM


TAMPA — The sinkhole in a Lithia landfill continues to grow, now measuring 80 feet wide and 60 feet deep.

Cracks on the edge have broken down since Wednesday, when the hole was 75 feet wide and 45 feet deep at Hillsborough County’s Southeast County Landfill. Thursday’s growth comes from preliminary estimates, and the deepest point of the hole remains 100 feet away from an aquifer below, officials said.

“There’s a significant amount of buffer between how deep the hole is and the aquifer,” said Michelle Van Dyke, community relations coordinator, for the Hillsborough County public utilities department.

It’s too early to tell if the expanding sinkhole is a threat to the aquifer, Van Dyke said. There will be more information about the impact of the sinkhole once engineering experts can get into the hole, but she said it’s not clear when exactly that would happen.

“Everything has to be done very deliberately and very carefully,” Van Dyke said.

While the sinkhole came as a shock to those who manage the landfill, it’s occurrence is not that unusual.

“It’s not a surprise that one would occur almost anywhere,” said University of South Florida geography professor Robert Brinkmann, who has studied sinkholes for 20 years.

Brinkmann said sinkholes form when limestone mixes with water and dissolves, leaving behind and underground void. Any sort of destabilization over those voids – for example, by pumping large amounts of water onto farms – can lead to sinkholes.

“It tends to be a trigger,” he said.

But a sinkhole is not likely to be caused by ground water pumping unless it is close to where the water is being pumped, he said.

The Florida Department of Environmental Protection asked the county to take immediate steps for them to evaluate what the sinkhole could do to surface water and groundwater quality.

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