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Tests find no water contamination from landfill sinkhole

The sinkhole that opened up last month at the county’s Southeast Landfill grew to about 60 feet deep by 110 feet wide. Possible groundwater pollution is a concern.

STEPHEN J. CODDINGTON | Times

The sinkhole that opened up last month at the county’s Southeast Landfill grew to about 60 feet deep by 110 feet wide. Possible groundwater pollution is a concern.

LITHIA — Nearly a month after a massive sinkhole yawned at the Southeast County Landfill, county officials say initial testing has shown no groundwater contamination.

In a community where surrounding households depend on well water, that's a big relief for people like Irene Barnes, whose well off County Road 672 is about a half mile from the site.

"I was a little bit concerned," she said, noting that she received the results of county testing on her well last week. She said county representatives also have shared plans for tackling the problem with her family.

"They've made efforts to ease our minds."

She and other neighbors said they have contracted with private companies to have their water tested and await those results.

Sinkholes can funnel above-ground toxins into the underground aquifer tapped by wells, making the phenomenon particularly troubling in the case of a landfill.

But sampled wells at the landfill and four privately owned shafts near the site have turned up no pollution, said Michelle Van Dyke, a spokeswoman for Hillsborough County's Public Utilities Department.

Officials first discovered a smaller opener Dec. 14, but it grew into a gaping hole, which in mid-December measured 60 feet deep and 110 feet across including surface cracks. Since December, soil subsidence has reduced the depth to about 50 feet, Van Dyke said Monday.

The county plans to inject a concrete grout mixture to stabilize the cavern while experts determine how best to fill it, Van Dyke said. Experts at HDR, a Tampa engineering company, are under contract with the county and are studying the complex opening.

Plans submitted to the Florida Department of Environmental Protection show officials hope to stabilize the hole by February, excavate the garbage and reclaim the area by June, when the rainy season typically starts.

Repairing the damaged landfill liner may take longer, Van Dyke said.

"It's very important to remember that this is not a pothole by the side of the road, nor is it a sinkhole in a typical location," Van Dyke said.

"We have to move forward very deliberately, very carefully, using the best techniques out there to minimize any further impacts to the environment."

Experts have said groundwater in the vicinity moves south at a slow rate, typically about a foot every 10 days. The county will sample existing wells at the landfill weekly until state regulators are satisfied that pollution no longer is a threat, Van Dyke said. Two new monitoring wells will be drilled near the sinkhole, she added.

Three of the private wells tested soon after the sinkhole opened, including the Barnes well, are sampled every three months according to the landfill permit. Another on Hal Colding Road was added at the owners' request, Van Dyke said. Two wells at the Hillsborough County Sheriff's Office target practice range off County Road 39 also were tested and showed no contamination.

The nearest private well that is down-gradient of the sinkhole site is about 1.5 miles away and has not been tested because of the distance, Van Dyke said.

The sinkhole also poses no threat to the C.W. Bill Young Regional Reservoir, which is north of the landfill, she said.

Joseph Reeves lives on CR 672 about two miles from the sinkhole.

The county has not offered to test his well, he said, but he's not worried.

"I'll get my well tested when I can afford it," he said. Meanwhile, he's impressed with the county's efforts to address the problem.

"I'm pretty confident they'll get it done," Reeves said.

The landfill is surrounded by farm land, including orange groves and strawberries, causing some neighbors to question whether groundwater pumping to protect crops during recent cold snaps could have caused the sinkhole.

Van Dyke said the cause may never be known. She said the area was studied and deemed to have low sinkhole potential before construction of the landfill began in the early 1980s. The facility opened in 1984.

Susan Green can be reached at hillsnews@sptimes.com.

Tests find no water contamination from landfill sinkhole 01/13/11 [Last modified: Thursday, January 13, 2011 3:30am]

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