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Plan to plug landfill's sinkhole: $5.4 million, 15 months

Workers for the geotechnical firm Hayward Baker watch over a drill rig as grout is pumped into a sinkhole at the Southeast County Landfill to stabilize the hole and allow for further study. Complete repairs aren’t expected until June 2012.

Courtesy of Hillsborough County Public Utilities Department

Workers for the geotechnical firm Hayward Baker watch over a drill rig as grout is pumped into a sinkhole at the Southeast County Landfill to stabilize the hole and allow for further study. Complete repairs aren’t expected until June 2012.

BALM — As Hillsborough County officials this week unveiled a $5.4 million, 15-month plan to plug a massive sinkhole at the Southeast County Landfill, some residents who viewed the presentation took the opportunity to say, "I told you so."

"Why was the landfill built here in the first place?" asked Daniel Dixon, 60, a lifelong resident of Balm who attended an open house Tuesday at the University of Florida Gulf Coast Research Center. He said he and other local residents protested construction of the landfill off County Road 672 between Balm and Picnic in the early 1980s based largely on the proximity of then-existing sinkholes.

The landfill sinkhole, currently estimated at 50 feet deep and up to 129 feet wide, opened Dec. 14 in a garbage-filled area about 5,000 feet north of CR 672, officials said. Last week, workers began funneling grout into the sinkhole to stabilize it and allow further study. Complete repairs aren't expected until June 2012.

"This happened in December. This is March," Dixon said. "This is bad. Why hasn't it been taken care of?"

County officials and hired experts said the location of the sinkhole in a landfill filled with municipal waste and ash from incinerated garbage means a quick fix could put undue pressure on the damaged clay liner and lead to further environmental harm.

Among the biggest concerns: compromising the thick clay liner that prevents rain-soaked contaminants from seeping into the underground aquifer. The landfill is situated in a rural area where surrounding landowners tap that aquifer for drinking water and crop irrigation.

"We've got one shot at it," said Richard Siemering, senior project manager for HDR Engineering, the firm approved Wednesday by county commissioners to come up with a remediation plan.

"We want to do it right."

He acknowledged that a sinkhole in a landfill is bad news but said there's a silver lining: It opened on the side of a slope that makes rainwater penetration less likely.

"If we were going to design a sinkhole [in a landfill], that's where we would put it," Siemering said.

Monitoring wells have detected no contamination in groundwater near the sinkhole, but Dixon said the county's test wells are much deeper than those of surrounding residents who depend on the aquifer for drinking water. He said he lives about 2 miles from the landfill and said his family has depended on bottled water since the sinkhole occurred.

County officials promised free well-water testing to residents who requested it.

Irene Barnes, whose well is one of the closest to the landfill, said testing and sampling she paid for from a private company revealed no contaminants in her family's water supply, but she remains watchful.

HDR Engineering has a standing contract with the county for engineering services at the landfill. County Commission action Wednesday increased the amount HDR will be paid this year by about $1 million, from $882,000 to nearly $1.9 million.

The bulk of the $5.4 million allocated for sinkhole repair will go to construction once a fix is designed. The money will come from a Solid Waste Department reserve fund and is not expected to increase trash disposal rates, most of which are tacked onto property tax bills each year, said county spokeswoman Michelle Van Dyke.

Separately, HDR is being sued by water supplier Tampa Bay Water for alleged design flaws that led to cracks in the embankment of the C.W. Bill Young Regional Reservoir just north of the landfill. Repairs there have been estimated at $125 million, a cost the water supplier has said likely will increase rates for public water customers in the Tampa Bay area.

Hillsborough County is among member governments that buy water from the regional utility.

Siemering said he couldn't comment on the lawsuit but noted that HDR has a long history of landfill liner design. He said the firm also has hired some of Florida's best-known sinkhole experts at Tampa-based SDII Global Corp.

"We put together a professional team of geotechnical and sinkhole experts," Siemering said.

Van Dyke said the county is satisfied with HDR as the engineering contractor at the landfill and added, "We are fully confident in their ability to undertake this work."

Susan Green can be reached at

Plan to plug landfill's sinkhole: $5.4 million, 15 months 03/17/11 [Last modified: Thursday, March 17, 2011 4:30am]
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