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One sinkhole begets 200 after well-drilling

Published Sep. 12, 2005

It began as a routine well-drilling job.

Three weeks ago, an employee with Andy Kuka Well Drilling & Septic in Spring Hill was drilling an irrigation well for a future golf course at the new Heritage Pines development when something unexpected happened:

A massive sinkhole opened up and threatened to swallow the entire drilling rig. The operator and rig made it out in time, but a crane had to be used to retrieve a truck from a 150-foot-wide, 15-foot-deep sinkhole.

That wasn't the only problem. Within 24 hours, workers identified about 200 smaller sinkholes surrounding the large hole, at the southwest section of the 650-acre property, south of County Line Road one mile east of U.S. 19.

Most of the sinkholes were only a few feet wide, and all of them were triggered by the accident, a sinkhole expert said.

Construction at that part of the development has stalled since the accident.

And Wednesday, officials with the Southwest Florida Water Management District met with Heritage Pines developer U.S. Home Corp. to discuss the incident.

"We don't have a sinkhole problem," said Bob Fertig, president of the North Florida Division of U.S. Home. "We did have a well-drilling accident. Unfortunately, it's something that happens. It's not an unusual thing."

Nevertheless, the sinkholes are the talk of the neighboring Arlington Woods subdivision, where a small sinkhole appeared on a resident's property earlier this week. The sinkhole is about a quarter of a mile from where the accident occurred.

However, Swiftmud sinkhole expert Tony Gilboy said it's unlikely that the sinkhole off Green Park Road in Arlington Woods was related to the sinkholes at Heritage Pines.

And, he said, there is no indication that the Heritage Pines property is any more vulnerable to sinkholes than other areas of Pasco and Hernando counties, Gilboy said.

"This was just a freak accident," he said. "I guess you could call them induced sinkholes."

As a precaution, U.S. Home engineers will do additional soil borings and ground penetrating radar tests in the area where the accident occurred to ensure that there aren't other sinkholes in the vicinity, Gilboy said.

U.S. Home previously had done such tests for the property as a whole, not the area where the accidents had occurred, Gilboy said. The tests should be complete in the next week, he said.

"U.S. Home is a very cautious, conservative company," Fertig said. "Before we bought this property, we did a very careful geological analysis. We have absolutely total and complete confidence that there is no problem on this property and that this land is the safest anywhere."

Most of the holes will be filled in, except for the larger one, which will form a lake.

The accident will not delay construction of Heritage Pines, Fertig said. The 1,518-home retiree development is still in the early stages. The company has opened a few model homes and recently broke ground on its 18-hole golf course.

According to Gilboy, here's what happened:

The contractor had drilled a deep hole into the Floridan Aquifer for an irrigation well.

As he was pumping air into the hole to clean it out, a large underground cavern beneath the drilling rig collapsed.

The surge of several tons of dirt falling into the cavity caused a massive pressure wave through the aquifer, producing the 200 smaller sinkholes around the big hole.

Most of the holes were within the six acres surrounding the accident site, but some were spread over a 25-acre area, Gilboy said.

"It's very unique to have that many sinkholes in one place," Gilboy said. "The water well contractor was just in a very unusual spot."

Gilboy said heavy rains were likely a factor in causing the cavern to collapse. Sinkholes, produced by limestone cavities, are often triggered by heavy rains, which put pressure on the cavities and cause them to collapse. Sinkholes can also be triggered by too little water, as a result of overpumping, for example.

Heavy rains also probably caused the sinkhole that appeared earlier this week in Arlington Woods. The 4-foot-wide hole is between two homes on Green Park Road.

The owner of the home could not be reached for comment, but some Arlington Woods residents wondered whether the hole was related to any of the construction activity at Heritage Pines.

That's unlikely, because it appeared nearly three weeks after the other holes at Heritage Pines, Gilboy said. Though they agreed on what caused the sinkholes at Heritage Pines, Fertig and Gilboy contradicted each other on several points.

Fertig initially said there were only about 100 holes and that they were confined to within a few hundred feet. He later said those were rough estimates, though he disputed Gilboy's statement that the sinkholes covered 25 acres.

Fertig also said the holes occurred in a golf course area where no homes were planned. Gilboy said there were homes planned along that section of the golf course.

Fertig said such accidents are "very common" in his business.

Gilboy said otherwise.

"We had a very similar collapse just north of Weeki Wachee in 1979 when a contractor was putting in a monitor well," he said. "It happens. It's rare."