Lessons Learned from the Seffner Sinkhole Tragedy

In Residential Blog Posts by John Topa

The Seffner Sinkhole tragedy demonstrates how unpredictable cover collapse sinkholes can be. While sinkholes are part of living in Florida, we don’t expect them to form inside our homes and when they do, they can cause catastrophic damage to property and, in rare instances, endanger lives. The incident in Seffner, however, was unusual in many ways:

The house had been tested for sinkholes.

In the days following the tragedy, the news media indicated that the house had been tested for sinkhole activity just a few months before. I noticed that there was angry public outcry. How could the experts have missed a sinkhole that was 30 feet wide and 20 feet deep?! The answer to this question is in the condition of the house before it was demolished.

If you were following the story closely, you know that there were many photos and video footage of the house. From the outset, it was apparent that the exterior of the house showed no signs of damage whatsoever. Ralph Meder, geologist at MCD of Central Florida, suspects that this is the reason the house was not tested further. The inspector, hired by the insurance company, likely performed a walkthrough inspection, looking for the common signs of sinkhole activity both inside and outside of the house. Not finding any, the inspector reported back to the insurance company who then granted the homeowners a sinkhole loss policy.

Nothing indicated that the homeowners suspected that there was a sinkhole problem. They simply wanted coverage in the event something happened. Sinkhole testing is expensive and insurance companies will not pay for it unless there are visible signs of possible sinkhole activity. If the insurance company had determined there was sinkhole-related damage to the house — the homeowners would never have been granted sinkhole loss coverage.

Further testing may not have detected the sinkhole.

For additional insight, I talked to Ralph Meder. Ralph said that even if the house had been thoroughly tested for sinkholes using today’s most advanced tools such as Electrical Resesitivity (ER), Ground Penetrating Radar and Standard Penetrating Radar (SPT), the sinkhole that took Jeff Bush’s life would most likely not have been found. “The only way they would have detected this sinkhole,” said Ralph, “was if they had taken the equipment into the house, drilled through the concrete, and bore a hole into the limestone.”

Had the outside of the home been tested for “significantly likely to imminently collapse” in the soils supporting the structure — through the use of shallow borings (down to 30 feet) — the sinkhole may still not have been found. Even if engineers had detected the presence of the sinkhole, they may have not noticed anything that predicted “imminent collapse.” The potential for imminent collapse — meaning a sinkhole is about to open up causing catastrophic damage — is what geologists and geotechnical engineers look for when deeming a property unsafe for people to live in.

The house was small;
how could there be a 30-foot wide sinkhole under it?

One of the biggest points of confusion came with the news of how wide the sinkhole was. I read several angry comments that mentioned the impossibility of a sinkhole of that width being under the house. “The house itself isn’t 30-feet wide,” wrote one person. “That bedroom couldn’t be much bigger than 10 x 12 feet,” wrote another. When aerial photos of the sinkhole began to appear on TV and in newspapers, the outcry became louder.

“One thing, people don’t understand is that all we can we see aboveground, is the “hole” left by the cover-collapse sinkhole,” said Ralph Meder. The true size of the cavity exists under the ground in the limestone. For example, some of Florida’s underground caverns are actually old sinkholes – cave divers have to squeeze through a small opening at the ground surface to gain access to the immense, watery limestone caverns beneath the ground.

In Retrospect

It is not productive to worry endlessly about what happened in Seffner. In Florida’s long history, sinkholes have rarely resulted in death. That said, however, the Seffner sinkhole serves as a warning about the consequences of human activity. Ralph Meder theorized that the Seffner sinkhole may have been associated with low water tables. As the population grows, the need for water increases. The overpumping of groundwater diminishes the water pressure that keeps the limestone bridges that top underground caverns from collapsing under the weight of the soils above them. Limestone bridges can collapse suddenly and unpredictably.

The bottom line is this… If your house is showing signs of serious structural damage, as in sinking or sagging – get out! Then, contact your property insurance adjuster right away. Just remember, however, you are more likely to be hit by lightning than falling into a sinkhole.

If you suspect you have a sinkhole, call the experts at Helicon Foundation Repair. As a recognized leader in sinkhole remediation and with over a decade of experience, Helicon Foundation Repair has completed thousands of successful projects.

At Helicon, we keep our promises. For more information, please call us today at 813-567-1065.