The Santee sinkhole in April.

The Santee sinkhole in April.

MARTHA ROSE BROWN, T&D

It wasn’t at the top of the S.C. Department of Transportation’s road-repair list but a fix has become essential for a sinkhole that threatens traffic at Old Number 6 Highway and U.S. 15/Bass Drive.

Sinkholes are not new for Santee, where the ground is filled with underlying deposits of limestone. Santee State Park, in fact, has a number of sinkholes.

By way of explanation, the website www.geocaching.com states the Santee area was covered with a shallow, subtropical sea approximately 40 to 50 million years ago.

“In this sea, millions of shelled microscopic and macroscopic animal thrived. When these animals died, their shells and skeletons, which were rich with calcium, settled to the ocean floor forming layers of sediment composed of clays, silt and minerals. Then for millions more years, additional layers of sediment and plant materials were accumulated. Pressure and chemical reactions transformed the sediment into limestone. Later, some of these limestone deposits eroded, resulting in the natural occurrence of sinkholes.”

The website notes that a sinkhole “typically begins to form when seeping groundwater (which is naturally mildly acidic) or an underground stream very slowly and steadily dissolves the calcium carbonate of limestone, which creates a crevice that expands as time passes. As the limestone continues to be dissolved by the action of the mildly acidic groundwater, these channels eventually expand to form submerged caves and large cavities are formed in the rock.”

The sinkhole near Old Number Six and 15 has become the most famous in Santee.

Its high profile began in 2009 when overnight a hole about 20 feet wide and 6 feet deep developed. It was not the first time the hole had appeared next to the Bank of Clarendon, but it was lot wider than five years before.

Then again in 2012, the sinkhole at the site made news, only this time the depth was 10 feet.

Earlier this year, the sinkhole expanded further and swallowed up a piece of the sidewalk on Old Number Six a few feet west of U.S. 15.

At the time, Mayor Donnie Hilliard noted the sinkhole continues to attract attention.

“We’ve had quite a bit of publicity on the sinkhole,” Hilliard said. “The sinkhole has been around for quite some time.”

But officials have decided it’s time to do away with the “attraction.”

Santee Town Council approved a resolution authorizing a Municipal State Highway Project agreement for sinkhole repairs.

“It’s gotten to the point where it’s starting to get into the shoulder of the roadway,” said Adam Humphries, program manager with the South Carolina Department of Transportation. “It is a risk to lose a major U.S. route.”

So just how will SCDOT battle Mother Nature for a permanent fix where temporary fills have not been enough?

SCDOT will come in, clean up the sinkhole, put riprap on the bottom, fill it with "flowable" fill and put in dirt and grass over the top of it, Humphries said.

“We feel this will reinforce it enough so it will be a long-term solution,” he said. “We let the project in June. It’s been recommended for award at the beginning of this month. The completion time is mid-September when we think it will be permanently done.”

Officials of the Bank of Clarendon Branch adjacent to the sinkhole will also have to find a permanent solution to the part of the sinkhole affecting its parking lot. Options include working with SCDOT’s contractor when it has equipment and personnel already on site, or selecting a different contractor on its own.

The sinkhole (in a way) will be missed, but with growing concerns about safety, taking action now is a priority for road and highway improvements in South Carolina.

As for the future, chances are good it won’t be Santee’s last sinkhole.

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