SCDOT seeks cause for Georgetown sinkholes

GEORGETOWN, SC (WMBF) - The South Carolina Department of Transportation released a "cause and effect" report in an attempt to explain why sinkholes suddenly developed in downtown Georgetown.

There were a total of seven sinkholes that formed between Highmarket and Prince Streets in the second half of 2011, causing the sudden collapse of many businesses and homes.

"It's really affected people. The car dealership, it's gone. The UPS store, that's gone. The insurance company, it's gone, too," expresses Mary Kinlew, a neighbor in the area.

In the report released by the SCDOT provided to WMBF News by the Georgetown Times, it shows the primary reason for the sinkholes forming were because king piles were being installed by the run off tank next to City Hall.

King piles are a type of support system.

"If they didn't do that drainage thing, this may not have happened," suggests Kinlew.

During the construction of the drainage project, the report shows water was removed too quickly, causing the ground to crumble.

Neighbors in the area believe this concept should have been common sense to contractors.

"Obviously if you're taking it out, it's got to go somewhere," says Justin Harper

According to the report, construction going on near the ground level did not play a part in causing the damage. It also shows existing utilities didn't hurt, either.

The SCDOT stresses that this report is not to place blame on any particular person or company. They say it is to show the cause and effect of the sinkholes that are still leaving a void in the downtown area.

Over a year later, neighbors are still feeling those affects.

"There were some businesses, and there are still some now that are being affected by it," explains Gerald Williams, a resident of Georgetown.

And his neighbors agree.

"They're not doing anything to bring more business in here, for the people to work. They really need jobs," says James Elder.

Harry Oxner, a local attorney, is representing 6 business owners in the area. Just last week, they filed the first lawsuit against the DOT and the companies responsible for the drainage project.

Here is a portion of the information gathered by F&ME Consultants which led them to determine the following:

Based upon the information provided to and gathered by F&ME, the sinkhole/depression formation which has occurred in the vicinity of Front, Hazard, Highmarket, and Dozier Streets in Georgetown, SC beginning with the first documented sinkhole on Hazard Street and including at least six (6) other subsequent sinkholes/depressions was caused by construction activities related to the City of Georgetown Storm Drainage Improvement Project which impacted the lower, confined aquifer system which underlies the area in question.

The specific construction activities include: 1) Primary Cause: the installation of king piles for the wet well located on the block with City Hall; and 2) Accelerating Factor: construction de-watering activities which rapidly removed water from the lower, confined aquifer.

The 30 inch outside diameter (O.D.) king pile installation required the installation of 36 inch O.D. temporary casing and the drilling of 30 inch holes through the aquifer confining layer (aquitard) and into the limestone lower confined aquifer.

The identified de-watering activities which resulted in pumping of large quantities of water which flowed from the lower confined aquifer through the holes drilled in the confining layer (aquitard) for the king piles were: 1) during the excavation for the wall penetration in wet well for the installation of the 52 inch wall sleeve/48 inch steel force main outfall pipe; and 2) during the excavation of the wet well area for the construction of the concrete bottom slab.

The noted pumping activities for the de-watering of work areas associated with the wet well construction resulted in a substantial volume of water flowing from the lower confined aquifer. This flow reduced the upward hydraulic pressure within solution cavities in the lower confined aquifer. The reduced upward pressure resulted in an increase in stress in the aquitard and localized collapses of the aquitard into the solution cavities. The collapse or breach of the aquitard allowed the sandy soil deposits above the aquitard to flow down and into the exposed cavities resulting in the observed sinkholes and depressions. (See Sketches 2, 3, and 4)

We have found no evidence that existing utilities contributed to the formation of the identified surface sinkholes and/or depressions. We have found no evidence that the shallow construction activities (above the noted aquitard) have contributed to the identified surface sinkholes and/or depressions.

After the sinkholes formed, Highway 17 through the town was closed temporarily to clean up the debris. The drainage project resumed in 2012.

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