Report: Drainage project caused Georgetown sinkhole

GEORGETOWN, SC (WCSC) - Georgetown's drainage project caused the huge sinkhole that damaged several businesses last year, according to a new report.

Several businesses are still empty and unsafe because of the damage done by the sinkholes.

Now, owners in the area are taking matters into their own hands by filing a lawsuit against the contractors and the Department of Transportation.

According to the Georgetown Times, the sinkholes that formed between July and November of 2011 were caused by runoff water.

Neighbors continue to feel those effects more than a year later. Most people in the area say they're just ready to put this headache behind them.

In the report released by the SCDOT provided to WMBF News by the Georgetown Times, information gathered by F&ME Consultants 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.

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