Sinkholes continue to plague city and county
Crews worked through the night on July 13 to repair a large sinkhole near the Darlington intersection of Pearl and caused by the collapse of a clay sewer pipe.
Photo by Samantha Lyles
By Samantha Lyles, Staff Writer, slyles@newsandpress.net
It’s become a common sight around the City of Darlington and Darlington County – the orange cones surrounding ruptured asphalt and piles of rust-colored clay indicating another sinkhole has appeared, rendering some road either treacherous or impassable. Though work crews from the city and county (and sometimes from SCDOT) respond quickly and toil until the damage is patched, some days they can barely stay ahead of the problem. In July and August, more than 115 sinkholes opened up around Darlington County, indicating that this problem won’t be going away anytime soon.
Darlington city manager Howard Garland says that many of the sinkholes the city deals with are caused when old clay sewer pipes collapse, causing the double trouble of sinkhole repair and water/sewer service interruption.
“When a sinkhole appears, the first thing we do is check city maps to determine exactly where it is and who is responsible for repairing it. Depending on the location, it could be the city, it could be the county or DOT,” Garland says.
If the sinkhole is caused by a clay pipe failure, the city deploys repair crews and replaces the clay pipes with durable plastic conduits. In severe cases like the July 13 collapse at the intersection of Pearl and Syracuse Streets, crews must dig up and replace the failed pipes from manhole to manhole – a costly project that eats up thousands of dollars in man hours and city resources.
While state and local governments have established routines for sinkhole repairs, little can be done to predict where they might occur. Around 20-percent of the U.S. is vulnerable to sinkholes because those areas rest over karst terrain where the subsurface rock is soluble, like limestone. These carbonate materials dissolve when groundwater circulates through them, causing susceptibility to sinkhole development. Darlington County is situated on a knot of karst terrain located beneath the Pee Dee, so when the weather pairs long dry stretches with sudden heavy rains, the earth can literally give way beneath our feet, our cars, even our houses.
The USGS (United States Geological Survey) says that when rainfall filters down through the soil, carbonate rock begins to dissolve and spaces and caverns develop underground.
“Sinkholes are dramatic because the land usually stays intact for a period of time until the underground spaces just get too big. If there is not enough support for the land above the spaces, then a sudden collapse of the land surface can occur,” reads the USGS description on their website.
USGS says sinkholes can be characterized into two types: cover-collapse sinkholes, which can develop suddenly and cause major damage to property and structures, and cover-subsidence sinkholes, which form slowly as the ground gradually deflates. Sinkholes vary in size and severity, ranging from a few feet wide to hundreds of acres, and from a few feet deep to over 100 feet deep.
It is unlikely that such a deep sinkhole would develop locally because the limestone layer underneath Darlington County is relatively thin. A thicker layer of carbonate soil – like that beneath Florida – leaves open the possibility of sinkholes deep enough to swallow houses whole. Such an event occurred in February of 2013, when a massive sinkhole opened beneath a home in Seffner, Florida and the home (and its sleeping occupant) vanished into the abyss. USGS says the most damage from sinkholes tends to occur in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania.
Not all sinkholes are natural; they can also be man-made, forming when construction alters natural water-drainage patterns, or when industrial and runoff-storage ponds are created. Adding heavy weight (whether that’s a road, a building, or a drainage pond) can trigger supporting material underground to collapse and form a sinkhole. Also, when aquifer systems are tapped for water supplies, the change in groundwater fluid pressure could cause a sinkhole.
With heavy rains forecast for the coming months, homeowners and motorists should stay alert for the appearance of sinkholes on their property and on public roads. If you see an unmarked sinkhole in or near a public road, please call 911 immediately and report the location so emergency responders can take appropriate action.
