Fast-growing area may face sinkhole risk
Karst, to those in Delaware County, can be either a fascinating science or a foreboding menace. And many, including those whose homes lie above it, may be unaware of it.
Geologists use the word, derived from the German name for a region of northern
Italy known for its limestone plateau, to describe a topography formed when soluble rocks such as limestone and dolomite degrade underground. The areas are prone to voids, caves and caverns. They may swallow ground water. Sometimes, they lead to settling of terrain or even sinkholes.
A spine of karst runs along western Delaware County, through Concord, Scioto and Radnor townships, one of the denser concentrations in central Ohio.
Especially for those seeking to develop land in Concord, there is a “potential subsurface threat,” according to the Ohio Geological Survey, which maps the terrain.
Sinkhole concentrations of up to one per acre are common and can range from 10 feet wide to more than 100 feet.
The land is “among the most rapidly developing areas of the state, which means karst should be a consideration in site assessments for commercial and residential construction projects,” according to the state agency.
Joe Garrett, a Concord Township trustee and lifelong resident, said he was unfamiliar with the term
But he’s grown up around caves and sinkholes, mostly on private property and some with very steep drop-offs.
“We do have a lot of those caves. Growing up here, we were told don’t go anywhere near them,” said Garrett, 49. “Farmers used to throw their junk in there: a dead cow, all kinds of stuff.”
As for potential dangers from settling, “If there’s a potential for problems, we would love to know about it. I’ll probably look into this a little more,” Garrett said.
Delaware County officials are not overly worried, however, since karst evolves over thousands, or even millions, of years, said Scott Stephens, district administrator of the Delaware County Soil and Water Conservation District.
Plus, said Stephens, “Our limestone is much more durable” than in other parts of the country.
“My thought would be, ‘When does that clock run out?’ “said Garrett. “That may be 5,000 years, but are we on year 4,999?”
Land developers must carefully evaluate before investing time and money, said Rob Riley, Delaware County’s chief deputy engineer.
“It’s really something you work around, altering drainage and street layout design,” Riley said. “It’s something we need to be aware of.”
Home builders are drawn to the county for its interesting geological features, including bluffs, rivers and ravines.
Karst, said Charlie Driscoll, president of Edwards Land Co., is “kind of a scary term for everyone, because it’s kind of a sinkhole.”
Developers surveying a potential build site will often walk the land, he said.
Karst formations are fairly obvious, he said, “because you’ll have a ravine that heads toward a spot and then it disappears. And you say, ‘Huh? Where does this water go? Usually there’s a sinkhole right there at that point.”
Builders often will lodge boulders near the surface, “so kids don’t fall into them,” said Driscoll, who sees more reason to worry about other subterranean dangers.
“When you have a peat bog on your property or an underground spring, and your sump pump runs constantly, that’s a bigger problem,” Driscoll said.