Drainage big concern in I-69 construction because of karst features along route

Karst, by definition, is an irregular limestone region with sinkholes, underground streams and caverns. Water forms those features by eroding the rock over thousands of years. In southern Monroe County, the limestone is very close to the surface, so it doesn't take much excavating to reach one of those features.

Many of the karst features along Section 4, the 27-mile stretch from Naval Support Activity Crane to Bloomington, were identified through experimental boring before construction began, Jobe said. However, as with any sub-surface features, some were discovered during construction, he said. When that happens, work stops. The transportation department's environmental team and structural engineers, along with officials from environmental regulatory agencies, all work together to determine the appropriate treatment, Jobe said.

Some of the features are small sinkholes about half the size of a vehicle, Jobe said. Others are much larger and classified as caves.

"That word may shock people," he said. "But they're probably not the size you're picturing."