By Linda Greene
South-central and southwestern Indiana has buildings, roads and bridges built on apparently solid ground. Yet below the surface is a complex system of limestone caves, sinkholes, bedrock springs, conduits (caves human can’t fit into) and swallow holes (that take in water). This collection of surface and underground features is known as “karst.” It has a kind of Swiss-cheese physiography.
Indiana’s Monroe, Lawrence, Greene, Orange, Crawford, Harrison, Jennings, Jefferson, Owen and Putnam counties all contain karst. It’s a distinctive characteristic of this area and worthy of our interest and care.
Karst areas have springs that issue from caves and conduits and are environmentally sensitive because of their effects on drinking water. Constructing buildings, roads and bridges over karst requires special procedures. Collapse of the surface into underground voids may jeopardize buildings and other structures.
Karst contains open conduits for contaminants to enter. Those contaminants – for example, from run-off from agricultural pesticides, herbicides and feedlots – taint the groundwater, which provides drinking water to people with wells.
When groundwater is contaminated, surface water is contaminated, also. Preventing the contaminated water from entering swallow holes and sinkholes can require the use of peat filters, which have a limited lifespan. The filters have to be replaced periodically, causing added expense.
In land with solid rock beneath, karst water filters through the soil and into sinkholes down to where the water enters the fractures or other voids in the bedrock.
Numerous sinkholes and springs are present in the I-69 highway corridor.
The public tends to regard karst as a nuisance, even though it is so important ecologically. People use sinkholes to dispose of trash without regard to contaminating their neighbors’ wells or springs.
Building on karst, as the Indiana Department of Transportation (INDOT) is doing with the new-terrain I-69 highway, is tricky because karst isn’t solid rock. Sinkholes have to be plugged up before the highway is built over them. In the worst-case scenario, parts of the highway could collapse over sinkholes and other karst features.
INDOT, however, is ignoring the sensitive karst area that the highway is supposed to traverse. According to Sam Frushour, a retired head of the Field Services Section of the Indiana Geological Survey, who evaluated karst in that capacity for 20 years, it makes little sense to install a highway over karst. The cost of remediating the karst features is many times higher than the cost of building a road on solid ground, without so much karst, such as U.S. 41 and I-70. Many Indiana citizens have advocated this route since INDOT made the highway plans public, over 20 years ago. Changing the highway’s route would nearly eliminate karst problems and decrease costs.
It’s impossible to know where all the karst features lie, and it’s very expensive to identify and build a highway over them. If contractors find water on the highway to be draining into a sinkhole, they have to install drains, and there’s no guarantee they’ll work. Plugging a small sinkhole properly, to federal highway standards, costs up to a million dollars. A large one can cost several million dollars
Very large sinkholes, which are unavoidable with I-69’s new-terrain construction plans, are “enormously expensive” to remediate, according to Frushour.
Road construction crews are encountering many karst problems, costing more than what INDOT estimated, because until crews drill and dig, no one knows what’s under the ground. “When you move soil,” Frushour said, “you find things you didn’t know about.” Currently, earth drilling has been cheapened so problems that would have been forecast will be missed until actual road construction.
Sometimes highway designs have to be redone.
We know from landowners whose property INDOT contractors are testing that the contractors are finding voids as they prepare to construct the highway.
Governor Daniels told INDOT to “throw out the rulebook” when building I-69 – that is, to build it on the cheap. However, as an interstate, the highway has to meet federal standards. That isn’t being done. Either the Federal Highway Administration is looking the other way, or it’s lowered its standards. None of this bodes well for the highway’s costs or public safety or for the ancient terrain in south-central and southwestern Indiana.
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