By Dan Klepal
The Cincinnati Enquirer

The Tristate sits on shaky ground. Actually, it sits on dissolving ground, and that makes it shaky - and dangerous - in many places.

Click to view a PDF infographic showing a detailed look at how karsts can allow pollutants into drinking water. (PDF file 328k)

Limestone serves as the bedrock foundation on which most of Kentucky, Indiana and Ohio rest. Over eons, rainwater has dissolved that foundation in areas of thin topsoil, creating a web of cracks and crevices, called karsts, in the bedrock.

Karsts develop naturally all across the world. About 40 percent of U.S. land east of Oklahoma has karsts, while about 55 percent of the Bluegrass state and 100 percent of Florida sits atop cracking ground.

Karsts are responsible for great works of natural beauty when, over hundreds of thousands of years, those cracks and crevices grow into caves - such as the world's largest cave system, Mammoth Cave near Park City, Ky. Karsts have a powerfully destructive force when the ground above them rapidly collapses in the form of sinkholes.

But the most common danger karsts pose is to people - about 100,000 people in the Tristate - who use wells to tap a spring or aquifer for drinking water. Karsts allow rainwater to flush pollutants - such as pesticides, fertilizers or sewage - into the groundwater with no filtration.

Rich Bendula, a geologist with the Ohio Environmental Protection Agency, said sewage from leaky septic tanks is the most serious threat to people who live atop karsts and use wells for drinking water. The OEPA will launch an educational campaign, warning well water users about the dangers of karsts this spring.

"When you look at man-made contaminants, like solvents or uranium, you're looking at exposure and risk over a lifetime in the form of an increased chance of getting cancer," Bendula said. "But you can drink a glass of water contaminated with e.coli and become deathly ill, or have a lifetime problem with your kidneys."

That threat extends to rural restaurants and other businesses that use wells.

The problem is especially acute around the Tristate, with many older homes in rural areas, said Bob Moore, an environmental specialist with OEPA's Division of Drinking and Ground Waters.

"It's real important for them to become educated on what kind of well they have and how it was constructed," Moore said. "Some of those wells are nothing more than a hole in the rock and are really susceptible to contamination."

Dennis Hull, assistant state geologist with the Ohio Department of Natural Resources, said rainwater dissolves limestone because it is naturally acidic. More acid is added to the mixture as rain comes into contact with dying vegetation. Then, as karsts start to form, small particles of dirt and rock washed into the cracks help further erode the limestone as it dissolves, quickening karst formation.

"You can imagine with each rainfall, the solution of bedrock decreases a little bit," Hull said. "It's an ongoing process that takes thousands of years. Some of the actively forming karst features we see today have largely developed since the end of the ice age" 10,000 years ago.

But limestone bedrock is only half of the equation making the Tristate rich karst country. The other reason is that this area was the end of the line for glaciers during the last ice age. That means the massive movement of ice, dirt and rock left much less topsoil covering the limestone in this area than further north. And that, Hull said, makes it easier for rain to get to the underlying bedrock.

"As you move up the Lake Erie basin, the (topsoil) gets much thicker and protects the limestone," Hull said.

There's one clear rule of thumb for anyone using a well: Don't drink cloudy water after a rainstorm.

Rebecca Petty, administrator of the residential water and sewage program at the Ohio Department of Health, said cloudy drinking water after rain is a sure sign of contamination.

"If the water gets muddy, that means there has been a flush of bacteria into the groundwater," Petty said. "In those cases, people need to get their water tested."

Petty said it's important for people to know what kind of well they have, the depth and where their septic tank is in relation to their drinking well. Information about when, how and at what depth drinking wells were constructed is available through Ohio's Department of Natural Resources.

It's equally important for people on well water to make sure not to have pesticides or fertilizers around their well.

"The rule of thumb is keep everything at least 50 feet away from a drinking well," Petty said. "That includes buried propane or fuel oil tanks."

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E-mail dklepal@enquirer.com