Clean air. Clean water. Now, clean caves?

Kentucky town leads a movement to protect the subterranean landscapes beneath much of the US.

Years ago, the picture would have been unthinkable.

Eyeless cave fish lurking in the dark pools of Hidden River Cave. Blind crayfish hiding in cool recesses of the limestone formations. Schoolchildren on educational tours, listening to the rush of the subterranean river.

That's because, for decades, the caverns beneath this rural Kentucky hamlet were little more than a natural septic tank. Homes and industries dumped so much waste into Hidden River Cave that the river ran green and yellow with toxins. The stench was so strong it filled Main Street on hot days.

Now, after a multimillion-dollar cleanup, Hidden River Cave is a vanguard for one of the least-known frontiers of pollution control: protecting similar subsurface landscapes, which underlie one-fifth of the US.

Indeed, these areas of limestone, dolomite, or other soft rock are the foundation for much of the upper South and the Eastern Seaboard. But here in south-central Kentucky, the health of these fragile formations are of particular importance, because this region is home to some of the most remarkable and extensive cave systems in the world.

What's emerging is a desire to apply the same vigilance used in fighting for clean air and water to the formations beneath our feet.

"You have a landscape that until recently was one of the more poorly understood landscapes in the world, and yet it is one of the most sensitive," says David Foster, executive director of the American Cave Conservation Association, which runs a museum in Horse Cave. "We're trying to get people to protect what they cannot see."

Crevices, caverns, and sinkholes form as water erodes soft rock. This terrain - called karst - is especially susceptible to pollution because it lacks the natural filtration provided by sand or soil layers. Surface runoff sinks directly into the ground, letting unfiltered toxins contaminate groundwater.

The result: About 10 percent of the cave systems in America have been seriously damaged by water contamination, in some cases threatening endangered species of fish, bats, and other creatures.

"Many of the hazardous waste sites in the eastern United States are on karst areas," says Tom Aley, director of the Ozark Underground Laboratory in Missouri.

Hidden River Cave is a textbook study in what can go wrong - and right - in conservation. The earliest residents here in the town of Horse Cave took refuge from hot weather on the cool, fern-lined banks of the cave, which yawns right beside Main Street. Hidden River provided electricity and drinking water, and tourists lined up to see the magnificent limestone domes and passageways.

Hidden River Cave has long been admired for its scenic beauty. Legendary naturalist John Muir even came here on his walk from Louisville, Ky., to the Gulf of Mexico.

"It seems like a noble gateway to the birthplace of springs and fountains and the dark treasuries of the mineral kingdom," he wrote in an 1867 account of his trek.

But within 100 years of Muir's visit, the cave almost had been destroyed.

Human sewage was piped directly into the caverns, and industrial waste from nearby farms and factories ran into sinkholes that drained into the cave river. The town switched to the Green River, 20 miles away, for its drinking water. In 1943, the cave was closed to tourists and remained off-limits for 50 years.

Later, in the 1960s, a primitive sewage plant pumped partially treated effluent into a sinkhole draining into the cave, compounding the problem.

"It got to be an unbearable smell," said longtime city clerk Ann Matera, who remembers downtown businesses stuffing charcoal behind their curtains to help neutralize the stench. "Some days, especially in the summer, you would invent things to leave work early."

Under pressure from the Environmental Protection Agency, Horse Cave officials joined with neighboring cities and Mammoth Cave National Park to build a $15-million-plus regional sewage treatment plant in 1989. Meanwhile, city leaders, led by Bill Austin, whose family owned the cave until last year, spearheaded an effort to reclaim Hidden River Cave.

Mr. Austin helped persuade the American Cave Conservation Association to move its headquarters to Horse Cave in 1986. The association then developed the nation's first museum dedicated exclusively to educating the public about the ecosystem underground.

With the new sewage plant built and fewer people using sinkholes as dumping sites, the cave recovered quickly. Now about 17,000 people a year visit this underground world.

"In a nutshell, we're talking about a natural resource that contains some of the largest springs and some of the largest groundwater supplies on earth, that provides natural habitat for rare species, that preserves archaeological history," Mr. Foster said. "There are a lot of reasons to care about protecting it."

(c) Copyright 2000. The Christian Science Publishing Society