I step into an elevator and push the button; the car descends the equivalent of 23 stories in 30 seconds. When survey team members and I step out, we enter Jewel Cave, the third-longest cave in the world.

Since 2005, I’ve helped to survey unmapped areas of this subterranean labyrinth on the edge of South Dakota’s Black Hills. The experience has taught me a lot about what lies beneath the earth’s surface.

Solid as a rock — that’s how most of us think of our planet. But my underground exploration has shown me that the earth is anything but solid. It’s almost impossible, for instance, to predict what a cave passage will or will not connect to deep underground.

That’s one reason the British Columbia-based Powertech Corp. proposal for an in-situ uranium mine in southwestern South Dakota is a bad idea. Here’s the Reader’s Digest version of the mining process. In-situ is Latin for “in place,” so the uranium is “mined” where it is found, underground. Powertech plans to drill into the uranium-bearing rock, then pump in fluids that cause the uranium to bind with the liquid.

That liquid, composed mostly of water, moves through the pervious rock layer. Additional wells would be placed in the direction that the liquid is expected to travel, and the liquid, now carrying uranium, gets pumped out. The uranium is then extracted from the liquid and turned into yellowcake, which is later refined.

Exposure to radioactive uranium, of course, is not good for human health. Conventional mining leaves behind piles of radioactive waste rock. Open-pit mining stirs up radioactive dust, which can travel great distances in the wind.

Powertech project manager Mark Hollenbeck, a chemical engineer and a local rancher, claims in-situ mining is safer and more environmentally friendly than conventional mining. He calls it “arthroscopic.” One could argue that keeping the rock and dust underground is safer.

But there are potential problems underground. The water that’s pumped below comes from local aquifers. Powertech’s permit calls for taking 3 million gallons of water every day from this semi-arid area, which has recurring cycles of drought.

“The proposed water usage is absurd,” says Clean Water Alliance spokeswoman Rebecca Leas.

After the uranium has been removed from the liquid, the excess, which now contains toxic heavy metals and radiation, is pumped back into the ground or sprayed on the surface. “This is a form of mining that always contaminates, and it’s done right in the water supply,” says environmental attorney Bruce Ellison of Rapid City, S.D.

Of course, the mining company says that the layers of rock above and below the uranium-bearing strata are impervious, as dense as if they formed a triple-sealed, underground storage tank. How could anything leak out of solid rock?

Then I think of Jewel Cave and its 166 miles of passages snaking underneath only six square miles of land, and the memory shoots holes through the “solid rock” idea. It makes me wonder how Powertech can claim that radioactive liquids won’t get into the aquifers where drinking water comes from.

I’m well aware that different strata of rock have different characteristics and that some are denser than others. But even if a rock layer has been virtually impenetrable in the past, there is no guarantee that it will remain so in the future.

Our planet’s current form is neither solid nor permanent. It’s in a constant state of flux. It is subject to internal and external forces. Groundwater and gravity team up to exploit and penetrate the tiniest crack or weakness in an “impenetrable” rock layer. The wells that Powertech drills will also connect previously separated layers of rock, providing a way for radioactive water to get where it’s not supposed to go. The history of in-situ uranium mines in Wyoming, Nebraska and Texas shows that this is exactly what happens.

The problem is that humans looking to turn a profit make ridiculous promises that distort or ignore science, history and common sense. Remember the Deepwater Horizon oil rig that British Petroleum claimed could not fail, or the West, Texas, fertilizer plant that couldn’t explode, or the earthquake-proof Fukushima nuclear power plant that continues to spew radioactivity today?

When dealing with the forces of nature, there are no 100 percent ironclad guarantees. Anyone who offers such rock-solid assurances is merely peddling snake oil and should not be trusted.

Ken Steinken is a contributor to Writers on the Range a service of High Country News (hcn.org). He writes about nature and the environment in Rapid City, South Dakota.