Springs good for bathing, bad for radioactive waste
Deserts, by definition, are dry. But some parts of a desert are drier than others.
The paucity of rain has driven desert plants to evolve two major strategies for collecting water. Some plants, such as cacti, keep their roots near the surface, where they can suck up rainwater as soon as it enters the ground.
Other plants take advantage of water deeper down. “Phreatophytes” (“well plants”), such as mesquite, grow in the dry washes; their roots go down deep to collect the water that’s funneled between the rocky slopes.
Observing what’s growing where, we can use plants as “rain gauges” to determine whether water is near the surface, or might be found down deep.
I made a short pack trip not long ago in the mountains of southern Nevada, 80 or so miles north of Las Vegas. Southern California’s Mojave Desert intermingles here with the high desert of the Great Basin. The cooler ridge tops favor vegetation of the Great Basin; the warmer valleys, vegetation of the Mojave.
It is in the dry washes of the valleys that one would expect to find phreatophytes. But they’re not here. The water table in this part of the desert lies too deep even for the roots of phreatophytes – a thousand or so feet beneath the surface.
Climbing up to the ridge-top, I lay out my sleeping bag for a night under the stars. At the head of the bag, I place the items I might want before dawn: flashlight, canteen, midnight snack, Geiger counter.
My campsite lies on the extreme western edge of the Nevada Test Site, Ground Zero for more than 700 nuclear explosions (the fallout from which is still blowin’ in the wind). Within the next decade, this mountain could become the world’s first permanent repository for high-level nuclear waste – mostly spent fuel off-loaded from nuclear power plants across the nation.
Nuclear waste must remain where it’s put. The most likely way to mobilize waste is with water. The primary attraction of Yucca Mountain as a repository site is the great depth to groundwater.
Will the water always stay so deep?
Water rarely flows in “underground rivers.” Rather, it seeps though cracks and pores in the rock. Squeeze those cracks and pores, and the water squirts out … and up. Earthquakes squeeze rock, and could thus push water toward the surface: “seismic pumping.”
Geologist Jerry Schmansky believes a powerful earthquake could send groundwater upward, into the waste repository, and perhaps to the surface.
As I roamed the mountain with him one day, Schmansky pointed out deposits of travertine – limestone deposited where, in times past, groundwater had reached the surface in hot springs. Other geologists, however, argued that the carbonates within the mountain had been deposited, not by groundwater moving up, but by rainwater leaching down.
Geochemist Jean Cline recently completed a project to settle the issue. Groundwater has, indeed, risen upward through the mountain … but so long ago that it’s unlikely to happen again.
Travertine is one of a number of features that have triggered concern about the ability of Yucca Mountain to retain nuclear waste. Many other concerns remain … so many, in fact, that the U.S. General Accounting Office has labeled any decision on the project as premature.
Despite that, President Bush, acting on the advice of his secretary of energy, has decided to make Yucca Mountain the repository site. The state of Nevada will register its opposition in the near future; it will then be up to Congress to decide the fate of the mountain.
Trained as a biologist, Alan Stahler is also an amateur astronomer. He teaches biology and geology at Bitney Springs Charter High School. His science programs can be heard at noon on alternate Tuesdays on KVMR-FM (89.5).
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