The legacy of mining pollution at Leadville, Colo. Blue, purple and yellow show minerals that cause dangerous acid mine drainage carrying cadmium, zinc and lead. Green shows less-hazardous minerals; red and orange show minerals that contribute little to water contamination. Courtesy U.S. Geological Survey and U.S. Bureau of Reclamation.
More eyes than a house fly
Leadville, Colo., is the highest municipality in the country. This impoverished town is also one of the most polluted -- it's located entirely inside the 16.5 square-mile California Gulch Superfund site.
|One hundred thirty years of mining produced an estimated $12.5 billion (in 1997 value) of lead, silver, zinc and gold, according to the Colorado Geological Survey. The miners also left innumerable piles of waste rock that are leaching acids and heavy metals into the watershed, contaminating groundwater and surface water.|
Photos courtesy FourteenerNet, Guide to Central Colorado's Fourteener Country.
"There are hundreds of waste rock piles" in just one unit of the Superfund project, says Ron Pearson, a U.S. Bureau of Reclamation geologist, and "some are actively oxidizing and some are not."
Oxidization is a step that breaks down the mineral pyrite -- a common component of the waste piles -- and makes raw material for sulfuric acid. Sulfuric acid is the major problem, since it mobilizes heavy metals -- allowing them to move downhill -- in a dangerous slop called acid rock drainage. Thus the cleanup effort must isolate the pyrite-containing piles from the environment.
Fixing the worst problems first
In 1996, the U.S. Bureau of Reclamation found such a money-saver in a high-tech camera, built at NASA's Jet Propulsion Laboratory, that makes images containing an enormous amount of information. The machine, called Airborne Visible-Infrared Imaging Spectrometer (AVIRIS), measures 224 wavelengths of light for each point in the image, including both visible light, and the longer wavelength infra-red light adjacent to the visible spectrum. (Confused by this spectrum business?)
AVIRIS flies at 12 miles above the surface in a 500-mph U2, a spy plane that's been modified to do environmental research. After it gathers data on an 11-kilometer-wide strip of land, a computer processes the data and makes maps showing which minerals are predominant on the surface of the ground (one such map is shown above).
In Leadville, these maps pinpoint the sources of the worst contamination and can be used to guide the cleanup. Within six months of operation, AVIRIS returned results that would have cost $2-million and taken at least two years with conventional techniques, Pearson says. Ground samples -- taken to verify that the spectrometer was reflecting reality -- proved that the spectrometer was "very accurate," he adds. And while the spectrometer can only read light reflected by minerals on the surface, those were the major concern in Leadville.
How can a picture detect metal?
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