MAPPING MINE WASTES AND PREDICTING AREAS AFFECTED BY SELENIUM-RICH WATER RUNOFF IN SOUTHEAST IDAHO USING AVIRIS DATA, AND DIGITAL ELEVATION MODELS

Waste rock from phosphorite mining in Southeastern Idaho contains trace amounts of selenium, cadmium, and vanadium. Selenium concentrations in the hundreds of ppm have been found in rocks, soils, plants, and streams near some mine waste dumps, and recent mortality of livestock due to selenosis poisoning has been linked to water and vegetation contaminated by mine waste. The dispersal of selenium into the environment is complex. For example, the South Maybe Canyon watershed has a mean selenium concentration of 751 mg/l (surface water samples) in contrast to Angus Creek watershed, which has a mean selenium concentration of 3 mg/l. Both watersheds are fed by seeps at the base of large mine waste dumps. Plants growing on both dumps contain selenium concentrations of 100-500 ppm.

Airborne Visible-Infrared Imaging Spectrometer (AVIRIS) data were used to remotely map mine waste and vegetation. Spectral units, defined from AVIRIS data, were combined with a digital elevation model (DEM) in order to identify areas that need remediation. Mine waste and lithologic spectral units were used to define mine dumps. Vegetation spectral units were used to discriminate between land-cover types such as pastureland. Mapped mine waste dumps and riparian vegetation were registered to digital elevation data to determine (1) total watershed areas above individual dumps, (2) flow direction from the dumps, (3) stream gradients, and (4) the extent of downstream wetlands available for absorption of selenium by organic mat. Results indicate that areas of most severe selenium contamination such as the South Maybe Canyon watershed tend to be associated with larger areas of watershed upstream from mine dumps. These larger areas channel greater volumes of surface water through mine dumps. In addition, higher stream gradients inhibit selenium reduction and fixation, and a paucity of wetlands aid in selenium retention.