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Environmental Health - Toxic Substances


Hardrock Mining in Rocky Mountain Terrain -- Upper Arkansas River, Colorado [Completed]

Electron photomicrograph of aggregated hydrous ferric oxide.
Electron photomicrograph of aggregated hydrous ferric oxide, which is commonly found in streams affected by acidic, metal-rich waters. Colloidal iron particles range in size from one nanometer (see detail photo on right) and aggregate to particles greater than 1 micron. This large range of particle sizes poses a problem in defining "dissolved" metal concentrations because the smaller colloidal particles can pass through a 0.45 micrometer filter, which is the filter size usually used to define dissolved concentrations. In order to facilitate geochemical modeling, USGS scientists have studied filtration methods that allow better definitions of that is truly dissolved.

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Mined watersheds in the Rocky Mountains are characterized by high altitudes, significant runoff and numerous contaminant sources dispersed through the watershed. Research on hardrock mining contamination in Rocky Mountain terrain is focused in the Arkansas River Basin. Acid mine drainage containing metals enter streams via runoff from mine wastes and tailings and ground-water pathways. The metals and acidic conditions are toxic to aquatic life. Scientists have studied contaminant source mechanisms, transport and transformation in streams, and how to use this knowledge to determine effective remedial strategies.

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