Acid Rock Drainage: The Next Focus of Environmental Regulation?
Acid Rock Drainage is acidic water caused by surface or groundwater coming in contact with sulfide materials in the presence of oxygen. It may be natural or caused by human activity; mining can increase or accelerate the formation of ARD by exposing large volumes of sulfide-rich material to weathering. Waters affected by ARD often have pH of less than 5.5, and may contain elevated levels of metals and sulfates. The presence of acidity and metals renders ARD-affected waters inhospitable to aquatic life, and may make affected waters unsuitable for other uses if not treated.
 Scope of the Problem
[a] Geographic Areas Affected
It is difficult to quantify the geographic area affected by ARD. This is partly because stream mileage and water quality data are not consistently inventoried and reported, and partly because it is hard to separate natural effects from humancaused ones. ARD is present in some form in most mineralized areas of the Sierras, the northern and southern Rockies, and to a lesser extent in the Basin and Range. It is also present in the eastern coal fields. Many hundreds to possibly several thousand stream miles are potentially affected to varying degrees.
[b] Close Association of Economic Mineralization with Potentially Acid Generating Mineralization
ARD is a problem for the mining industry because the sulfide minerals
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