Conceptual diagram of biological processes from sources to receptors in the catchment, stream system. Metal sources from the watershed are transported to the aquatic ecosystem in water and sediments. Within the aquatic ecosystem, these metals then affect organisms within the food web

One of the basic questions for understanding contamination from hardrock mining relates to mined versus un-mined sources of metals. This view of Red Mountain #3, near Silverton, Colo., shows the complex nature of the problem. Extensive alteration of bedrock can produce acid rock drainage, while mines, like the Yankee Girl mine shown here (lower half of photo), dot the terrain producing acid mine drainage

An important part of quantifying the loading of metals to streams is to identify and characterize inflows along the stream. Inflows can range from dispersed seeps, to subsurface inflow from ground-water discharging into the stream, to large seeps from iron bogs such as the one shown in this view along Red Mountain Creek, near Silverton, Colo.

A USGS scientist and a volunteer sample metal-rich water from a seep draining a pile of mine tailings along Silver Creek, near Park City, Utah. Seeps such as this one can come from tailings piles that are remnants of past mining activities. Contaminants from hardrock mining can come from adits, waste rock piles, and from tailings that were stored along streams

Cement Creek, Colo., is a site of USGS investigations of the fate of acid mine drainage. USGS scientists are developing methods to characterize contaminated streams that can be used by water-resource managers to make better cleanup decisions

Acid mine drainage from Cement Creek (left) mixes with the waters of the Animas River, Colo. (right) in 1997. Chemical reactions creating the yellow and orange colloids in this mixing zone affect the transport of contaminants down the Animas River

Detailed vertical sampling across a mixing zone as acid, metal-rich water from Cement Creek (left) joins near-neutral water of the Upper Animas River (right), near Silverton, Colo. Reactions in mixing zones affect the transport of metals for hundreds of kilometers downstream

Scenic view of the Upper Animas River watershed, Silverton, Colo. -- one of the watersheds in the USGS Abandoned Mine Lands Initiative

A small mountain stream impacted by acid mine drainage, Prospect Gulch, Upper Animas River Watershed, Colo.

USGS scientists processing water samples during a stream tracer test on California Gulch, Upper Animas River Watershed, Colo.

Collecting fish samples for toxicity testing with an electrofishing unit in the Upper Animas River, Colo.

Locating inflows and springs discharging into Mineral Creek, Colo., prior to conducting tracer test. Tracer tests are used to assess the relative magnitude of metal loading from inflows along a stream reach