USGS scientists processing water-quality samples during a tracer injection experiment in St. Kevin Gulch, Colo. During stream tracer injection experiments water-quality samples are collected at frequent intervals to observe the change in tracer concentration as the tracer moves downstream

In many cases it is hard to accurately measure the discharge of small mountain streams, such as St. Kevin Gulch, Colo., using standard techniques. Tracer injection experiments that involve the injection of tracers and monitoring their transport downstream allows for the accurate computation of stream discharge

An autosampler was used to collect frequent water-quality samples during a tracer injection experiment on St. Kevin Gulch, Colo. The frequent samples allowed for the accurate simulation of reactive-solute transport processes in the stream. The streambed is yellow-orange in color due to the perception of ferrous iron from the acidic waters caused by acid mine drainage

USGS scientists collect a variety of environmental samples to study the fate and transport of metals in mining impact streams. In the foreground are two sample bottles of fine-grained bottom sediment from pooled areas and bars that were sieved through a nylon 60-µm (micrometer) screen for the analysis of metal concentrations

A light probe (back wire coming up from the bottom of photo) was used to measure light intensity during an investigation of the photoreduction of iron and other metals. Photoreduction caused diel (daily) variations in the concentrations of ferrous iron (Fe II) in St. Kevin Gulch, Colo.

An accumulation of floc in a seep at an abandoned mine site in the St. Kevin Gulch Watershed, Colo. The floc is mostly hydrous oxides of iron but it also contains high concentrations of toxic heavy metals such as arsenic, copper, and zinc

St. Kevin Gulch, near Leadville, Colo., is a field research site where USGS scientists studied the physical, chemical, and biological processes in mountain stream affected by acid mine drainage. This is a downstream view of St. Kevin Gulch as it flows beside a pile of mine waste

An abandoned mine shaft leaking acidic, metal rich water in the St. Kevin Gulch Watershed, Colo. USGS scientists have studied the processes that case spatial and temporal variability of metal concentrations in the watershed's streams

Old mine workings at an abandoned mine site in the St. Kevin Gulch Watershed, Colo. Acid mine drainage from abandoned mine lands affects numerous streams in the western United States and in many other areas throughout the world

The confluence of St. Kevin Gulch (left) and Shingle Mill Gulch (upper middle), Colo. St. Kevin Gulch is orange because it receives acid mind drainage from abandoned mine sites in the watershed. Understanding how inflows from cleaner streams, such as Shingle Mill Gulch, affect the transport of metals downstream will help develop better cleanup programs

Springs in abandoned mine lands can have high concentrations of metals, such as this one in the St. Kevin Gulch Watershed, Colo. The yellow-orange color is due to iron hydroxide precipitates from the acidic, metal-rich water in the spring

A USGS scientist collects a water sample from a spring at the base of a waste rock pile at an abandoned mine site in the St. Kevin Gulch Watershed, Colo. Springs from mine wastes can have high concentrations of cadmium (Cd), copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn)

USGS scientists collect a sediment sample during a study of the chemical processes in streams affected by acid mine drainage in the Upper Arkansas River Watershed, Colo. The study focused on the mixing zones where streams affected by acid mine drainage discharged in to the Upper Arkansas River

One of the sampling stations in a sampling network in the Upper Arkansas River Watershed, Colo., used to study the transport of metals down the river. The gaging station at this site was used to provide data for the calculation of meals loads in the river (Arkansas River near Malta, Colo., Station ID 07083700)