Tailings piles, such as this one in California Gulch, Colo., are a source of metal-rich, acidic water in the upper Arkansas River Watershed, Colo. USGS scientists studied the occurrence of toxic metals in water, colloids, and bed sediments in the Arkansas River downstream from it's confluence with California Gulch.

Drainage from abandoned mine wastes, such as this embankment along the side of California Gulch, Colo., can cause potential harm to fish not only adjacent to the wastes but for many miles downstream as well.

USGS scientists conducted a diel (daily cycles) study of Arkansas River, Colo., and its tributary California Gulch, Colo. (in photo), to identify potential photoreduction of iron. The transport of iron in metal-enriched streams is controlled by photoreduction, precipitation, and dissolution

Acid mine drainage from California Gulch (right) mixes with the waters of the Arkansas River, Colo. (left). The Gulch was a source of hydrous iron oxides that precipitated as colloids and moved in suspension down the Arkansas River. Historic surges from mine works have released much larger plumes into the Arkansas River that have been visible for miles downstream.

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

Tangential flow filtration equipment used to study iron and aluminum colloids in streams affected by mine drainage. Understanding the formation and transport of colloids can help understand the movement and storage of contaminants, which is information environmental professionals can use to design more cost effective cleanup programs

Ultrafiltration allows the study of metals transported by colloids in streams affected by mine drainage. The photo shows a raw sample from California Gulch, near Leadville, Colo. (left), the clear ultrafiltrate (center), and the concentrate of colloids for analysis (right). Without ultrafiltration scientists would not be able to collect enough sample to analyze

USGS scientists inject tracers, such as lithium chloride in this case, into mountain streams to learn more about stream hydrology and chemistry than can be gained from traditional discharge and water-quality measurements. The methods they are developing to characterize contaminated streams can be used by water-resource managers to make better cleanup decisions

The large white bottle contained a solution of sodium bromide, a conservative tracer, that was injected into the stream to characterize the hydrology of St. Kevin Gulch, Colo.Ña stream impacted by acid mine drainage. The analysis of tracer injection experiments can yield a wealth of hydraulic information, for example information on time of travel, instantaneous discharge, temporal variation in discharge, and rates of ground-water inflow

The site where a tracer, sodium bromide in this case, was injected into St. Kevin Gulch, Colo., to study the processes that control the transport of metals in mining impacted streams. The small platform on the left side of the stream holds the equipment used to inject the tracer solution into the stream. Tracer tests are one way scientists use to study the effects of back storage on the transport of contaminants in mountain streams

USGS scientist collecting a water sample from St. Kevin Gulch, Colo., during a tracer injection experiment. Water-quality monitoring data collected during the experiment is use to characterize both flow in the stream channel and associated flow in bed sediments below the stream channel

USGS scientist collecting a water-quality sample during a tracer injection experiment along a segment of St. Kevin Gulch, Colo. The black cylinder to the left of the scientist is an auto sampler used to collect water samples at frequent time intervals

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)