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Contamination Associated with Active and Abandoned Hard-Rock Mining

Mineral Creek, Colo., with drive point wells along the length of the creek.
A field experiment in Mineral Creek, Colorado, used 18 drive point wells along a 33-meter study reach to sample for groundwater inflow to the stream of metal-rich water (copper, zinc, and other metals) from abandoned mine sites. Identification of such inflows, when no surface manifestation occurs, is one of the applications of stream-tracer injections.

USGS scientists in protective gear.
USGS scientists display some of their precautions used to prepare a sodium hydroxide solution. The solution was used for a pH modification experiment in Mineral Creek, Colorado. The pH modification experiment was designed to study the changes in geochemical conditions that affect the transport of metals in streams during remediation of acidic mine drainage.

USGS scientist with two large white plastic tanks containing a sodium hydroxide solution.
Solutions of lithium bromide (right tank) and sodium hydroxide (left tank) used for of a pH-modification experiment in Mineral Creek, Colorado. The experiment was designed to simulate remediation of acid mine drainage systems that artificially raise the pH of streams.

View of Mineral Creek, Colo. Two two large white plastic tanks are on the right streambank.
Green ferrous iron hydroxide precipitate forming downstream from the injection of sodium hydroxide base (white tubing in stream) into metal-rich, acidic Mineral Creek, Colorado. The injection of the base solution is an analog for mine drainage cleanup programs that use limestone and other materials to raise the pH of streams to conditions that support fish habitat.

A white tube running from a large white tank to the streambed of Mineral Creek, Colo.
A field experiment in August 2005 tested the injection of sodium hydroxide base into the metal-rich, acidic (low pH) Mineral Creek, Colorado. Green ferrous iron hydroxide precipitate formed downstream from the injection point (white tubing in stream). A reactive solute-transport model, OTEQ, was used to predict the changes that occurred in the acidic stream when the pH is raised by the injection of the high pH solution (basic solution).

A streambed heavily coated with yellow aluminum and iron precipitates.
Before a pH modification experiment conducted in Mineral Creek, Colorado, the pH of the stream was about 3.0, and the streambed was heavily coated with aluminum and iron precipitates. Mineral Creek receives acid mine drainage from abandoned mine lands and is one of the streams that USGS scientists are studying to understand the factors that influence the transport of metals in acidic streams.

A streambed coated with brown ferrous iron hydroxide precipitates.
During a pH modification experiment conducted in Mineral Creek, Colorado, the pH of the stream changed from about 3.0 to about 8.0 (acidic to mildly basic). The change in pH caused the older precipitates in the stream to be covered by a new precipitate (ferrous iron hydroxide). A solution of a base (sodium hydroxide) was injected into the stream to change the pH.

USGS scientists collecting water-quality samples from drive point wells.
USGS scientists collecting water-quality samples from drive point wells along a 30-meter reach of Mineral Creek, Colorado. The wells were located near pits along the streambed to characterize the quality of groundwater entering the stream.

Graph of the increasing number of papers in hydrology journals.
Graph of the increasing number of papers in hydrology journals that reference work by the USGS on the hyporheic zone, transient storage, and/or the solute transport modeling code OTIS.

Diagram of biological processes from sources to receptors in the streams.
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.

View of Red Mountain No. 3, near Silverton, Colo.
One of the basic questions for understanding contamination from hardrock mining relates to mined versus unmined sources of metals. This view of Red Mountain No. 3, near Silverton, Colorado, 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.

USGS scientists examining and iron bog along Red Mountain Creek, near Silverton, Colo.
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 groundwater discharging into the stream, to large seeps from iron bogs such as the one shown in this view along Red Mountain Creek, near Silverton, Colorado.

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Page Last Modified: Wednesday, 07-May-2014 14:44:31 EDT