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).
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.
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.
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 that reference work by the USGS
on the hyporheic zone, transient storage, and/or the solute transport modeling code OTIS
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 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.
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.
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, Colorado, 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 (upper left) mixes with the waters of the Animas River, Colorado (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, Colorado. Reactions in mixing zones affect the transport of metals for hundreds of kilometers downstream.
Scenic view of the Upper Animas River watershed, Silverton, Colorado -- 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, Colorado.
scientists processing water samples during a stream tracer test on California Gulch, Upper Animas River watershed, Colorado.
Collecting fish samples for toxicity testing with an electrofishing unit in the Upper Animas River, Colorado.