Here’s the release from the Colorado Geological Survey (Matt Sares):
Is high, pristine mountain water always clean and pure? Can streams unaffected by human activities and livestock influences be unfit for human consumption, or fish? A new study by the Colorado Geological Survey (CGS) has some surprising answers. The study examines specific areas in Colorado that have naturally poor, surface-water quality due to the area’s geology.
The report, titled “Natural Acid Rock Drainage Associated with Hydrothermally Altered Terrane in Colorado,” identifies a number of streams in eleven different headwater areas of Colorado where surface water is acidic and has high concentrations of metals upstream of any significant human impacts.
Rocks in these areas were altered by intensely hot water circulating in the earth’s crust, often associated with volcanic activity during Colorado’s geologic past. The “hydrothermal alteration” of the rocks changed their composition by dissolving some minerals and depositing others. In the affected areas, the hydrothermal-alteration process deposited metal-sulfide minerals, commonly pyrite (fool’s gold), in the rocks.
When these rocks are exposed at the surface, they interact with oxygen and the iron sulfide “rusts” to form iron oxide minerals, creating striking yellow, orange, and red colors – similar to the oxidation of metal in an old rusty car. “Acid rock drainage” occurs when the sulfur that is displaced by the oxygen combines with water to form weak sulfuric acid. The acidic water then dissolves minerals from the bedrock, often adding significant amounts of dissolved metals to these headwater streams. Natural acid rock drainage has been active in Colorado for thousands, possibly millions of years.
More coverage from the Associated Press (Catharine Tsai) via The Columbus Republic. From the article:
The agency launched the study after working with the U.S. Forest Service to identify Environmental problems related to abandoned mines. Former Colorado Geological Survey Deputy Director Matt Sares says that during that work, researchers found that water upstream of mine sites wasn’t always as pristine as researchers thought it would be.
The Colorado Geological Survey’s new study identifies streams in 11 headwater areas where surface water is acidic and has high concentrations of metals even upstream of any significant human impacts.
More water pollution coverage here.