Vogel Canyon spring in the Purgatoire River Basin, Otero County, Colorado, May 2007. Photo credit: Larry Scott for the CGS.

Surface Water Quality

As snowmelt and rain enter Colorado streams and percolate into the ground, the water picks up particles and dissolves some components of the rocks. Ordinarily, this natural process does not affect the water quality enough to be of concern. However, in some areas elements in the rocks are dissolved in high enough concentrations to adversely affect the bio-system.

Pierre Shale (gray) exposed along St. Vrain Creek in Weld County, Colorado. Photo credit: Stephen Keller for the CGS.
Pierre Shale (gray) exposed along St. Vrain Creek in Weld County, Colorado. Photo credit: Stephen Keller for the CGS.

Humans are major water polluters around the globe. However, natural groundwater movement also causes significant water contamination globally—including salts, acids, radioactivity, nitrogen, along with metals—arsenic, selenium, zinc, lead, iron and manganese. As we attempt to regulate and clean up human pollution of water, it is important to recognize natural water pollution sources in a particular area. Understanding the geology of an area is important to aid in recognizing potential natural sources of water pollution.

IS-12 Hydrogeologic and Stratigraphic Data Pertinent to Uranium Mining, Cheyenne Basin, Colorado, a 1979 report, looks at natural groundwater contamination near a proposed in-situ uranium mine in Weld County.

Another related CGS publication is the award-winning study B-54 Natural Acid Rock Drainage Associated with Hydrothermally Altered Terrane in Colorado that reveals the geology behind poor water quality in a number of areas of Colorado. It identifies and examines streams in eleven different head water areas of Colorado where surface water is acidic and has high concentrations of metals upstream of any significant human impacts.

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