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.
Metals in Colorado’s mountains sometimes seep into streams from abandoned mines and waste rock piles. In other streams, high concentrations of metals occur naturally as a result of the geology of the area. Acid rock drainage occurs when water and oxygen interact with metal-sulfide minerals, such as pyrite, producing sulfuric acid that dissolves metals and carries them into groundwater and streams.
Naturally occurring uranium deposits within the groundwater zone can also cause contamination. In 1980, the CGS studied natural groundwater contamination in the Cheyenne Basin of Colorado as a baseline for potential in-situ uranium mining. The study of 104 water wells showed significant levels of existing contaminants. Indeed, many of the wells did not meet EPA standards for uranium in drinking water.
High salinity concentrations may also be a cause of degraded water quality. Groundwater and surface water may dissolve ancient sea salt deposits that underlie many parts of Colorado. High selenium concentrations may occur when water dissolves selenium-rich rocks, such as the Upper Cretaceous marine shales that are found in the Gunnison River Basin/Grand Valley area, the Pine River Basin, and the Middle Arkansas River Basin. The geology and water quality of an area should be assessed before any development takes place — this will alert planners to potential problems.
There are numerous stories in the media concerning potential degradation of water quality from hydraulic fracture stimulation (or ‘fracking’) used by the oil and gas industry to obtain commercial quantities of petroleum. The American Association of State Geologists (AASG) released a consensus statement on hydraulic fracturing in July 2012.
Neubert, John T., Jeffrey P. Kurtz, Dana J. Bove, and Matthew A. Sares. “Bulletin 54 – Natural Acid Rock Drainage Associated with Hydrothermally Altered Terrane in Colorado.” Bulletin. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 2011.
Topper, Ralf, and Andy Horn. “WAT-2011-01 – El Paso County Groundwater Quality Study: Phase 1.” Groundwater. Denver, CO: Colorado Geological Survey, Department of Natural Resources, March 2011.
Berry, Karen. “WAT-2005-01 – Turkey Creek Watershed Case Study.” Water. Denver, CO: Colorado Geological Survey and the Jefferson Conservation District, 2005.
Weber, George R., and Matthew A. Sares. “IS-66 Directory of Colorado Water Quality Data.” Water Quality. Information Series. Denver, CO: Colorado Geological Survey, Division of Minerals and Geology, Department of Natural Resources, 2003.
Colorado Geological Survey. “RockTalk V05N4, October 2002 – Ground Water in Colorado.” RockTalk, October 2002.
Colorado Geological Survey. “RockTalk V03N2, April 2000 – Water Quality in Colorado.” RockTalk, April 2000.
White Paper – Abandoned Mines and Naturally Occurring Acid Rock Drainage
Kirkham, Robert M., William O’Leary, and James W. Warner. “IS-12 Hydrogeologic and Stratigraphic Data Pertinent to Uranium Mining, Cheyenne Basin, Colorado.” Information Series IS-12. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 1980.
Colorado Abandoned Mine Land (AML) Information map — May also be accessed through the CDPHE at the Mine Impacted Streams TaskForce. The user interface is a GIS platform and includes AML information layers which can be projected on road maps, satellite imagery, property ownership maps,
watershed maps, and so on.