Naturally Degraded Waters
Water can be naturally degraded by flowing through saline geologic deposits, such as geologic shallow basin evaporite deposits. This can show up at the land surface as saline springs or deeper in drilled wells.
Waters can also be naturally degraded by acid drainage generated in hydrothermally altered geologic areas. Acid drainage is acidic water (pH <5.0), laden with sulfate and metals that forms under natural conditions when geologic strata containing pyrite are exposed to the atmosphere or oxidizing environments. The typical metals include iron, manganese, aluminum, cadmium, and zinc. The water may be visibly discolored (usually red due to the high iron content). Areas of naturally degraded water commonly have names such as Red Mountain, Red Cone, Iron Creek, and Cement Creek (named for the ferricrete deposits that line its banks).
Hydrothermal activity often creates natural zones of mineral alteration that extend well beyond the immediate location of concentrated ore mineralization. In fact, large areas of hydrothermally altered terrane extend from mined areas to areas without any associated mineral production. Mineral alteration can be a source of hydrologic contamination on a scale that is not immediately evident. Thus, the extent of environmental impact derived from hydrothermally altered areas unaffected by economic mineral production or other significant anthropogenic influence is a subject that historically has not received much attention.
Naturally degraded waters may be unsuited for use in consumption or agriculture due to high salinity or high mineral content. For an award winning CGS study of naturally degraded waters in Colorado, see:
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.” Acid Rock Drainage. Bulletin. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 2011.