Environmental occurrence and impacts of arsenic at gold mining sites in the western United States

Arsenic is a common element in the natural environment and is frequently a significant component in gold deposits of the western United States. Such deposits contain various forms of arsenic: arsenides, sulfides, and sulfosalts. Upon weathering such minerals routinely lower the pH of nearby waters, mobilizing arsenic and other metals. Arsenic may also be mobilized in aqueous environments where cyanide has been used to leach gold ores, resulting in high water pH. Incorrect construction of monitoring wells can result in contamination by cement/grout, which may raise pH causing arsenic concentrations to appear inordinately elevated.