The drainage water from the Iron Mountain Mine is the most acidic water naturally found on Earth; some samples collected in 1990 and 1991 have been measured to have a pH value of -3.6. The drainage water endangers fish, including winter-run Chinook salmon, a federally listed endangered species that spawns in the Sacramento River. Salmon kills have been noted since 1899.
Briefly
Iron Mountain Mine (IMM) has been a source of acid mine drainage resulting from over one hundred years of mining activity. Though mining operations were discontinued in 1963, underground mine workings, waste rock dumps, piles of mine tailings, and an open mine pit still remain at the site. Historic mining activity at IMM has fractured the mountain, exposing minerals in the mountain to surface water, rainwater, and oxygen. The exposed minerals form sulfuric acid, which leaches out copper, cadmium, zinc, and other heavy metals. The resulting acidity and the heavy metal contamination have caused the virtual elimination of aquatic life in sections of Slickrock Creek, Boulder Creek, and Spring Creek, tributaries of the Sacramento River. Since 1940, high levels of contamination in the Sacramento River have caused numerous fish kills. The continuous release of metals from IMM has contributed to a steady decline in the fisheries population in the Sacramento River.
A case study.
[url]http://www.epa.gov/aml/tech/imm.pdf[/url]