DENVER (AP) — Beneath the western United States lie thousands of old mining tunnels filled with the same toxic stew that spilled into a Colorado river last week, turning it into a nauseating yellow concoction and stoking alarm about contamination of drinking water.
Though the spill into the Animas River in southern Colorado spill is unusual for its size, it's only the latest instance of the region grappling with the toxic legacy of a mining boom.
Until the late 1970s there were no regulations on mining in most of the region, meaning anyone could dig a hole to search for gold, silver, copper or zinc. When mines are abandoned they fill with groundwater and snowmelt that becomes tainted with acids and heavy metals which can trickle into waterways. Experts estimate there are 55,000 such abandoned mines in the region.