DENVER – 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 is unusual for its size, it’s only the latest instance of the region grappling with the legacy of a centuries-old mining boom that helped populate the region but also left buried toxins.
Until the late 1970s there were no regulations on mining in most of the region, meaning anyone could dig a hole where they liked and search for gold, silver, copper or zinc. Abandoned mines fill up with groundwater and snowmelt that becomes tainted with acids and heavy metals from mining veins which can trickle into the region’s waterways. Experts estimate there are 55,000 such abandoned mines from Colorado to Idaho to California, and federal and state authorities have struggled to clean them for decades. The federal government says 40 percent of the headwaters of Western waterways have been contaminated from mine runoff.