July 16, 1979
The largest release of radioactive material in the U.S. occurred in the Navajo Nation. More than 1200 metric tons (1,100 tons) of uranium tailings (mining waste) and 378 million liters (100 million gallons) of radioactive water burst through a packed-mud dam near Church Rock, New Mexico. The river contaminated by the spill, the Rio Puerco, showed 7,000 times the allowable standard of radioactivity for drinking water downstream from the broken dam shortly after the breach was repaired. A month later, only 5% of the tailings had been cleaned out. Warnings not to drink the contaminated water were issued by officials, but non-English-speaking Navajo never heard them, having no electrical power for TV or radio. Humans and livestock continued to drink the water.
