On 16 July 1979 the UNC Church Rock tailings dam failed, releasing ~94–100 million gallons of acidic radioactive mill liquor and ~1,100 tons of solids into the Rio Puerco through Navajo Nation lands. Official packets stressed limited human doses; NRC/EPA records show the largest U.S. uranium-mill liquid release by volume, Superfund longevity, and chronic mine-dewatering as a co-equal long-term pathway.