In America’s rush to build the nuclear arsenal that won the Cold War, safety was sacrificed for speed.

Uranium mills that helped fuel the weapons also dumped radioactive and toxic waste into rivers like the Cheyenne in South Dakota and the Animas in Colorado. Thousands of sheep turned blue and died after foraging on land tainted by processing sites in North Dakota. And cancer wards across the West swelled with sick uranium workers.

The U.S. government bankrolled the industry, and mining companies rushed to profit, building more than 50 mills and processing sites to refine uranium ore.

But the government didn’t have a plan for the toxic byproducts of this nuclear assembly line. Some of the more than 250 million tons of toxic and radioactive detritus, known as tailings, scattered into nearby communities, some spilled into streams and some leaked into aquifers.

Congress finally created the agency that now oversees uranium mill waste cleanup in 1974 and enacted the law governing that process in 1978, but the industry would soon collapse due to falling uranium prices and rising safety concerns. Most mills closed by the mid-1980s.

When cleanup began, federal regulators first focused on the most immediate public health threat, radiation exposure. Agencies or companies completely covered waste at most mills to halt leaks of the carcinogenic gas radon and moved some waste by truck and train to impoundments specially designed to encapsulate it.

But the government has fallen down in addressing another lingering threat from the industry’s byproducts: widespread water pollution.

Regulators haven’t made a full accounting of whether they properly addressed groundwater contamination. So, for the first time, ProPublica cataloged cleanup efforts at the country’s 48 uranium mills, seven related processing sites and numerous tailings piles.