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In the western United States, a toxic relic of World War II and the Cold War remains: radioactive groundwater caused by former uranium ore mining and processing sites. Seven of these sites are found along Colorado’s western slope, and engineers at the CU Boulder are testing out a new technique to clean them up.

Professor Roseanna Neupauer of CU Boulder and Professor David Mays of CU Denver have created a process called Engineered Injection and Extraction, which has shown promising results in removing other contaminants. But uranium, which readily shifts between different oxidation states, has historically proven trickier.

Starting in the 1940s, nuclear weapons development drove uranium mining in the U.S. The process stripped uranium from rock, processed it into a powder and left behind vast piles of radioactive rock, or tailings. Many mines ceased operations by 1978, but officials didn’t remove the tailings until much later.

“This isn't necessarily as local as, say, a gas station tank that ruptures in the middle of the city, which has the possibility of endangering water supplies for large amounts of people—these places can be remote,” said Jack Greene, a graduate student in the .