Uranium discovered in Colorado’s Chimney Hollow Dam, the largest built in United States in 20 years

By Dillon Thomas

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    Colorado (KCNC) — Just weeks before completion of construction, Northern Water has confirmed uranium has been discovered at the site of the Chimney Hollow Reservoir and Dam. The project, which is expected to serve more than 1 million Colorado residents, has been in the making for decades.

For many, uranium is typically associated with nuclear weapons and power. The radioactive element was first detected at the end of 2024, however Northern Water was unable to determine the source of the uranium until recently.

Now they know. It’s coming from the rocks they used to build the 350-foot dam, which were mined from the very land they plan on flooding with water.

“As we were building this dam, we were using rocks that were quarried on-site,” said Jeff Stahla, spokesperson for Northern Water.

CBS News Colorado’s Dillon Thomas was taken into the project zone in 2024 where dozens of large trucks could be seen mining rock from the bottom of the future-reservoir. Trucks were moving more than 62,000 tons per day from the quarry to the dam.

Now near-complete, the Chimney Hollow Dam is the fourth largest dam in Colorado and the largest built in the United States since the year 2000.

Northern Water is now working with the Environmental Protection Agency to monitor the levels of uranium being detected. Stahla said the water supplier wanted to be transparent with the community as quickly as they could be.

“We are looking to be finished with construction in the next six weeks. As we started to consider filling the reservoir, we wanted to make sure the public was aware of some of the conditions we found and that we are going to address them,” Stahla said.

Northern Water currently plans to begin filling the reservoir in August. Stahla said the discovery of the uranium is not enough to derail the project.

“The concern about uranium is not about radioactivity or things people often associate with uranium. But, it is from the standard of long term ingestion,” Stahla said.

Stahla said the company is considering their options moving forward. Those include treating the initial fill of the reservoir or allowing the water to naturally do the work for them.

Citing the reservoir’s eventual capacity of hundreds of billions of gallons of water, Stahla said there is a possibility the initial fill of the reservoir will wash the uranium off the dam and dilute it. Eventually, as water cycles in and out of the reservoir, the concern of the uranium may not longer be an issue.

“It is a strong possibility that these mineral levels will decrease far below the standards set by the EPA,” Stahla said.

Northern Water said they will continue to monitor the uranium levels moving forward and will work with health agencies to assure the drinking water that will one day fill the reservoir will be safe for consumption.

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