Northern Water announced Thursday that naturally occurring uranium has been found in rocks quarried at its Chimney Hollow Reservoir construction site, and that the contaminant will leach into the water as the reservoir begins to fill.
The news comes just months before Northern had hoped to begin filling the new storage pool west of Carter Lake in Larimer County.
This Fresh Water News story is a collaboration between »Ê¹Ú²©²ÊÍøÖ· and Water Education »Ê¹Ú²©²ÊÍøÖ·. It also appears at .
“The uranium at Chimney Hollow is naturally occurring in the granitic rock formations that were quarried to supply material for the dam. As the reservoir fills, these rocks will be in direct contact with water, leading to the leaching of uranium into the water. This issue will initially require close monitoring and management when filling Chimney Hollow Reservoir,†the agency said in a statement.
The finding was unexpected, said Northern spokesman Jeff Stahla, especially given that the Windy Gap Project, of which Chimney Hollow is a part, has historically had very clean water from the headwaters of the »Ê¹Ú²©²ÊÍøÖ· River in Grand County on the Western Slope.
Unlike other utilities, such as Denver Water, Northern is a wholesale water provider to northern »Ê¹Ú²©²ÊÍøÖ· cities, which are responsible for treatment. Stahla said project participants have been briefed on the issue and will decide jointly how to move forward.
project will serve 12 »Ê¹Ú²©²ÊÍøÖ· communities, including Loveland, Greeley, Longmont, Lafayette and Louisville. Construction began in 2021.
Northern said it expected the uranium to decrease over time as the uranium bearing rocks are washed by the water flowing in and out of the reservoir. Still, the agency said it would not release water from the reservoir until additional analysis can be done.
The U.S. Environmental Protection Agency regulates uranium in drinking water supplies and limits it to . Stahla said it wasn’t clear how much it would cost to treat and remove the contaminant from the water supply or how long it might delay water deliveries.
Deliveries were supposed to begin in 2027, and Stahla said that might still occur, pending new modeling and analysis of how much uranium seeps into the reservoir.
This kind of uranium is found in different areas of »Ê¹Ú²©²ÊÍøÖ·, and sometimes comes from rocks, mining activities and other sources, according to the »Ê¹Ú²©²ÊÍøÖ· Geological Survey.
Nicole Rowan, director of the water quality control division at the »Ê¹Ú²©²ÊÍøÖ· Department of Public Health and Environment, said there were no concerns about contamination at this time because no water is being delivered yet.
“We are not worried about public drinking water right now because no water has been released,†Rowan said. “And it sounds like it will be several years before any water is released.â€
Rowan said the state is working with Northern to analyze the data and that it will be working with downstream water users in the months and years to come to ensure their tap water will meet safe drinking water standards.