A reservoir built to serve nearly a million Northern Coloradans started filling this spring. But Chimney Hollow’s future is still murky weeks after the initial fill.
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Chimney Hollow will eventually pull water from the Colorado River near its headwaters in Grand County to serve a dozen fast growing cities on the Front Range from Broomfield to Greeley.
“Water storage is such a key element of our overall water supply in northern Colorado, and this just adds another increment of that supply to a region where our water demands continue to grow,” Northern Water operations manager Jerry Gibbens said in April as water slowly started filling the reservoir.
But the filling operation stopped 12 days later, way short of its maximum capacity of 29 billion gallons.
Chimney Hollow is holding just 2% of its total volume today because there’s a problem.
Northern Water discovered that some of the rocks it used to build the massive dam at the reservoir contained radioactive uranium. It was naturally occurring, but it set the project back at least a year.
Northern Water is still coming up with a mitigation plan.
“Really, the best way to kind of move that uranium out is to draw down the water and force that out,” spokesperson Rachel Stevens said. “But before we make any of those decisions, we really want to see what the levels of uranium are.”
So every week, crews are taking water samples from the small pool and sending it to a lab to see how much radioactive material is really in the water. The results are expected soon.
Northern Water has only been able to test how uranium leaches out of the rocks in a laboratory setting. Filling the reservoir just slightly will help reveal the extent of the problem.
“None of that water will be leaving until we've got that uranium figured out,” Stevens said.
There are also separate concerns about filling a reservoir with Colorado River water when the waterway is stressed.
Gary Wockner leads a group called Save the Colorado. It sued to stop Chimney Hollow but ended up settling the case and allowing the reservoir to move forward.
“During droughts, the river suffers first and most,” he said. “Any new diversion is going to make this kind of chaos worse.”
Wockner said the reservoir is also risky because it’s a junior water right and there’s lots of uncertainty about who will be forced to cut their water in the future as states remain at an impasse over conservation plans.
He said the diversion to Chimney Hollow will be felt on the Colorado River, where it runs through Grand County.
“Rivers need water, and when you divert water out of rivers, you're causing ecological damage, in this case, in Grand County, severe ecological damage, and in a drought scenario, extreme drought like this one, it just gets worse and worse and worse,” he said.
While Wockner continues his fight to protect fish, willows and the river itself, Northern Water sees things differently. Rachel Stevens said it’s low snowpack years, just like this one, that will make the reservoir more valuable to Front Range residents.
“We need Chimney Hollow, so that when we do have these dry years, we'll have that water supply and be able to continue to deliver that water and have a firm yield even when there's a drought,” she said.
Northern Water won’t say when the reservoir will be ready to start filling taps along the Front Range. Broomfield is the biggest stakeholder in the project.
The city declined an interview request from KUNC News to talk about the reservoir and the uranium complications. Spokesperson Julie Story said in an emailed statement that discussions about how to address the uranium problem will likely take "several months, if not longer."
“From the City and County of Broomfield’s perspective, the current timeline delay does not create a significant operational impact,” Story said. “Given existing drought conditions and hydrologic realities, (Broomfield) would not have been in a position to utilize or fill additional supplies from the project this year regardless.”
