Opinion: Will we have more uranium in our water?

I recently read about the Northern Colorado Water Conservancy District’s discovery of uranium in the rocks in the just-completed Chimney Rock Reservoir. 

For background, the Colorado-Big Thompson system (built by the Bureau of Reclamation) was started in the 1930s, some years after the 1922 Colorado River Compact was signed. The C-BT delivers water from the upper Colorado River to cities and farms in the northern Front Range, including Boulder.

Much later, Northern built the much smaller Windy Gap reservoir on the Colorado, completed in 1985, which Boulder and other Front Range cities bought into. Windy Gap’s water rights are junior to the C-BT, which is junior to the Compact. Colorado River water constitutes about a third of Boulder’s supply.

Northern apparently contemplated early on the idea of building a reservoir on the Front Range to store the water collected in Windy Gap and piped across the mountains. This led to the construction of the Chimney Hollow Reservoir, beginning in 2021 in the foothills of the Front Range, just west of Carter Lake Reservoir and over one ridge.

Suddenly, a couple of years ago, Northern announced that it had discovered uranium in the rock in the reservoir. Northern’s Chimney Hollow Reservoir Project web page is guardedly optimistic: “This issue will require close monitoring and management when filling the reservoir, as these rocks will be in direct contact with the water and leaching of uranium will occur. The leaching process is expected to decrease over time, although it is currently uncertain how long it will take. Staff and project participants are working diligently to collect data and investigate operational strategies to mitigate this temporary challenge. No water will be delivered from Chimney Hollow Reservoir until assessments are complete, and a mitigation plan is developed to ensure a safe raw water supply. Dam safety and other tests will continue throughout this process over the next two to three years.”

This situation raises a whole host of questions for me. For starters, didn’t Northern test the area for such contaminants before starting design and construction? And if not, why? Chimney Hollow is located west of the edge of the Front Range, and so was likely to be in granite, versus the sedimentary rock to the immediate east where Carter Lake is. So Northern could not count on the same geochemistry. Northern does acknowledge that “Mineralized uranium naturally occurs in some of Colorado’s geological formations.” Thus, presumably, some testing should have been done early in the design process.

I remember talking with some Northern staff a few decades ago at a public event at the Boulder Country Club. I asked them how Northern saw the potential effects of global warming on its Colorado River water supply. I was quite surprised that there didn’t seem to be serious consideration regarding the impacts of climate change on their ability to deliver water. This was doubly surprising, since Boulder started looking at the effects of climate change years before, in 1987, with its first Raw Water Master Plan. 

That incident did make me wonder about Northern’s strategic management. So, the finding of uranium at this late date in the process didn’t totally surprise me. I can imagine that it conceivably could make the Chimney Hollow investment (over half a billion dollars) worthless. We’ll see.

I also wonder what Northern plans to do with the contaminated water in the reservoir used to “leach” uranium from the surrounding rock. This is of some concern, since the ultimate plan apparently is to integrate Chimney Hollow water with the rest of Northern’s supply, which we end up drinking. The Federal standard for uranium in drinking water is a maximum of 30 parts per billion, as is Colorado’s. Interestingly, Canada’s (and California’s) standard is 20 parts per billion. What if the leaching doesn’t completely solve the problem?

Northern also faces other financial issues, e.g. with their Northern Integrated Supply Project on the Poudre River. Its costs have jumped from $2 billion to $2.69 billion, causing the Fort Collins-Loveland Water District, about 20% of the project, to abandon participation. The project is now on hold.

Even if the uranium turns out not to be a long-term problem, we are still faced with the continual drying of the West and the increasing shrinkage of the Colorado River as a water source. This may make the whole issue irrelevant, given Windy Gap’s junior water rights position. And it ought to incentivize our city council to take much more seriously the water needs of the excessive development being considered in the current Boulder Valley Comprehensive Plan update.