Snowmaking in Rifle in the name of science

An Aspen Skiing Co. snowmaking machine was used recently to deposit snow as part of a research project to measure infiltration of snowmelt into groundwater at a former uranium mill tailings site in Rifle.

A splotch of snow is surrounded by bare ground at a former uranium mill tailings site in Rifle. An Aspen Skiing Co. snowmaking machine was used to deposit the snow as part of a research project to measure infiltration of snowmelt into groundwater there.

A small, flat piece of ground on a former uranium mill tailings site on the eastern edge of Rifle wouldn’t necessarily be the first place you’d think of going skiing.

So it would be only natural to wonder what a tear-drop-shaped patch of snow recently was doing there, and why a snowmaking machine was used to deposit it there in the predawn hours of Feb. 21.

Kenneth Williams, a geological scientist with Lawrence Berkeley National Laboratory, is the guy to ask for answers to these questions, as someone who is leading research there with implications for uranium cleanup at other similar sites in Colorado and nearby states and around the world.

But when it comes to wanting snow laid down at the site, Williams — an Aspen Skiing Co. season pass holder — knew just who to call.

“We don’t understand the science on this end but we do know how to make snow,” said Doug Mackenzie, a special projects manager at the resort who was involved in the Rifle project.

The snow project is designed to measure the level of snowmelt infiltration into soil and groundwater at the site. Williams and other scientists have been doing research at the site with the support of Department of Energy funding. It’s prompted by the fact that groundwater contamination at the site and others like it is taking longer than expected to be naturally diluted to acceptable levels, prompting scientists to investigate why, and if anything can be done about it.

Research in Rifle has involved things such as injecting vinegar into groundwater to foster microbial activity that converts uranium and vanadium into ores to remove them from the groundwater.

That happens in low-oxygen, low-nitrogen conditions. The snow study relates to the fact that in high-oxygen, high-nitrogen conditions, other organisms convert uranium to a dissolved form that should flush away, eventually reaching the nearby Colorado River in a highly diluted quantity as originally had been hoped.

A good way for oxygen and nutrients to be delivered to these organisms and encourage the dissolution process is through infiltration of precipitation through soil to groundwater. But scientists believe little infiltration occurs from rain in warmer months due to moisture evaporation in the heat and transpiration from plants.

Williams says they feel pretty confident that the vast bulk of infiltration at Rifle and similar sites is tied to snowmelt. The current experiment is designed to better understand that process through following the migration of meltwater by pulling samples up tubes attached to porous cups installed at varying depths underground.

But scientists couldn’t just rely on natural snowfall on the site. They needed snow with a distinctive signature to be able to track its infiltration. The scientists’ solution was to make use of water that contains deuterium, a stable isotope marker — and to turn that water into snow in a way Williams is quite familiar with as a skier.

“It was very interesting — very interesting,” Mackenzie said about the project.

On the ski slopes, snowmakers have access to hydrants and electrical connections. The Rifle site has no water, so Williams arranged for tanks to be brought in. The team also rented a generator.

They were set up to go at 5 p.m. Feb. 20, but the air was warm enough the snow would have been wet, the ground was warm enough it probably would have immediately started melting, and it was windy to boot, Mackenzie said.

Normally the coldest temperatures when there is little cloud cover are just before dawn, so the group ended up making snow starting around 4:30 a.m. the following morning, after alerting law enforcement so they wouldn’t wonder about suspicious activity at the site.

The team laid down snow anywhere from about 4 to 10 inches deep, with the top layer created from municipal water to provide a protective cover over the deuterium-marked layer.

The snowmaking team normally works at Snowmass, where snowmaking usually wraps up each winter around the end of December.

“The guys, they were all for loading up and going down (to Rifle) and doing something a little different and seeing how it went. It went off without a hitch,” Mackenzie said.

Williams said Aspen Skiing Co. was generous in volunteering to pick up some of the costs of the operation.

“I don’t know if it helps that I’m a season pass holder here,” he joked. “I called in a favor.”

In return, he’s agreed to give a presentation to the snowmakers about what the study finds.

Said Mackenzie, “I think it will be very interesting, especially for people who make snow all the time, (to learn) what happens when it melts, how it seeps in the ground, at what rate and so forth.”

Williams said the study could shed light on how climate-induced changes in hydrology might affect such cleanup sites. If the sites rely primarily on snowmelt for infiltration, a shift toward more rain versus snow, for example, could reduce that infiltration and the dissolution of uranium.

Something also being studied is the water table at the Rifle site, which also affects microbial activity and uranium behavior. That water table rises dramatically during spring runoff on the Colorado River, another factor that could be affected by climate change.

Researchers hope to apply lessons from the Rifle experiments to similar cleanup efforts in places such as Durango; Gunnison; Moab, Utah; and Shiprock, N.M.

As for the snow experiment, Williams said the snow has all melted, over a period consistent with typical spring snows at the site, nicely mimicking what researchers were trying to simulate. Next comes collecting and evaluating the underground samples.

If Williams needs a break from the project, he always can head back up to Aspen, where there’s lots of snow that has yet to begin to melt and he can enjoy his ski pass.

“I guess he takes pretty good advantage of it,” Mackenzie said.


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