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03/18/2014

Rifle Snowmaking in the Name of Science

Sources: Grand Junction [Colorado] Sentinel (Dennis Webb); ESD (Ken Williams, Dan Hawkes)

This past February (2014), ESD geoscientist and avid skier Ken Williams started a snowmaking enterprise in Rifle, Colorado—but not for skiing purposes.

Snowmaking1His snowmaking was part of research associated with uranium cleanup at Rifle (with possible application to sites worldwide)—part of a DOE effort to measure the level of snowmelt infiltration into soil and groundwater at the site. Rifle is of particular interest because groundwater contamination there is taking longer than other sites to naturally dilute. Under high-oxygen, high-nitrogen conditions, bacteria convert uranium to a dissolved form that should flush away over time. At Rifle, low oxygen, low-nitrogen conditions evidently prevent this process from happening, at least at the speed scientists would hope, and they wonder what can be done about it.

Williams and other scientists believe that the vast bulk of infiltration at Rifle and similar sites is tied to snowmelt when evapotranspiration is at a minimum. Their experiment was designed to better understand that process by tracking the migration of meltwater via sample collection up tubes attached to porous cups installed at varying depths underground.

But scientists couldn’t rely on natural snowfall at the site. They needed snow with a distinctive isotopic signature to be able to track its infiltration. Their 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 was quite familiar with as a skier. On ski slopes, snowmakers have access to hydrant and electrical connections. The Rifle site has no water, so Williams arranged for tanks of water to be brought in, as well as a generator.

Snowmaking3Normally the coldest temperatures (when there is little cloud cover) are just before dawn. So, early one morning this past February, scientists planned to start the snowmaking process. As luck would have it, however, the air and ground temperature that morning was too warm to form snow that day, so they waited to the next day to start the process—after alerting police to what they were up to.

Working with a snowmaking team from Aspen Skiing Company (Williams, a season pass holder there, jokingly said he was “calling in a favor”), the group laid down snow from 4 to 10 inches deep over an 800-1000 ft2 area, making a top layer of snow from municipal water to provide a protective cover over the deuterium-marked layer.

Snowmaking2Williams hopes that the study will 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 in late spring and summer versus snow in winter and early spring, for example, could reduce that infiltration—and reduce the dissolution of uranium.

Watch a video of the snowmaking:

Video Replay

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