Cement prison for old radioactive waste

in the ground, they need to show that they can control and predict microbial calcite formation. That iss easy enough to do in a laboratory beaker, but reining in bacteria and chemical reactions in a complex underground environment has posed many practical and scientific challenges.

For instance, in one of their first field experiments, Fujita and her colleagues generated so much calcite that they clogged their injection well and burned out a pump. “What a success!” Fujita recalls collaborator and University of Idaho geochemist Robert Smith saying upon hearing the news. “He was only half-joking,” Fujita says. The clog made it difficult for the researchers to measure how much calcite they’d made or how much bacterial growth they had stimulated.

For their next set of field experiments, the team upgraded to multiple wells and moved to the Vadose Zone Research Park at the INL desert Site.

Having more than one well meant they could create their own water flow and study how far they could get the injected urea to go. They had trouble, however, getting the urea and molasses injections to go the way they wanted.

Henriksen describes the problem by sketching an underground stream taking a tortuous route through hidden gravel pits and around impermeable layers of basalt and clay before finally draining into the Snake River Plain Aquifer. “It’s really complicated and dynamic,” Henriksen says. “You can’t just reach down there and make the water go where you want.”

In addition, the amount and rates of water moving through the ground at the park can change. Fujita and colleagues spent their first year at the research park studying underground water movement. The team showed up the next year with many carefully planned experiments, only to find that the park water conditions had drastically changed. One well was even completely dry. The experiments had to be scrapped.

Fujita, Smith, and Henriksen have not yet given up on microbial calcite. They took care to locate their latest experiment at a well-studied DOE research site at an old uranium ore processing facility in Rifle, Colorado. Henriksen and his colleagues are evaluating the effect of their molasses and urea injections on the local microbe community and working with hydrologists to help them understand Rifle’s underground water dynamics. The INL researchers couldn’t dig up enough of the ground to look directly at how much calcite they’d generated and where, so they enlisted geophysicists to help them detect those things remotely with ground radar and by measuring any effects the underground reactions might have had on the ground’s capacity to conduct electric current.

The forthcoming results of the Rifle experiment should get INL researchers closer to being able to predict the results of future efforts to stimulate microbial calcite formation. The researchers would like to expand their knowledge of the process with more and larger scale tests at contaminated locations, such as a pilot study at the Washington site, Fujita says.

Despite the frustration of thwarted experiments, Henriksen remains enchanted by the complexity of studying and manipulating microbes in the environment.

“Most people don’t think about the bacteria everywhere around them or about utilizing the amazing capabilities bacteria have,” Henriksen says. “They can do a lot of things we can’t. Now we have the tools to work with them.”

— Read more in Yoshiko Fujita et al., “Evaluating the Potential of Native Ureolytic Microbes To Remediate a 90Sr Contaminated Environment,” Environmental Science & Technology 44, no. 19 (3 September 2010): 7652–58 (DOI: 10.1021/es101752p); and Jeanne Kjær et al., “Leaching of Metribuzin Metabolites and the Associated Contamination of a Sandy Danish Aquifer,” Environmental Science & Technology 39, no. 21 (29 September 2005): 8374–81 (DOI: 10.1021/es0506758)