A new technology that acts like a giant underground filter is successfully beginning to clean up the uranium contaminating an aquifer in a remote Utah canyon. Uranium contamination in groundwater is a serious problem because the toxic metal can travel long distances in underground aquifers, which are vital sources of fresh water for people, animals and agriculture. Recent research at SSRL showed that the filters-called PRBs (permeable reactive barrier) do intercept uranium, but in an unexpected way that has important implications for monitoring, costs, and future technology selection. Scientists expected that uranium would react with a mineral called apatite in the filter to form an inert mineral that would encapsulate uranium, effectively removing it from the water and abating the threat to downstream inhabitants. This general concept had been shown to work well for lead and cadmium-contaminated soils.

Scientists from the US Geological Survey and SSRL recently used synchrotron-based techniques to study this problem and found that uranium adsorbs to the surfaces of the apatite, instead of chemically reacting with it to form a new mineral. The research team-Christopher Fuller and James Davis of the USGS and John Bargar of SSRL - studied samples created in a lab and samples from Fry Canyon, Utah. Several government agencies (USGS, EPA, DOE and BLM) are collaborating at Fry Canyon to demonstrate PRB technology in an aquifer contaminated by an abandoned uranium-ore processing plant. "We knew that the barriers worked to stop uranium, now we know how they work, and we can use this information to predict how long they will work and what the costs will be. This information is necessary to compare this concept to other technologies and to select new designs," Bargar said. This fundamental knowledge will affect the engineering design of all future PRB technologies, and serves as the latest example that many environmental cleanup ideas work differently in reality than in theory. One key area to investigate now is how long the barriers can trap uranium before it gets re-released under certain conditions (e.g., a decrease in groundwater pH or saturation of the uranium binding capacity of the barrier).

To learn more about this research see the full scientific highlight at:
http://www-ssrl.slac.stanford.edu/research/highlights_archive/u_ha_prb.html