US geochemists have developed a technique for identifying sources of groundwater contamination.

Christopher Brown and colleagues at Pacific Northwest National Laboratory in Washington analysed ruthenium in the groundwater under a storage facility for high-level nuclear waste, the US Department of Energy's Hanford site. The results were used to identify when contamination occurred, which is important at the site, according to Brown. 'Differentiating between purposeful discharges and tank leaks is critical,' he explained.

The technique uses dynamic reaction cell inductively coupled plasma mass spectrometry to analyse ruthenium isotopic ratios in the groundwater.  Brown said that the method is 'a simple and cost effective approach to measure ruthenium isotopic ratios in all but the most dilute aqueous samples.' The ratios can then be used to work out when the waste was generated.

Brown said the team were prompted by the discovery of a significant amount of technetium contamination in the groundwater under the storage facility. Technetium has a long half-life (over two thousand years) and will persist in the environment for a very long time. Technetium and ruthenium are both produced as fission products in nuclear reactors, Brown explained, but technetium, only produced as a single isotope, cannot be used to determine when the waste causing the contamination was generated.  However, ruthenium fission product isotopes have a similar mobility to technetium, are sensitive to reactor conditions and can be used to find when the leak occurred, he said.  

The team hope to expand their technique to look at other fission product isotopes. 'Using a multi-element isotopic approach, we might be able generate a groundwater flow model for the Hanford Site,' suggested Brown.

Stefaan Van Winckel of the Institute for Transuranium Elements in Karlsruhe, Germany, said the work was excellent, offering 'convincing and very useful results-touching such different fields as nuclear, analytical and geochemistry'.  

Katherine Davies