Water Sampling (IMAGE) University of California - Santa Cruz Caption The research team tracked methane concentrations along with radon and radium, naturally occurring elements that serve as tracers for groundwater. Credit Adina Paytan Usage Restrictions For use only with news coverage of this research. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.