![[logo] US EPA](http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}
Research Highlights
Breaking the Age Barrier: New Research in Ground Water Quality
Most people are familiar with the use of radiocarbon dating to place once-living objects in their historical period. In a parallel approach, NRMRL hydrologists are pioneering the measurement of naturally occurring radioactive isotopes to determine the age (that is, the residence time) of ground water in support of watershed contamination studies. While age-dating of young ground water (ground water that's less than 50 years old) is a frontier field in watershed studies, it has long been realized that very young ground water could be a more significant source of contamination than older water. This is true because a shorter residence time means that ground water moves "faster." Thus, contamination will get to the drinking well from the recharge area (point of entry) faster if the ground water is younger. However, it has been difficult to measure the exact age of young ground water. The conventional indicator has been tritium, a radioactive form of hydrogen, but its usefulness has nearly ended because of a short half-life combined with its last significant input to the atmosphere from thermonuclear tests of the early 1950s. NRMRL isotope hydrologists believe that dissolved krypton gas (in the isotope form of 85Kr) may be the best indicator, among the other potentially useful isotopes tested, of young recharge water. 85Kr is ideal for several reasons:
Apparent ages of water 20m below local water table, Royal River Watershed, Maine, 2004 Furthermore, because it is chemically inert, it retains its unique isotope characteristics while it decays as predictably as the unwinding of a clock. Until recently, the chief shortcoming of this method was the daunting task of collecting voluminous water samples to measure traces of the rare 85Kr isotope. Finally, a breakthrough in field collection and laboratory measurement has permitted the new 85Kr isotope method to detect ground water as young as 2 years and as old as 50 years. For the first time, the widespread economical use of the new 85Kr method has been applied to selected watersheds where elevated natural occurrences of arsenic and lead have prompted hydrologists to ask whether, and how, the ground water will flush these materials out over time. Recent research in Maine, for example, suggests that a vulnerability map can be plotted using the new 85Kr technique, either alone or through integration with conventional hydrology investigations. In cooperation with the State of Maine and rural ground water supply districts, NRMRL researchers are using this innovative approach to help diagnose prospective contamination areas so that water supply managers can effectively plan well fields to ensure a stable supply of clean drinking water. Detailed information is available in: Sidle, W.C. 2006. "Apparent 85Kr Ages of Ground Water Within the Royal Watershed, Maine, USA." Journal of Environmental Radioactivity. 91:113–127. ContactFor further information, please contact Jane Ice, NRMRL Public Information Office, 513-569-7311. New NRMRL PublicationsBook ChapterImpellitteri, Christopher A. and Herbert E. Allan. 2007. "Effects of Humic Substances on Attenuation of Metals Bioavailability and Mobility in Soils." In Natural Attenuation of Trace Element Availability in Soils. R. Hamon, M. McLaughlin, and E. Lombi (eds.). SETAC Press, Pensacola, FL. EPA ReportsU.S. EPA. 2006. Southern Research Institute Evaluation and Mitigation of Visible Acidic Aerosol Plumes from Coal-Fired Power Boilers (PDF). (103 pp, 1.7 MB) (EPA/600/R-06/156) U.S. EPA. 2007. Speciate 4.0: Speciation Database Development Documentation—Final Report. (EPA/600/R-06/161) – Abstract |
