Krypton Isotope Hydrology

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0409756SturchioThe age of groundwater is one of the most elusive geologic parameters to quantify, despite itscrucial significance for water resources, waste management, subsurface reactive transport, andpaleoclimate studies. It has long been recognized that 81 Kr is a nearly ideal tracer fordetermining residence times of old groundwater in the 5 10 4 10 6 year range, yet because of itslow abundance ( 81 Kr/Kr 10 -12 ) it has been nearly impossible to measure. However, a newtechnique for measurement of 81 Kr/Kr ratios in small quantities of Kr (as little as 50 micromoles)was recently reported (Atom-Trap Trace Analysis, or ATTA; Chen et al., 1999; Du et al., 2003),and its application to old groundwater was demonstrated successfully by the PI and colleagues intheir NSF-funded study of the Nubian Aquifer, Egypt (Sturchio et al., 2003). That studyestablished the feasibility of using the ATTA technique for routine 81 Kr/Kr measurement inhydrologic investigations of systems having long groundwater residence times. The ATTAtechnique, which can also be used for measuring 85 Kr/Kr, is thus an ideal tool with which toaddress a range of fundamental questions in hydrology.This proposal requests support for a graduate student to work with the PI and colleagues(Z. T. Lu's group at Argonne National Laboratory) in developing further applications of the traceKr isotopes ( 81 Kr and 85 Kr) in hydrologic investigations. The intellectal merit of this research isthat it will lead to an enhanced understanding of the water cycle within the Earth's crust.Specific investigations that we propose are: (1) to determine the residence time of salinegroundwaters in the central U.S.A., which on the basis of stable isotope data are believed to havetraveled more than 1,000 km from a recharge area in the Rocky Mountains (Musgrove andBanner, 1993), and which should therefore have a residence time on the order of 10 6 years; (2) toconstrain the residence time of hydrothermal waters at Yellowstone National Park, for whichlittle information is available (Pearson and Truesdell, 1978); (3) to determine the residence timeof groundwater in the Milk River aquifer of southern Alberta, which was the subject of an earliermulti-tracer study sponsored by the IAEA that was focused on dating very old groundwater(Ivanovich, Frohlich, and Hendry, 1991); and to investigate residence times of young (50 yr)groundwaters where other tracers such as tritium-helium and CFC's do not provide coherentresults. These investigations are representative of the broad range of potential applications oftrace Kr isotopes in groundwater hydrology.The broader impact of the proposed research is that it will provide opportunities forresearch, training, and education at the University of Illinois at Chicago (UIC), which has thenation's fifth most diverse student population; it will establish enhanced local Chicago-areapartnership for routine application of trace Kr isotopes in hydrology, because the Kr separationswill henceforth be performed in a laboratory at UIC (rather than in Switzerland as in the previousNSF-funded study) with ATTA measurements performed nearby at Argonne NationalLaboratory; it will help establish the new subdiscipline of Kr isotope hydrology, which may havesignificant impact on hydrologic investigations and water resources management worldwide.