HR: 1340h
AN: H13G-1669    [Abstracts]
TI: Redox and Recharge Controls on Sub-Surface Radium-Isotope Mobility.
AU: * Todd, V M
EM: vtodd@usc.edu
AF: University of Southern California, Dept. of Earth Sciences, 3651 Trousdale Pkwy. ZHS-117, Los Angeles, CA 90089-0740, United States
AU: Gentry, R W
EM: rgentry@utk.edu
AF: University of Tennessee, Civil and Environmental Engineering, 311 Conference Center Building, Knoxville, TN 37996, United States
AU: Ku, T
EM: rku@usc.edu
AF: University of Southern California, Dept. of Earth Sciences, 3651 Trousdale Pkwy. ZHS-117, Los Angeles, CA 90089-0740, United States
AB: Groundwater geochemical systems are known to be highly complex, driven by a wide variety of physical, chemical and biological mechanisms. A north-south transect of wells in the Sheehan well-field (Memphis, TN) that border an aquitard window were used to sample the confined Memphis Aquifer. Short-lived (²²³Ra and ²²⁴Ra) and long-lived isotopes (²²⁶Ra and ²²⁸Ra) of radium were examined in the colloidal and dissolved groundwater phases to constrain the geochemical mechanisms affecting the Memphis Aquifer. Measured isotope activities increase from the periphery to the center of the measured transect by 0.5 to 1.0 orders of magnitude for all Ra-isotopes. Wells east of the transect show an additional increase of 0.3 orders of magnitude for short-lived Ra-isotopes. Additionally, ²²³Ra/²²⁶Ra and ²²⁴Ra/²²⁶Ra activity- ratios increased as a function of distance from the local aquitard window. The results suggest 1) low Ra-isotope activities close to the aquitard window by association with the solid-phase, and 2) the increase of short-lived over long-lived Ra-isotope activities further away from the aquitard window due to alpha-recoil.
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2007 Fall Meeting