HR: 1340h
AN: H53A-1195    [Abstracts]
TI: The Impact of Mass Transfer on the H-3/He-3 Dating Method
AU: * Neumann, R B
EM: rneumann@mit.edu
AF: Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 77 Massachusetts Ave., Cambridge, MA 02139 United States
AU: Harvey, C F
EM: charvey@mit.edu
AF: Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 77 Massachusetts Ave., Cambridge, MA 02139 United States
AB: Estimates of groundwater age allow researchers to resolve surface water recharge rates, ascertain an aquifer's susceptibility to contamination, and calibrate complex flow models. The H-3/He-3 groundwater dating method is unique because it does not require exact knowledge of the timing, location, and concentration of an aquifer's highly transient tritium input. In this investigation the impact of mobile-immobile domain mass transfer on the H-3/He-3 dating method is assessed in order to improve age interpretation and bound uncertainty. A finite difference model was constructed to simulate the decay of tritium, production of helium, and the transport of both species through aquifers with a range of parameters. Resulting concentrations were used to calculate H-3/He-3 ages which were compared to corresponding average water ages (the expected value of the water age distribution) and mobile water ages (the age associated with the mobile water velocity). Findings show that the H-3/He-3 method does provide a reasonable approximation of the average water age for heterogeneous, porous aquifers, but that H-3/He-3 measurements must be carefully interpreted for fractured aquifers. Interestingly, the different diffusion coefficients for tritium and helium, suspected to cause inaccuracies in the H-3/He-3 method, have a minimal impact on the H-3/He-3 age.
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting