Harold W. Bentley, Stanley N. Davis, University of Arizona

Fred M. Phillips, New Mexico Institute of Mining and Technology

M.A. Habermehl, Bureau of Mineral Resources, Geology & Geophysics Canberra, Australia

Peter L. Airey, Graeme E. Calf, Lucas Heights Research Laboratories, Sutherland, New South Wales

David Elmore, Harry E. Gove, University of Rochester

Thomas Torgersen, Australian National University, Canberra, Australia

Water Resources Research 22 (1986) 1991-2001

Chlorine 36 has many advantages as a dating tool for very old groundwater. These advantages include a suitable half-life (3.01 x 10⁵years), simple geochemistry, conservative behavior in groundwater, and a general absence of subsurface sources of levels comparable to the atmosphere input. Recent advances in tandem accelerator mass spectrometry have permitted the analysis of ³⁶Cl at the low abundance expected following residence in the subsurface for 10⁶ years or more. In order to test the suitability of ³⁶Cl for dating very old groundwater, the ³⁶Cl/Cl ratios of 26 groundwater samples from the Great Artesian Basin of Australia have been measured. Groundwater ages calculated from the ³⁶Cl data compare favorably with ages computed independently from hydrodynamic simulations.