1. B. M. Kennedy, Center for Isotope Geochemistry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
2. Y. K. Kharaka, W. C. Evans, J. Thordsen, G. Ambats, R. H. Mariner, Water Resources Division, U.S. Geological Survey, Menlo Park, CA 94025, USA.
3. A. Ellwood and D. J. DePaolo, Center for Isotope Geochemistry, Geology and Geophysics Department, University of California, and Lawrence Berkeley National Laboratory, Berkeley, CA 94720–4767, USA.