1. Soil and Land Systems, School of Earth and Environmental Sciences, Univ. of Adelaide; Waite Campus Glen Osmond SA 5064 Australia
2. CSIRO Land and Water; PMB 2 Glen Osmond SA 5064 Australia
3. National Risk Management Research Lab.; U.S. Environmental Protection Agency; 5995 Center Hill Ave. Cincinnati OH 45224
4. GSECARS, Univ. of Chicago; Chicago IL 60637