1. Environmental Engineer, Environmental Sciences Div., Argonne National Laboratory, EVS-240, Argonne, IL 60439; formerly, NRC Postdoctoral Associate, U.S. Geological Survey, Reston, VA (corresponding author).
2. Professor, Dept. of Civil Engineering, St. Anthony Falls Laboratory, Univ. of Minnesota-Twin Cities, 2 Third Ave. SE, Minneapolis, MN 55414.
3. Hydrologist, U.S. Geological Survey, Mail Stop 430 National Center, Reston, VA 20192.