1. Department of Civil, Environmental, and Architectural Engineering, Campus Box 428, University of Colorado, Boulder, Colorado 80309-0428, Department of Chemical Engineering, Environmental Engineering Program, Yale University, New Haven, Connecticut 06520, U.S. Geological Survey, Water Resources Division, 3215 Marine Street, Boulder, Colorado 80303-1066, and Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, Indiana 46556