1. Civil and Environmental Engineering, University of Massachusetts, Amherst, MA 01003.
2. Corresponding author: Civil and Environmental Engineering, University of Massachusetts, 224 Martson Hall, Box 35205, Amherst, MA 01003-5205. Phone: 413-545-5390; Fax: 413-545-2202; E-mail: long@ecs.umass.edu.
3. Carollo Engineers, Kansas City, MO 64131.
4. Environmental Science and Engineering, McGavran-Greenberg Hall, University of North Carolina, Chapel Hill, NC 27599.