1. Professor and Berger Chair, Civil and Environmental Engineering Dept., Tufts Univ., Medford, MA 02155 (corresponding author).
2. Environmental Engineer, Montana Dept. of Environmental Quality, 1520 E. 6th Ave., Helena, MT 59620.
3. Principal Scientist, National Institute for Water and Atmospheric Research, Gate 10 Silverdale Rd., Hillcrest, Hamilton, NZ 3216.