1. Research Assistant Professor, Dept. of Biological Systems Engineering, Seitz Hall, Virginia Tech, Blacksburg, VA 24060 (corresponding author).
2. Assistant Engineer, Hazen and Sawyer, Raleigh, NC 27607.
3. Associate Professor, Dept. of Environmental Sciences and Engineering, Gillings School of Global Public Health, Univ. of North Carolina, Rosenau Hall—CB7431, Chapel Hill, NC 27599-7431.
4. Professor, Dept. of Environmental Sciences and Engineering, Gillings School of Global Public Health, Univ. of North Carolina, Rosenau Hall—CB7431, Chapel Hill, NC 27599-7431.