1. US EPA, Office of Research and Development, Center for Public Health and Environmental Assessment, Research Triangle Park, North Carolina 27709, United States
2. Abt Associates, Division of Health and Environment, Boulder, Colorado 80302, United States
3. US EPA, Office of Water, Office of Ground Water and Drinking Water, Washington, District of Columbia 20460, United States
4. US EPA, Office of Research and Development, Center for Environmental Solutions and Emergency Response, Cincinnati, Ohio 45268, United States
5. US EPA, Office of Research and Development, Center for Public Health and Environmental Assessment, Boston, Massachusetts 02109, United States