1. United States Geological Survey, Columbia, South Carolina 29210, United States
2. United States Geological Survey, Iowa City, Iowa 52240, United States
3. United States Geological Survey, Lawrenceville, New Jersey 08648, United States
4. United States Geological Survey, Reston, Virginia 20192, United States
5. Colorado School of Mines, Golden, Colorado 80401, United States
6. United States Environmental Protection Agency, Durham, North Carolina 27709, United States
7. United States Geological Survey, Portland, Oregon 97201, United States
8. United States Geological Survey, Middleton, Wisconsin 53562, United States
9. United States Geological Survey, Lawrence, Kansas 66049, United States
10. United States Geological Survey, Lakewood, Colorado 80225, United States
11. United States Geological Survey, Lansing, Michigan 48911, United States
12. United States Geological Survey, St. Petersburg, Florida 33701, United States
13. United States Geological Survey, Sacramento, California 95819, United States
14. United States Geological Survey, Kearneysville, West Virginia 25430, United States
15. United States Geological Survey, Oklahoma City, Oklahoma 73159, United States
16. United States National Institute of Environmental Health Sciences/NIH, Bethesda, Maryland 20892, United States