1. U.S. Geological Survey, Peachtree Business Center, 3039 Amwiler Road, Atlanta, Georgia 30360
2. Centre Saint-Laurent, Environment Canada, Montreal, Quebec H2Y 2E7, Canada
3. U.S. Geological Survey, Branch of Analytical Services, 5293 Ward Road, Arvada, Colorado 80002
4. Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada
5. U.S. Geological Survey, 3535 South Sherwood Forest Boulevard, Suite 120, Baton Rouge, Louisiana 70816