To help find information outside of your normal discipline:
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Surveillance Epidemiology and End Results
Epidemiology database, includes information on health effects by race, gender, age, etc.

National Health and Nutrition Examination Study
A snapshot of the health of the US population with chemical biomonitoring data for 150+ chemicals

National Cancer Institute 
State by state data for cancer rates

Toxic Release Inventory 
Chemical releases into waterways as a national permitting process

National Pollutant Discharge Elimination System
Information on water point sources