Why are some wells contaminated and some are not?

All wells are not equally vulnerable to contamination because of differences in three factors: the general aquifer chemistry, groundwater age, and paths within aquifer systems that allow water and contaminants to reach a well.

More than 100 million people in the United States receive their drinking water from public groundwater systems, which can be vulnerable to naturally occurring contaminants such as radon, uranium, arsenic, and man made compounds, including fertilizers, septic-tank leachate, solvents and gasoline hydrocarbons.