Image courtesy of the U.S. Geological Survey
The U.S. Geological Survey compiled more than 230 aquifer studies for a snapshot of groundwater quality in 62 principal aquifers the United States. The map above shows the percentage of wells in each aquifer that had at least one contaminant at a concentration higher than federal standards for human health. Green wedges show naturally occurring sources, while red indicates the share of wells with man-made contaminants.