The USGS said it took a close look at ways in which contaminants could make their way into wells used to provide drinking water to the public. It found in a 130-page report the characteristics of some aquifers enable contaminants to stay in or travel to groundwater more readily than others.
"Common sense might say that wells located near known contaminant sources would be the most vulnerable, but this study found that even where contaminant sources are similar, there are differences in public-supply-well vulnerability to contamination," Sandra Eberts, a lead USGS researcher, said in a statement Monday.
USGS said it's difficult to determine which areas are more prone to contamination than others because of varying geological characteristics. USGS researchers looked at groundwater sites from California to Ohio. It said human influences like irrigation can impact aquifer conditions and some of the contaminants, like arsenic, were naturally occurring.
The oil and natural gas drilling practice of hydraulic fracturing, or fracking, has raised concerns about groundwater contamination. Critics say some of the chemicals used in the process could contaminate water supplies. The USGS study did not look directly at fracking.