New USGS Reports Describe Groundwater Vulnerability to Contamination

One in every five samples of groundwater used as a source for drinking contains at least one contaminant at a level of concern for human health, according to a new U.S. Geological Survey report.

About 115 million people—more than one-third of the Nation’s population—rely on groundwater for drinking water, and the need for high-quality drinking-water supplies is becoming more urgent as the Nation’s population grows.

USGS scientists assessed water quality in source (untreated) water from 6,600 wells in regionally extensive aquifers that supply most of the groundwater pumped for the Nation’s drinking water, irrigation, and other uses.  The new USGS reports highlight how geology, hydrology, geochemistry, and chemical use affect the concentrations of individual contaminants in groundwater.

When groundwater supplies are contaminated, millions of dollars can be required for treatment so that the supplies can be usable. Contaminants in groundwater can also affect the health of our streams and valuable coastal waters. By knowing where contaminants occur in groundwater, what factors control contaminant concentrations, and what kinds of changes in groundwater quality might be expected in the future, we can ensure the availability and quality of this vital natural resource in the future.

Major Findings

  • Contaminants from geologic or manmade sources were a potential human-health concern in one of every five wells sampled in the parts of aquifers used for drinking water
  • Differences in geology, hydrology, geochemistry, and chemical use explain how and why aquifer vulnerability and concentrations of contaminants vary across the Nation
  • Changes to groundwater flow have also altered groundwater quality
  • Our actions today are determining groundwater quality for decades to come

Regional summaries of where and why groundwater is vulnerable to contamination now are available for the following aquifers and aquifer systems:


Aquifers of the Piedmont, Blue-Ridge and Valley and Ridge Regions (eastern U.S.)

Northern Atlantic Coastal Plain Surficial Aquifer System (east coast of the U.S.)
Glacial Aquifer System (northern U.S.)

Western Volcanics (northwestern U.S. and Hawaii)

Southwest Basin-Fill Aquifers (southwestern U.S.)

Denver Basin Aquifer System (Colorado)

High Plains Aquifer System (central U.S.)

Mississippi Embayment-Texas Coastal Upland Aquifer System and Mississippi River Alluvial Aquifer

Upper Floridan Aquifer and Overlying Surficial Aquifer (southeastern U.S.)

These reports and the associated water quality data are available online.

Additional information on the activities of the USGS National Water -Quality Assessment Program’s groundwater quality for the next decade is available online.

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