Groundwater Quality in Principal Aquifers of the Nation, 1991–2010

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What’s in your groundwater? Learn about groundwater quality in the Principal Aquifers of nine regions across the United States in informative circulars filled with figures, photos, and water-quality information.

Groundwater is our invisible, vital resource—more than 75 billion gallons are pumped each day, and 155 million people rely on groundwater for drinking water. Although groundwater is a safe, reliable source of drinking water for millions of people nationwide, high concentrations of some chemical constituents can pose potential human-health concerns. Some of these contaminants come from the rocks and sediments of the aquifers themselves, and others are chemicals that we use in agriculture, industry, and day-to-day life.

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.

Based on thousands of samples collected from 1991 to 2010, the National Water-Quality Assessment Project has created informative circulars on water quality and the factors that affect it for each of nine regions, comprising 20 Principal Aquifers—regionally extensive aquifers that supply groundwater for drinking, irrigation, and other uses. The results for the Nation are summarized in a single circular. Samples were collected from 6,600 public-supply, domestic (private), and monitoring wells, and analyzed for a wide range of contaminants and constituents, including pesticides, nutrients, and radionuclides. Explanations of the findings presented in these circulars improve our understanding of the natural and human factors that affect the occurrence of contaminants in the Nation’s groundwater.

Learn more about USGS research on groundwater.

Regional Assessments of Principal Aquifers

Regional Assessments of Principal Aquifers

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.

Click on the "Related Science" tab to find out more about our Nation's groundwater quality.