The Piedmont and Blue Ridge crystalline-rock aquifers, together with the other rock types in the Piedmont and Blue Ridge regions, rank second in the nation as a source of groundwater for private domestic supply, providing about 360 million gallons per day for this use. The aquifer underlies an area with a population of more than 25 million. Urban areas within the boundaries of the aquifers include Atlanta, Georgia; Charlotte, North Carolina; and suburbs of Richmond, Virginia; Washington, D.C.; Baltimore, Maryland; and Philadelphia, Pennsylvania.

Scientists tested for hundreds of water-quality constituents and characteristics in samples of untreated groundwater from 60 public-supply wells throughout the aquifer. Results were compared to human-health benchmarks.

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Results show one or more inorganic constituents were present at high concentrations, meaning at levels exceeding human health-benchmarks, in groundwater in about 33 percent of the study area. Manmade organic constituents, including pesticides and volatile organic compounds, were not detected in groundwater at high concentrations.

Many inorganic constituents, including trace elements and radioactive constituents, occur naturally in groundwater, although concentrations can be affected by human activities. Radioactive constituents, including radon and gross-alpha activity, were present at high levels in groundwater in about 30 percent of the study area. Most of the radioactivity in groundwater comes from the decay of isotopes of uranium and thorium that are naturally present in minerals found in aquifers. Other inorganic constituents, notably manganese, were detected at high levels in groundwater in about 5 percent of the study area.

“Nuisance” constituents—those that can affect water’s taste, color or odor—were present at high levels, meaning they exceeded the Environmental Protection Agency’s non-mandatory benchmarks, in groundwater in about half of the study area, mostly because of water with low pH. Total dissolved solids, a measure of the salinity of groundwater, was measured at high levels in groundwater in 3 percent of the study area.

Groundwater provides nearly 50 percent of the nation’s drinking water. To help protect this vital resource, the USGS National Water-Quality Assessment, or NAWQA, Project of the National Water Quality Program assesses groundwater quality in aquifers that are important sources of drinking water.

Over the last two decades, USGS scientists have assessed water quality in untreated water from 6,600 wells in extensive regional aquifers that supply most of the groundwater pumped for the nation’s drinking water, irrigation and other uses. This comprehensive sampling, along with detailed information on geology, hydrology, geochemistry and chemical and water use, can be used to explain how and why aquifer vulnerability to contamination varies across the nation.

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Between 2013 and 2023, NAWQA will continue to assess the quality of the nation’s groundwater by sampling about 2,300 shallow wells and 1,400 deep public-supply wells for a broad range of water-quality constituents. USGS-led national- and regional-scale modeling will provide a three-dimensional perspective of the quality of the nation’s groundwater. In conjunction, the data and modeling that can be used to inform management decisions. More information on USGS regional aquifer assessments can be found in this a previous USGS Featured Story. 

To learn more, visit these websites:
USGS National Summary Circular, Quality of the Nation's Groundwater Quality, 1991-2010
Regional reports on principal aquifers of the U.S.
National Water-Quality Assessment (NAWQA) Project
USGS Groundwater Information
WaterSMART