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December 7, 2017

A regional assessment of untreated groundwater in the Glacial aquifer system, which includes parts of 25 states across the northern contiguous United States, is now available from the U.S. Geological Survey.

The Glacial aquifer system ranks first in the nation as a source of groundwater for public and domestic supply, providing 2.6 billion gallons per day for this use. The aquifer underlies an area with about 98 million people, nearly one third of the country’s population.

Scientists tested for hundreds of water-quality constituents and characteristics in samples of untreated groundwater from 90 public-supply wells throughout the aquifer. Results were compared to human-health benchmarks.

Constituent concentration pie chart for the Glacial Aquifer System

Water from 74 percent of the study area did not have a high concentration of any constituent with a human-health benchmark. Results show one or more inorganic constituents were measured in groundwater at high concentrations, meaning at levels exceeding human-health benchmarks, in about 26 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 nutrients, occur naturally in groundwater, although concentrations can be affected by human activities. The trace elements manganese, arsenic and strontium were detected at high levels in groundwater in about 24 percent of the study area. The nutrient nitrate, which has both natural and human-related sources, was detected at high concentrations in groundwater in about 1 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 65 percent of the study area. Total dissolved solids, a measure of the salinity of groundwater, occurred at high concentrations in groundwater in 28 percent of the study area.

Groundwater provides nearly half 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.

Map showing summary of groundwater-quality results

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 can be used to inform management decisions. More information on USGS regional aquifer assessments can be found in this 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

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