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January 19, 2017

A regional assessment of untreated groundwater in the Basin and Range basin-fill aquifers, which include parts of Nevada, California, Arizona, Utah and adjacent states, is now available from the U.S. Geological Survey.

The combined Basin and Range basin-fill aquifers rank fourth in the nation as a source of groundwater for public supply, providing about one billion gallons per day for this use. Urban areas within the boundaries of the aquifers include Salt Lake City, Reno, Las Vegas and Phoenix.

Scientists tested for a broad range of water-quality characteristics of untreated groundwater in 78 public-supply wells in the Basin and Range basin-fill aquifers. Results show inorganic constituents present at high concentrations, meaning at levels exceeding human health-benchmarks, in about 20 percent of the study area. Human-made organic constituents (both pesticides and volatile organic compounds) were not detected at high concentrations. The study area includes water at the depth used for public supply. The study evaluated untreated drinking water, but compared results to drinking-water quality standards. The full report is available online.

Many inorganic constituents occur naturally in groundwater. The inorganic constituents found at high concentrations in this study area include arsenic, fluoride, manganese, molybdenum and uranium. Total dissolved solids, a measure of the amount of salt in groundwater, was also found at high levels in 32 percent of the study area. Concentrations of inorganic constituents can be affected by natural processes as well as by human activities. Results also show one or more inorganic constituents present at moderate concentrations (between half the human-health benchmark and the benchmark concentration) in about 49 percent of the aquifer system.

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 source (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 location and summary of water-quality results for five principal aquifers currently available.
Map showing location and summary of water-quality results for five principal aquifers currently available. For more details, please refer to the linked resources in this story.

Between 2013 and 2022, 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. In the future, USGS-led national- and regional-scale modeling will provide a three-dimensional perspective of the quality of the nation’s groundwater that can be used to inform management decisions. More information on USGS regional aquifer assessments can be found in this recent 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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