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December 7, 2017

A regional assessment of untreated groundwater in the Rio Grande aquifer system, which includes parts of Colorado, New Mexico and Texas, is now available from the U.S. Geological Survey.

The Rio Grande aquifer system ranks 18th in the nation as a source of groundwater for public supply, providing 240 million gallons per day for this use. Urban areas within the boundaries of the aquifers include Albuquerque, New Mexico, and El Paso, Texas.

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. At least one constituent was measured at a high concentration, meaning it exceeded its human-health benchmark, in groundwater in 30 percent of the study area.

Constituent concentration pie chart for the Rio Grande Aquifer System

The trace element arsenic was the inorganic constituent most frequently detected in groundwater at high concentrations, and exceeded the human-health benchmark in 18 percent of the study area. Trace elements fluoride, strontium and uranium were measured in groundwater at high levels in 3 percent of the study area. Radioactive constituents, including gross-alpha activity and radon, were present at high levels in groundwater in about 5 percent of the study area. Most of the radioactivity in groundwater comes from the decay of isotopes of uranium and thorium that are present in minerals found in aquifers.

Many inorganic constituents, including trace elements and radioactive constituents, occur naturally in groundwater, although concentrations can be affected by human activities. The nutrient nitrate, which has natural and human-related sources, was detected at high concentrations in about 2 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 about 10 percent of the study area. Total dissolved solids, a measure of the salinity of groundwater, was also measured at high concentrations in groundwater in 35 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.

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


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