Groundwater Quality—Current Conditions and Changes Through Time Active
Groundwater—Our Invisible But Vital Resource
Long-Term Changes in Groundwater Quality
Use the interactive online mapper to see how groundwater quality across the Nation has changed over the decades
Rapid Fluctuations in Groundwater Quality—What Do They Mean?
View groundwater quality changes in real time
Is groundwater the source of your drinking water? The USGS is assessing the quality of groundwater used for public supply using newly collected data along with existing water-quality data. Learn more about this invisible, vital resource so many of us depend on.
As part of the National Water Quality Program (NWQP), groundwater quality is being characterized in 20 of the Nation's 68 Principal Aquifers. These 20 aquifers supply most of the groundwater used in the United States—they account for more than three-quarters of the groundwater pumped for public supply and 85 percent of the groundwater pumped for domestic supply.
About 140 million people—almost one-half of the Nation’s population—rely on groundwater for drinking water. Regional assessments of groundwater quality are one component of the NWQP's ongoing efforts to assess, understand, and forecast the quality of the Nation’s groundwater.
Samples collected by the NWQP for the surveys of Principal Aquifers are analyzed for a large suite of regulated and unregulated constituents, including pesticides, radionuclides, metals, and pharmaceuticals. The Principal Aquifer surveys focus on characterizing the quality of groundwater prior to treatment, not the treated drinking water delivered to consumers.
Regional Assessments of Groundwater Quality
To characterize the quality of groundwater many people use for drinking, almost 1,100 deep public-supply wells have been sampled within 15 Principal Aquifers. Although samples are from source water prior to any treatment, for context the results are compared to human-health benchmarks for drinking water.
Groundwater samples were analyzed for hundreds of water-quality constituents. What have we learned?
- At least one inorganic constituent exceeded a human-health benchmark in all of the 15 Principal Aquifers surveyed to date, ranging from 3 to 50 percent of samples.
- At least one organic constituent exceeded a human-health benchmark in 2 of the 15 Principal Aquifers surveyed to date, ranging from 3 to 5 percent of samples.
- Contaminants from geologic sources—primarily trace elements such as arsenic, fluoride, and manganese—most commonly exceeded human-health benchmarks. The Floridan aquifer system was an exception, where strontium was the only trace element to exceed human-health benchmarks.
- At least one radioactive constituent exceeded a human-health benchmark in a small percentage of samples—1 to 10 percent—in most of the 15 Principal Aquifers studied. The exceptions were the Piedmont and Blue Ridge crystalline-rock aquifers and the Cambrian-Ordovician aquifer system, where exceedances were 30 and 45 percent, respectively.
- The nutrient nitrate was the only constituent from manmade sources that exceeded its human-health benchmark, typically in a low percentage of samples (1 or 2 percent). These exceedances occurred in the Floridan aquifer system, the Glacial aquifer system, the Rio Grande aquifer system, and the Valley and Ridge and Piedmont and Blue Ridge carbonate-rock aquifers.
The results are explained in easy-to-understand fact sheets, accessible below:
- The Columbia Plateau basaltic-rock aquifers (northwestern U.S.)
- The High Plains Aquifers (western U.S.)
- The Ozarks Plateaus aquifer system (central U.S.)
- The Biscayne aquifer (southeastern U.S.)
- The Basin and Range basin-fill aquifers (western U.S.)
- The Rio Grande aquifer system (southwestern U.S.)
- The Coastal Lowlands aquifer system (south central U.S.)
- The Mississippi Embayment-Texas Coastal Uplands aquifer system (south-central U.S.)
- The Floridan aquifer system (southeastern U.S.)
- The Southeastern Coastal Plain aquifer system (southeastern U.S.)
- The Northern Atlantic Coastal Plain aquifer system (east coast of U.S.)
- The Piedmont and Blue Ridge crystalline-rock aquifers (eastern U.S)
- The Valley and Ridge carbonate-rock aquifers and the Piedmont and Blue Ridge carbonate-rock aquifers (eastern U.S.)
- The Cambrian-Ordovician aquifer system (north central U.S.)
- The Glacial aquifer system (northern U.S.)
How has groundwater quality changed over the decades?
Groundwater-quality monitoring data collected many regions of the United States have been synthesized into a national assessment of groundwater-quality trends. Between 1991 and 2010, NAWQA completed assessments groundwater-quality in Principal Aquifers across much of the United States. The assessments characterized groundwater in both deep public-supply wells and shallower domestic (private) wells. Many of those wells have been resampled on a near-decadal timeframe to determine if groundwater quality has changed over time. To date 1,718 wells in 73 well networks—20-30 randomly selected wells designed to examine groundwater quality in a region— have been resampled on a near-decadal time period. The National Water Quality Program will continue to resample wells periodically to build on our understanding of long-term trends in groundwater quality.
An interactive web tool maps these decadal changes in groundwater quality. Using the web tool, users can easily visualize changes in both inorganic and organic constituent concentrations in groundwater, including chloride, nitrate, several pesticides, and some drinking-water disinfection byproducts. The website also includes a description of the methods used to evaluate changes in groundwater quality and a link to the complete set of data.
Shorter-term fluctuations in water quality
As part of the USGS National Water Quality Program, scientists are investigating why, in some areas and at some depths, groundwater quality changes at short timescales—years to months to days to hours, rather than decades. These fluctuations often are in areas where groundwater and surface water interact. This study, called the Enhanced Trends Network, is evaluating these rapid fluctuations, identifying what causes them, and determining whether the changes are just part of a seasonal trend or are part of an overall long-term trend. For those chemical constituents with human-health benchmarks (thresholds for drinking-water quality), changes in constituent concentrations are being evaluated in the context of those benchmarks—in other words, are there certain conditions under which the groundwater might require treatment before drinking?
Learn more about how the Enhanced Trends Network is providing insight on short-term fluctuations in groundwater quality.
Featured Study
Scientists home in on causes of high radium levels in key Midwestern aquifer
As part of the Principal Aquifer surveys, scientists were able to shed new light on processes that happen deep underground. These processes—which cause radium to leach from aquifer rocks into groundwater—are responsible for high concentrations of naturally occurring radium in groundwater from the Cambrian-Ordovician aquifer. This aquifer provides more than 630 million gallons of water a day for public supply to parts of Illinois, Iowa, Missouri, Michigan, Minnesota, and Wisconsin.
This USGS study helps explain how radium isotopes 224, 226, and 228 make their way into water in the Cambrian-Ordovician aquifer and where concentrations are highest. The study, part of the USGS National Water Quality Assessment Project, reports that water that was recharged into the aquifer long ago, that contains greater amounts of dissolved minerals, and that is low in dissolved oxygen is more likely to leach radium from the surrounding rock.
The groundwater tested came from public supply wells, before treatment and distribution. Radium can be removed from drinking water through treatment, thereby limiting the health risks it poses. Private wells were not tested during this study, however, more than half a million people get their drinking water from private wells that tap the Cambrian-Ordovician aquifer. These homeowners might consider having their water tested for radium.
Curious to learn more about groundwater quality near you? Learn about groundwater quality in 22 Principal Aquifers in nine regions across the United States in informative circulars filled with figures, photos, and water-quality information.
Visit the web pages below to learn more about groundwater quality across the United States and the factors that affect it.
Groundwater Quality in Principal Aquifers of the Nation, 1991–2010
Access the data releases in this topic here. Explore more data releases on groundwater quality at ScienceBase.
Below, you’ll find the latest in peer-reviewed journal articles and USGS reports on groundwater-quality in the Nation’s principal aquifers. For more publications on groundwater quality, look here or search the USGS Publications Warehouse. Look here for help using the Pubs Warehouse.
Tritium as an indicator of modern, mixed, and premodern groundwater age
Predicting redox conditions in groundwater at a regional scale
The quality of our Nation's waters: groundwater quality in the Columbia Plateau and Snake River Plain basin-fill and basaltic-rock aquifers and the Hawaiian volcanic-rock aquifers, Washington, Idaho, and Hawaii, 1993-2005
The quality of our Nation's waters: water quality in the glacial aquifer system, northern United States, 1993-2009
The quality of our Nation's waters: water quality in the Northern Atlantic Coastal Plain surficial aquifer system, Delaware, Maryland, New Jersey, New York, North Carolina, and Virginia, 1988-2009
The quality of our Nation's waters: Water quality in basin-fill aquifers of the southwestern United States: Arizona, California, Colorado, Nevada, New Mexico, and Utah, 1993-2009
The quality of our nation's waters: water quality in the Principal Aquifers of the Piedmont, Blue Ridge, and Valley and Ridge regions, eastern United States, 1993-2009
The quality of our Nation's waters: water quality in the Upper Floridan aquifer and overlying surficial aquifers, southeastern United States, 1993-2010
The quality of our Nation's waters: water quality in the Mississippi embayment-Texas coastal uplands aquifer system and Mississippi River Valley alluvial aquifer, south-central United States, 1994-2008
Groundwater studies: principal aquifer surveys
Trends in groundwater quality in principal aquifers of the United States, 1988-2012
The quality of our Nation's waters: Water quality in the Denver Basin aquifer system, Colorado, 2003-05
Water Quality in the High Plains Aquifer, Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming, 1999-2004
Below are news stories associated with this project.
Contaminants present in many parts of the Glacial aquifer system
Are you one of 30 million Americans whose drinking-water supply relies on groundwater from the glacial aquifer system? A new USGS study assesses the quality of untreated groundwater from this critical water resource, which underlies parts of 25 northern U.S. states.
- Overview
Is groundwater the source of your drinking water? The USGS is assessing the quality of groundwater used for public supply using newly collected data along with existing water-quality data. Learn more about this invisible, vital resource so many of us depend on.
As part of the National Water Quality Program (NWQP), groundwater quality is being characterized in 20 of the Nation's 68 Principal Aquifers. These 20 aquifers supply most of the groundwater used in the United States—they account for more than three-quarters of the groundwater pumped for public supply and 85 percent of the groundwater pumped for domestic supply.
About 140 million people—almost one-half of the Nation’s population—rely on groundwater for drinking water. Regional assessments of groundwater quality are one component of the NWQP's ongoing efforts to assess, understand, and forecast the quality of the Nation’s groundwater.
Samples collected by the NWQP for the surveys of Principal Aquifers are analyzed for a large suite of regulated and unregulated constituents, including pesticides, radionuclides, metals, and pharmaceuticals. The Principal Aquifer surveys focus on characterizing the quality of groundwater prior to treatment, not the treated drinking water delivered to consumers.
Regional Assessments of Groundwater Quality
To characterize the quality of groundwater many people use for drinking, almost 1,100 deep public-supply wells have been sampled within 15 Principal Aquifers. Although samples are from source water prior to any treatment, for context the results are compared to human-health benchmarks for drinking water.
Groundwater samples were analyzed for hundreds of water-quality constituents. What have we learned?
- At least one inorganic constituent exceeded a human-health benchmark in all of the 15 Principal Aquifers surveyed to date, ranging from 3 to 50 percent of samples.
- At least one organic constituent exceeded a human-health benchmark in 2 of the 15 Principal Aquifers surveyed to date, ranging from 3 to 5 percent of samples.
- Contaminants from geologic sources—primarily trace elements such as arsenic, fluoride, and manganese—most commonly exceeded human-health benchmarks. The Floridan aquifer system was an exception, where strontium was the only trace element to exceed human-health benchmarks.
- At least one radioactive constituent exceeded a human-health benchmark in a small percentage of samples—1 to 10 percent—in most of the 15 Principal Aquifers studied. The exceptions were the Piedmont and Blue Ridge crystalline-rock aquifers and the Cambrian-Ordovician aquifer system, where exceedances were 30 and 45 percent, respectively.
- The nutrient nitrate was the only constituent from manmade sources that exceeded its human-health benchmark, typically in a low percentage of samples (1 or 2 percent). These exceedances occurred in the Floridan aquifer system, the Glacial aquifer system, the Rio Grande aquifer system, and the Valley and Ridge and Piedmont and Blue Ridge carbonate-rock aquifers.
The results are explained in easy-to-understand fact sheets, accessible below:
- The Columbia Plateau basaltic-rock aquifers (northwestern U.S.)
- The High Plains Aquifers (western U.S.)
- The Ozarks Plateaus aquifer system (central U.S.)
- The Biscayne aquifer (southeastern U.S.)
- The Basin and Range basin-fill aquifers (western U.S.)
- The Rio Grande aquifer system (southwestern U.S.)
- The Coastal Lowlands aquifer system (south central U.S.)
- The Mississippi Embayment-Texas Coastal Uplands aquifer system (south-central U.S.)
- The Floridan aquifer system (southeastern U.S.)
- The Southeastern Coastal Plain aquifer system (southeastern U.S.)
- The Northern Atlantic Coastal Plain aquifer system (east coast of U.S.)
- The Piedmont and Blue Ridge crystalline-rock aquifers (eastern U.S)
- The Valley and Ridge carbonate-rock aquifers and the Piedmont and Blue Ridge carbonate-rock aquifers (eastern U.S.)
- The Cambrian-Ordovician aquifer system (north central U.S.)
- The Glacial aquifer system (northern U.S.)
How has groundwater quality changed over the decades?
Groundwater-quality monitoring data collected many regions of the United States have been synthesized into a national assessment of groundwater-quality trends. Between 1991 and 2010, NAWQA completed assessments groundwater-quality in Principal Aquifers across much of the United States. The assessments characterized groundwater in both deep public-supply wells and shallower domestic (private) wells. Many of those wells have been resampled on a near-decadal timeframe to determine if groundwater quality has changed over time. To date 1,718 wells in 73 well networks—20-30 randomly selected wells designed to examine groundwater quality in a region— have been resampled on a near-decadal time period. The National Water Quality Program will continue to resample wells periodically to build on our understanding of long-term trends in groundwater quality.
An interactive web tool maps these decadal changes in groundwater quality. Using the web tool, users can easily visualize changes in both inorganic and organic constituent concentrations in groundwater, including chloride, nitrate, several pesticides, and some drinking-water disinfection byproducts. The website also includes a description of the methods used to evaluate changes in groundwater quality and a link to the complete set of data.
Shorter-term fluctuations in water quality
As part of the USGS National Water Quality Program, scientists are investigating why, in some areas and at some depths, groundwater quality changes at short timescales—years to months to days to hours, rather than decades. These fluctuations often are in areas where groundwater and surface water interact. This study, called the Enhanced Trends Network, is evaluating these rapid fluctuations, identifying what causes them, and determining whether the changes are just part of a seasonal trend or are part of an overall long-term trend. For those chemical constituents with human-health benchmarks (thresholds for drinking-water quality), changes in constituent concentrations are being evaluated in the context of those benchmarks—in other words, are there certain conditions under which the groundwater might require treatment before drinking?
Learn more about how the Enhanced Trends Network is providing insight on short-term fluctuations in groundwater quality.Featured Study
Scientists home in on causes of high radium levels in key Midwestern aquifer
As part of the Principal Aquifer surveys, scientists were able to shed new light on processes that happen deep underground. These processes—which cause radium to leach from aquifer rocks into groundwater—are responsible for high concentrations of naturally occurring radium in groundwater from the Cambrian-Ordovician aquifer. This aquifer provides more than 630 million gallons of water a day for public supply to parts of Illinois, Iowa, Missouri, Michigan, Minnesota, and Wisconsin.
This USGS study helps explain how radium isotopes 224, 226, and 228 make their way into water in the Cambrian-Ordovician aquifer and where concentrations are highest. The study, part of the USGS National Water Quality Assessment Project, reports that water that was recharged into the aquifer long ago, that contains greater amounts of dissolved minerals, and that is low in dissolved oxygen is more likely to leach radium from the surrounding rock.
The groundwater tested came from public supply wells, before treatment and distribution. Radium can be removed from drinking water through treatment, thereby limiting the health risks it poses. Private wells were not tested during this study, however, more than half a million people get their drinking water from private wells that tap the Cambrian-Ordovician aquifer. These homeowners might consider having their water tested for radium.
Curious to learn more about groundwater quality near you? Learn about groundwater quality in 22 Principal Aquifers in nine regions across the United States in informative circulars filled with figures, photos, and water-quality information.
- Science
Visit the web pages below to learn more about groundwater quality across the United States and the factors that affect it.
Groundwater Quality in Principal Aquifers of the Nation, 1991–2010
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. - Data
Access the data releases in this topic here. Explore more data releases on groundwater quality at ScienceBase.
Filter Total Items: 13No Result Found - Publications
Below, you’ll find the latest in peer-reviewed journal articles and USGS reports on groundwater-quality in the Nation’s principal aquifers. For more publications on groundwater quality, look here or search the USGS Publications Warehouse. Look here for help using the Pubs Warehouse.
Tritium as an indicator of modern, mixed, and premodern groundwater age
Categorical classification of groundwater age is often used for the assessment and understanding of groundwater resources. This report presents a tritium-based age classification system for the conterminous United States based on tritium (3H) thresholds that vary in space and time: modern (recharged in 1953 or later), if the measured value is larger than an upper threshold; premodern (recharged prAuthorsBruce D. Lindsey, Bryant C. Jurgens, Kenneth BelitzFilter Total Items: 60Predicting redox conditions in groundwater at a regional scale
Defining the oxic-suboxic interface is often critical for determining pathways for nitrate transport in groundwater and to streams at the local scale. Defining this interface on a regional scale is complicated by the spatial variability of reaction rates. The probability of oxic groundwater in the Chesapeake Bay watershed was predicted by relating dissolved O2 concentrations in groundwater samplesAuthorsAnthony J. Tesoriero, Silvia Terziotti, Daniel B. AbramsThe quality of our Nation's waters: groundwater quality in the Columbia Plateau and Snake River Plain basin-fill and basaltic-rock aquifers and the Hawaiian volcanic-rock aquifers, Washington, Idaho, and Hawaii, 1993-2005
The Columbia Plateau, Snake River Plain, and Hawaii are large volcanic areas in the western United States and mid-Pacific ocean that contain extensive regional aquifers of a hard, gray, volcanic rock called basalt. Residents of the Columbia Plateau, the Snake River Plain, and the island of Oahu depend on groundwater as their primary source of drinking water. Although the depth to the water table cAuthorsMichael G. Rupert, Charles D. Hunt, Kenneth D. Skinner, Lonna M. Frans, Barbara MahlerThe quality of our Nation's waters: water quality in the glacial aquifer system, northern United States, 1993-2009
The glacial aquifer system underlies much of the northern United States. About one-sixth (41 million people) of the United States population relies on the glacial aquifer system for drinking water. The primary importance of the glacial aquifer system is as a source of water for public supply to the population centers in the region, but the aquifer system also provides drinking water for domestic uAuthorsKelly L. Warner, Joseph D. AyotteThe quality of our Nation's waters: water quality in the Northern Atlantic Coastal Plain surficial aquifer system, Delaware, Maryland, New Jersey, New York, North Carolina, and Virginia, 1988-2009
The surficial aquifer system of the Northern Atlantic Coastal Plain is made up of unconfined aquifers that underlie most of the area. This aquifer system is a critical renewable source of drinking water and is the source of most flow to streams and of recharge to underlying confined aquifers. Millions of people rely on the surficial aquifer system for public and domestic water supply, in particulaAuthorsJudith M. Denver, Scott W. Ator, Jeffrey M. Fischer, Douglas C. Harned, Christopher Schubert, Zoltan SzaboThe quality of our Nation's waters: Water quality in basin-fill aquifers of the southwestern United States: Arizona, California, Colorado, Nevada, New Mexico, and Utah, 1993-2009
The Southwest Principal Aquifers consist of many basin-fill aquifers in California, Nevada, Utah, Arizona, New Mexico, and Colorado. Demands for irrigation and drinking water have substantially increased groundwater withdrawals and irrigation return flow to some of these aquifers. These changes have increased the movement of contaminants from geologic and human sources to depths used to supply driAuthorsSusan A. Thiros, Angela P. Paul, Laura M. Bexfield, David W. AnningThe quality of our nation's waters: water quality in the Principal Aquifers of the Piedmont, Blue Ridge, and Valley and Ridge regions, eastern United States, 1993-2009
The aquifers of the Piedmont, Blue Ridge, and Valley and Ridge regions underlie an area with a population of more than 40 million people in 10 states. The suburban and rural population is large, growing rapidly, and increasingly dependent on groundwater as a source of supply, with more than 550 million gallons per day withdrawn from domestic wells for household use. Water from some of these aquifeAuthorsBruce D. Lindsey, Tammy M. Zimmerman, Melinda J. Chapman, Charles A. Cravotta, Zoltan SzaboThe quality of our Nation's waters: water quality in the Upper Floridan aquifer and overlying surficial aquifers, southeastern United States, 1993-2010
About 10 million people rely on groundwater from the Upper Floridan and surficial aquifers for drinking water. The Upper Floridan aquifer also is of primary importance to the region as a source of water for irrigation and as a source of crystal clear water that discharges to springs and streams providing recreational and tourist destinations and unique aquatic habitats. The reliance of the regionAuthorsMarian P. Berndt, Brian G. Katz, James A. Kingsbury, Christy A. CrandallThe quality of our Nation's waters: water quality in the Mississippi embayment-Texas coastal uplands aquifer system and Mississippi River Valley alluvial aquifer, south-central United States, 1994-2008
About 8 million people rely on groundwater from the Mississippi embayment—Texas coastal uplands aquifer system for drinking water. The Mississippi River Valley alluvial aquifer also provides drinking water for domestic use in rural areas but is of primary importance to the region as a source of water for irrigation. Irrigation withdrawals from this aquifer are among the largest in the Nation and pAuthorsJames A. Kingsbury, Jeannie R. B. Barlow, Brian G. Katz, Heather L. Welch, Roland W. Tollett, Lynne S. FahlquistGroundwater studies: principal aquifer surveys
In 1991, the U.S. Congress established the National Water-Quality Assessment (NAWQA) program within the U.S. Geological Survey (USGS) to develop nationally consistent long-term datasets and provide information about the quality of the Nation’s streams and groundwater. The USGS uses objective and reliable data, water-quality models, and systematic scientific studies to assess current water-qualityAuthorsKaren R. Burow, Kenneth BelitzTrends in groundwater quality in principal aquifers of the United States, 1988-2012
The U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program analyzed trends in groundwater quality throughout the nation for the sampling period of 1988-2012. Trends were determined for networks (sets of wells routinely monitored by the USGS) for a subset of constituents by statistical analysis of paired water-quality measurements collected on a near-decadal time scale. TAuthorsBruce D. Lindsey, Michael G. RupertThe quality of our Nation's waters: Water quality in the Denver Basin aquifer system, Colorado, 2003-05
Availability and sustainability of groundwater in the Denver Basin aquifer system depend on water quantity and water quality. The Denver Basin aquifer system underlies about 7,000 square miles of the Great Plains in eastern Colorado and is the primary or sole source of water for domestic and public supply in many areas of the basin. Use of groundwater from the Denver Basin sandstone aquifers has bAuthorsNancy J. Bauch, MaryLynn Musgrove, Barbara Mahler, Suzanne PaschkeWater Quality in the High Plains Aquifer, Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming, 1999-2004
This report contains the major findings of a 1999-2004 assessment of water quality in the High Plains aquifer. It is one of a series of reports by the National Water-Quality Assessment (NAWQA) Program that present major findings for principal and other aquifers and major river basins across the Nation. In these reports, water quality is discussed in terms of local, regional, State, and national isAuthorsJason J. Gurdak, Peter B. McMahon, Kevin Dennehy, Sharon L. Qi - News
Below are news stories associated with this project.
Contaminants present in many parts of the Glacial aquifer system
Are you one of 30 million Americans whose drinking-water supply relies on groundwater from the glacial aquifer system? A new USGS study assesses the quality of untreated groundwater from this critical water resource, which underlies parts of 25 northern U.S. states.
Filter Total Items: 16