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
Methane and benzene in drinking-water wells overlying the Eagle Ford, Fayetteville, and Haynesville Shale hydrocarbon production areas
Simulation of groundwater flow in the glacial aquifer system of northeastern Wisconsin with variable model complexity
Prediction and visualization of redox conditions in the groundwater of Central Valley, California
Using groundwater age distributions to understand changes in methyl tert-butyl ether (MtBE) concentrations in ambient groundwater, northeastern United States
Large decadal-scale changes in uranium and bicarbonate in groundwater of the irrigated western U.S
Potential corrosivity of untreated groundwater in the United States
Predicting arsenic in drinking water wells of the Central Valley, California
Groundwater quality in the Coastal Lowlands aquifer system, south-central United States
Groundwater quality in the Northern Atlantic Coastal Plain aquifer system, eastern United States
Groundwater quality in the Valley and Ridge and Piedmont and Blue Ridge carbonate-rock aquifers, eastern United States
Groundwater quality in the Basin and Range Basin-Fill Aquifers, southwestern United States
Groundwater quality in the Southeastern Coastal Plain aquifer system, southeastern United States
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: 60Methane and benzene in drinking-water wells overlying the Eagle Ford, Fayetteville, and Haynesville Shale hydrocarbon production areas
Water wells (n = 116) overlying the Eagle Ford, Fayetteville, and Haynesville Shale hydrocarbon production areas were sampled for chemical, isotopic, and groundwater-age tracers to investigate the occurrence and sources of selected hydrocarbons in groundwater. Methane isotopes and hydrocarbon gas compositions indicate most of the methane in the wells was biogenic and produced by the CO2 reductionAuthorsPeter B. McMahon, Jeannie R. B. Barlow, Mark A. Engle, Kenneth Belitz, Patricia B. Ging, Andrew G. Hunt, Bryant C. Jurgens, Yousif K. Kharaka, Roland W. Tollett, Timothy M. KresseSimulation of groundwater flow in the glacial aquifer system of northeastern Wisconsin with variable model complexity
The U.S. Geological Survey, National Water-Quality Assessment seeks to map estimated intrinsic susceptibility of the glacial aquifer system of the conterminous United States. Improved understanding of the hydrogeologic characteristics that explain spatial patterns of intrinsic susceptibility, commonly inferred from estimates of groundwater age distributions, is sought so that methods used for theAuthorsPaul F. Juckem, Brian R. Clark, Daniel T. FeinsteinPrediction and visualization of redox conditions in the groundwater of Central Valley, California
Regional-scale, three-dimensional continuous probability models, were constructed for aspects of redox conditions in the groundwater system of the Central Valley, California. These models yield grids depicting the probability that groundwater in a particular location will have dissolved oxygen (DO) concentrations less than selected threshold values representing anoxic groundwater conditions, or wiAuthorsCelia Z. Rosecrans, Bernard T. Nolan, JoAnn M. GronbergUsing groundwater age distributions to understand changes in methyl tert-butyl ether (MtBE) concentrations in ambient groundwater, northeastern United States
Temporal changes in methyl tert-butyl ether (MtBE) concentrations in groundwater were evaluated in the northeastern United States, an area of the nation with widespread low-level detections of MtBE based on a national survey of wells selected to represent ambient conditions. MtBE use in the U.S. peaked in 1999 and was largely discontinued by 2007. Six well networks, each representing specific areaAuthorsBruce D. Lindsey, Joseph D. Ayotte, Bryant C. Jurgens, Leslie A. DeSimoneLarge decadal-scale changes in uranium and bicarbonate in groundwater of the irrigated western U.S
Samples collected about one decade apart from 1105 wells from across the U.S. were compiled to assess whether uranium concentrations in the arid climate are linked to changing bicarbonate concentrations in the irrigated western U.S. Uranium concentrations in groundwater were high in the arid climate in the western U.S, where uranium sources are abundant. Sixty-four wells (6%) were above the U.S. EAuthorsKaren R. Burow, Kenneth Belitz, Neil M. Dubrovsky, Bryant C. JurgensPotential corrosivity of untreated groundwater in the United States
Corrosive groundwater, if untreated, can dissolve lead and other metals from pipes and other components in water distribution systems. Two indicators of potential corrosivity—the Langelier Saturation Index (LSI) and the Potential to Promote Galvanic Corrosion (PPGC)—were used to identify which areas in the United States might be more susceptible to elevated concentrations of metals in household drAuthorsKenneth Belitz, Bryant C. Jurgens, Tyler D. JohnsonPredicting arsenic in drinking water wells of the Central Valley, California
Probabilities of arsenic in groundwater at depths used for domestic and public supply in the Central Valley of California are predicted using weak-learner ensemble models (boosted regression trees, BRT) and more traditional linear models (logistic regression, LR). Both methods captured major processes that affect arsenic concentrations, such as the chemical evolution of groundwater, redox differenAuthorsJoseph D. Ayotte, Bernard T. Nolan, JoAnn M. GronbergGroundwater quality in the Coastal Lowlands aquifer system, south-central United States
Groundwater provides nearly 50 percent of the Nation’s drinking water. To help protect this vital resource, the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Project assesses groundwater quality in aquifers that are important sources of drinking water. The Coastal Lowlands aquifer system constitutes one of the important areas being evaluated. One or more inorganic constitAuthorsJeannie R.B. Barlow, Kenneth BelitzGroundwater quality in the Northern Atlantic Coastal Plain aquifer system, eastern United States
Groundwater provides nearly 50 percent of the Nation’s drinking water. To help protect this vital resource, the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Project assesses groundwater quality in aquifers that are important sources of drinking water. The Northern Atlantic Coastal Plain aquifer system constitutes one of the important areas being evaluated. One or more inAuthorsBruce D. Lindsey, Kenneth BelitzGroundwater quality in the Valley and Ridge and Piedmont and Blue Ridge carbonate-rock aquifers, eastern United States
Groundwater provides nearly 50 percent of the Nation’s drinking water. To help protect this vital resource, the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Project assesses groundwater quality in aquifers that are important sources of drinking water. The Valley and Ridge and Piedmont and Blue Ridge carbonate-rock aquifers constitute two of the important areas being evalAuthorsBruce D. Lindsey, Kenneth BelitzGroundwater quality in the Basin and Range Basin-Fill Aquifers, southwestern United States
Groundwater provides nearly 50 percent of the Nation’s drinking water. To help protect this vital resource, the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Project assesses groundwater quality in aquifers that are important sources of drinking water. The Basin and Range basin-fill aquifers constitute one of the important areas being evaluated. One or more inorganic consAuthorsMaryLynn Musgrove, Kenneth BelitzGroundwater quality in the Southeastern Coastal Plain aquifer system, southeastern United States
Groundwater provides nearly 50 percent of the Nation’s drinking water. To help protect this vital resource, the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Project assesses groundwater quality in aquifers that are important sources of drinking water. The Southeastern Coastal Plain aquifer system constitutes one of the important areas being evaluated. One or more inorganAuthorsJeannie Barlow, Bruce D. Lindsey, Kenneth Belitz - 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