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.
Langelier Saturation Indices Computed for U.S. Groundwater, 1991-2015; Water Well Data and Characteristic Values for States
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
Guidelines and standard procedures for high-frequency groundwater-quality monitoring stations—Design, operation, and record computation
Arsenic variability and groundwater age in three water supply wells in southeast New Hampshire
Drinking water quality in the glacial aquifer system, northern USA
Timescales of water-quality change in a karst aquifer, south-central Texas
Hydrocarbons in upland groundwater, Marcellus Shale Region, Northeastern Pennsylvania and Southern New York, USA
Assessing the lead solubility potential of untreated groundwater of the United States
Hormones and pharmaceuticals in groundwater used as a source of drinking water across the United States
Elevated manganese concentrations in United States groundwater, role of land surface–soil–aquifer connections
Tritium deposition in precipitation in the United States, 1953–2012
Secondary hydrogeologic regions of the conterminous United States
Groundwater-quality and select quality-control data from the National Water-Quality Assessment Project, January through December 2015, and previously unpublished data from 2013 to 2014
Metamodeling and mapping of nitrate flux in the unsaturated zone and groundwater, Wisconsin, USA
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: 13Langelier Saturation Indices Computed for U.S. Groundwater, 1991-2015; Water Well Data and Characteristic Values for States
The occurrence of metals, such as lead and copper, in household drinking supplies can often be a result of the corrosion of pipes and joints in water distribution systems. One measure of the potential for water to cause corrosion is the Langelier Saturation Index (LSI) (Langelier, 1936). The LSI is a measure of the potential for water to deposit a mineral layer (scale) within a water distribution - 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: 60Guidelines and standard procedures for high-frequency groundwater-quality monitoring stations—Design, operation, and record computation
High-frequency water-quality monitoring stations measure and transmit data, often in near real-time, from a wide range of aquatic environments to assess the quality of the Nation’s water resources. Common instrumentation for high-frequency water-quality data collection uses a multi-parameter sonde, which typically has sensors that measure and record water temperature, specific conductance, pH, andAuthorsTimothy M. Mathany, John Franco Saraceno, Justin T. KulongoskiArsenic variability and groundwater age in three water supply wells in southeast New Hampshire
Three wells in New Hampshire were sampled bimonthly over three years to evaluate the temporal variability of arsenic concentrations and groundwater age. All samples had measurable concentrations of arsenic throughout the entire sampling period and concentrations in individual wells varied, on average, by more than 7 µg/L. High arsenic concentrations (>10 µg/L) were measured in bedrock wells KFW-87AuthorsJoseph Levitt, James Degnan, Sarah Flanagan, Bryant JurgensDrinking water quality in the glacial aquifer system, northern USA
Groundwater supplies 50% of drinking water worldwide, but compromised water quality from anthropogenic and geogenic contaminants can limit usage of groundwater as a drinking water source. Groundwater quality in the glacial aquifer system, USA (GLAC), is presented in the context of a hydrogeologic framework that divides the study area into 17 hydrogeologic terranes. Results are reported at aquifer-AuthorsMelinda L. Erickson, Richard M. Yager, Leon J. Kauffman, John T. WilsonTimescales of water-quality change in a karst aquifer, south-central Texas
Understanding the drivers and timescales over which groundwater quality changes informs groundwater management, use, and protection. To better understand timescales of water-quality change over short (daily to monthly) and long (seasonal to decadal) timescales, the U.S. Geological Survey’s National Water-Quality Assessment (NAWQA) Enhanced Trends Network (ETN) program instrumented and sampled threAuthorsMaryLynn Musgrove, John E. Solder, Stephen P. Opsahl, Jennifer T. WilsonHydrocarbons in upland groundwater, Marcellus Shale Region, Northeastern Pennsylvania and Southern New York, USA
Water samples from 50 domestic wells located <1 km (proximal) and >1 km (distal) from shale-gas wells in upland areas of the Marcellus Shale region were analyzed for chemical, isotopic, and groundwater-age tracers. Uplands were targeted because natural mixing with brine and hydrocarbons from deep formations is less common in those areas compared to valleys. CH4-isotope, predrill CH4-concentration,AuthorsPeter B. McMahon, Bruce D. Lindsey, Matthew D. Conlon, Andrew G. Hunt, Kenneth Belitz, Bryant Jurgens, Brian A. VarelaByWater Resources Mission Area, Energy Resources Program, National Water Quality Program, California Water Science Center, Central Energy Resources Science Center, Colorado Water Science Center, Geology, Geophysics, and Geochemistry Science Center, Geology, Minerals, Energy, and Geophysics Science Center, New England Water Science Center, Pennsylvania Water Science CenterAssessing the lead solubility potential of untreated groundwater of the United States
In the U.S., about 44 million people rely on self-supplied groundwater for drinking water. Because most self-supplied homeowners do not treat their water to control corrosion, drinking water can be susceptible to lead (Pb) contamination from metal plumbing. To assess the types and locations of susceptible groundwater, a geochemical reaction model that included pure Pb minerals and solid solutionsAuthorsBryant Jurgens, David L. Parkhurst, Kenneth BelitzHormones and pharmaceuticals in groundwater used as a source of drinking water across the United States
This is the first large-scale, systematic assessment of hormone and pharmaceutical occurrence in groundwater used for drinking across the United States. Samples from 1091 sites in Principal Aquifers representing 60% of the volume pumped for drinking-water supply had final data for 21 hormones and 103 pharmaceuticals. At least one compound was detected at 5.9% of 844 sites representing the resourceAuthorsLaura M. Bexfield, Patricia Toccalino, Kenneth Belitz, William T. Foreman, Edward FurlongElevated manganese concentrations in United States groundwater, role of land surface–soil–aquifer connections
Chemical data from 43 334 wells were used to examine the role of land surface–soil–aquifer connections in producing elevated manganese concentrations (>300 μg/L) in United States (U.S.) groundwater. Elevated concentrations of manganese and dissolved organic carbon (DOC) in groundwater are associated with shallow, anoxic water tables and soils enriched in organic carbon, suggesting soil-derived DOCAuthorsPeter B. McMahon, Kenneth Belitz, James E. Reddy, Tyler D. JohnsonTritium deposition in precipitation in the United States, 1953–2012
Tritium is a radioactive isotope of hydrogen (half-life is equal to 12.32 years). Since it is part of the water molecule, tritium can be used to track and date groundwater and surface water when the history of tritium in precipitation and recharge is known. To facilitate that effort, tritium concentrations in precipitation were reconstructed from measurements and correlations for 10 precipitationAuthorsRobert L. Michel, Bryant C. Jurgens, Megan B. YoungSecondary hydrogeologic regions of the conterminous United States
The U.S. Geological Survey (USGS) previously identified and mapped 62 Principal Aquifers (PAs) in the U.S., with 57 located in the conterminous states. Areas outside of PAs, which account for about 40% of the conterminous U.S., were collectively identified as “other rocks.” This paper, for the first time, subdivides this large area into internally-consistent features, defined here as Secondary HAuthorsKenneth Belitz, Elise Watson, Tyler D. Johnson, Jennifer B. SharpeGroundwater-quality and select quality-control data from the National Water-Quality Assessment Project, January through December 2015, and previously unpublished data from 2013 to 2014
Groundwater-quality data were collected from 502 wells as part of the National Water-Quality Assessment Project of the U.S. Geological Survey National Water-Quality Program and are included in this report. Most of the wells (500) were sampled from January through December 2015, and 2 of them were sampled in 2013. The data were collected from five types of well networks: principal aquifer study netAuthorsTerri Arnold, Laura M. Bexfield, MaryLynn Musgrove, Paul E. Stackelberg, Bruce D. Lindsey, James A. Kingsbury, Justin T. Kulongoski, Kenneth BelitzMetamodeling and mapping of nitrate flux in the unsaturated zone and groundwater, Wisconsin, USA
Nitrate contamination of groundwater in agricultural areas poses a major challenge to the sustainability of water resources. Aquifer vulnerability models are useful tools that can help resource managers identify areas of concern, but quantifying nitrogen (N) inputs in such models is challenging, especially at large spatial scales. We sought to improve regional nitrate (NO3−) input functions by chaAuthorsBernard T. Nolan, Christopher T. Green, Paul F. Juckem, Lixia Liao, James E. Reddy - 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.
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