Predicting Groundwater Quality in Unmonitored Areas Active
Using Maps and Models to Predict Groundwater Quality
Where do contaminants occur and at what concentrations?
Groundwater provides nearly one-half of the Nation’s drinking water, and sustains the steady flow of streams and rivers and the ecological systems that depend on that flow. Unless we drill a well, how can we know the quality of the groundwater below? Learn about how the USGS is using sophisticated techniques to predict groundwater quality and view national maps of groundwater quality.
Featured: 3-D Models of As and Mn in the Glacial Aquifer System
New 3-D models from the USGS National Water Quality Program predict where high concentrations of arsenic and manganese likely occur in the glacial aquifer system, groundwater supply for 30 million. Redox conditions and pH are controlling factors.
Featured: Predicting Groundwater Age in the Glacial Aquifer System
A new 3-D model predicts groundwater age at all depths across the 25-state span of the glacial aquifer system, reports a new USGS study. About 80% of the groundwater is less than 65 years old, so it's vulnerable to anthropogenic contamination.
Although groundwater is a safe, reliable source of drinking water for millions of people nationwide, high concentrations of some chemical constituents can pose potential human-health concerns. Some of these contaminants come from the rocks and sediments of the aquifers themselves, and others are chemicals that we use in agriculture, industry, and day-to-day life. When groundwater supplies are contaminated, millions of dollars can be required for treatment so that the supplies can be usable. Contaminants in groundwater can also affect the health of our streams and valuable coastal waters. By knowing where contaminants occur in groundwater, what factors control contaminant concentrations, and what kinds of changes in groundwater quality might be expected in the future, we can ensure the availability and quality of this vital natural resource in the future.
At the USGS, researchers are using information from gathered from thousands of wells across the nation to determine how myriad factors, from groundwater age to pesticide use, affect which chemical constituents are dissolved in groundwater and at what concentrations. The constituents include trace elements, such as arsenic and manganese; radionuclides, such as radon and uranium; nutrients, such as nitrate and phosphorus; and manmade chemicals, such as the herbicide atrazine. At elevated concentrations, some of these constituents in drinking water can pose a threat to human health. Others are simply a nuisance, causing drinking water to have an unpleasant smell, taste, or appearance; cause skin or tooth discoloration; or cause corrosion or sedimentation of plumbing.
National Maps of Groundwater Quality
By combining data on the concentrations of chemical constituents measured in thousands of wells, locations of contaminant sources, and factors that affect how a constituent behaves in groundwater, scientists can use sophisticated statistical approaches to predict where a constituent is likely to occur in groundwater and at what concentration. These maps can be used by water resource managers to (1) anticipate water quality in unsampled areas or depth zones, (2) design targeted monitoring programs, (3) inform groundwater protection strategies, and (4) evaluate the sustainability of groundwater sources of drinking water.
View regional and national maps for the following chemical constituents and contaminants:
- Arsenic concentrations in the basin-fill aquifers of the Southwest
- Nitrate concentrations in shallow groundwater and deep groundwater used for drinking across the Nation
- Atrazine concentrations in shallow groundwater beneath agricultural land across the Nation
Mapping Groundwater Quality in 3-D
Just as the characteristics of an aquifer can vary greatly with depth, so can the quality of the groundwater. Domestic wells, such as those used by homeowners, typically pump groundwater from relatively shallow depths. Public-supply wells that serve many thousands of people typically pump groundwater from much greater depths—sometimes hundreds of feet or more.
Three-dimensional, or 3-D, depictions of groundwater quality are being developed for four Principal Aquifers: the Glacial Aquifer system, which extends across the northernmost one-third of the United States; the Central Valley aquifer, in California; the Mississippi Embayment aquifer in south-central U.S.; and the Northern Atlantic Coastal Plain aquifer, in the southeast. These depictions focus on groundwater quality at depths tapped by domestic-supply wells and public-supply wells. The information gained also will be used to assess the vulnerability of streams to contaminants derived from groundwater in these areas.
The web pages below are gateways to more USGS research on the Nation’s groundwater quality.
Groundwater Quality Research
Groundwater/Surface-Water Interaction
Public Supply Wells
Domestic (Private) Supply Wells
Radionuclides
Groundwater Quality in Principal Aquifers of the Nation, 1991–2010
Factors Affecting Vulnerability of Public-Supply Wells to Contamination
Groundwater Age
Volatile Organic Compounds (VOCs)
Oxidation/Reduction (Redox)
Access data for the Groundwater Mapping and Modeling study from the data releases listed below. Explore more data on groundwater quality at Science Base.
Depth to 50 percent probability of oxic conditions, Chesapeake Bay Watershed
Ascii grids of predicted pH in depth zones used by domestic and public drinking water supply depths, Central Valley, California
Take a deep dive into the science of predicting groundwater quality with the publications below. Find more publications on groundwater quality here.
Predicting arsenic in drinking water wells of the Central Valley, California
Three-dimensional distribution of residence time metrics in the glaciated United States using metamodels trained on general numerical models
Machine learning predictions of pH in the Glacial Aquifer System, Northern USA
Extraction and development of inset models in support of groundwater age calculations for glacial aquifers
Metamodeling and mapping of nitrate flux in the unsaturated zone and groundwater, Wisconsin, USA
Regional variability of nitrate fluxes in the unsaturated zone and groundwater, Wisconsin, USA
Estimating the high-arsenic domestic-well population in the conterminous United States
Fraction of young water as an indicator of aquifer vulnerability along two regional flow paths in the Mississippi embayment aquifer system, southeastern USA
Predicting redox-sensitive contaminant concentrations in groundwater using random forest classification
A hybrid machine learning model to predict and visualize nitrate concentration throughout the Central Valley aquifer, California, USA
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
Predicting arsenic in drinking water wells of the Central Valley, California
Access data for the Groundwater Mapping and Modeling study from the data releases listed below. Explore more data on groundwater quality at Science Base.
Groundwater Quality: Decadal Change
Almost one-half of the U.S. population rely on groundwater for their water supply, and demand for groundwater for public supply, irrigation, and agriculture continues to increase. This mapper shows how concentrations of pesticides, nutrients, metals, and organic contaminants in groundwater are changing during decadal periods across the Nation.
Below are news stories associated with this project.
- Overview
Groundwater provides nearly one-half of the Nation’s drinking water, and sustains the steady flow of streams and rivers and the ecological systems that depend on that flow. Unless we drill a well, how can we know the quality of the groundwater below? Learn about how the USGS is using sophisticated techniques to predict groundwater quality and view national maps of groundwater quality.
Featured: 3-D Models of As and Mn in the Glacial Aquifer SystemNew 3-D models from the USGS National Water Quality Program predict where high concentrations of arsenic and manganese likely occur in the glacial aquifer system, groundwater supply for 30 million. Redox conditions and pH are controlling factors.
Featured: Predicting Groundwater Age in the Glacial Aquifer SystemA new 3-D model predicts groundwater age at all depths across the 25-state span of the glacial aquifer system, reports a new USGS study. About 80% of the groundwater is less than 65 years old, so it's vulnerable to anthropogenic contamination.
Although groundwater is a safe, reliable source of drinking water for millions of people nationwide, high concentrations of some chemical constituents can pose potential human-health concerns. Some of these contaminants come from the rocks and sediments of the aquifers themselves, and others are chemicals that we use in agriculture, industry, and day-to-day life. When groundwater supplies are contaminated, millions of dollars can be required for treatment so that the supplies can be usable. Contaminants in groundwater can also affect the health of our streams and valuable coastal waters. By knowing where contaminants occur in groundwater, what factors control contaminant concentrations, and what kinds of changes in groundwater quality might be expected in the future, we can ensure the availability and quality of this vital natural resource in the future.
At the USGS, researchers are using information from gathered from thousands of wells across the nation to determine how myriad factors, from groundwater age to pesticide use, affect which chemical constituents are dissolved in groundwater and at what concentrations. The constituents include trace elements, such as arsenic and manganese; radionuclides, such as radon and uranium; nutrients, such as nitrate and phosphorus; and manmade chemicals, such as the herbicide atrazine. At elevated concentrations, some of these constituents in drinking water can pose a threat to human health. Others are simply a nuisance, causing drinking water to have an unpleasant smell, taste, or appearance; cause skin or tooth discoloration; or cause corrosion or sedimentation of plumbing.National Maps of Groundwater Quality
By combining data on the concentrations of chemical constituents measured in thousands of wells, locations of contaminant sources, and factors that affect how a constituent behaves in groundwater, scientists can use sophisticated statistical approaches to predict where a constituent is likely to occur in groundwater and at what concentration. These maps can be used by water resource managers to (1) anticipate water quality in unsampled areas or depth zones, (2) design targeted monitoring programs, (3) inform groundwater protection strategies, and (4) evaluate the sustainability of groundwater sources of drinking water.
View regional and national maps for the following chemical constituents and contaminants:
- Arsenic concentrations in the basin-fill aquifers of the Southwest
- Nitrate concentrations in shallow groundwater and deep groundwater used for drinking across the Nation
- Atrazine concentrations in shallow groundwater beneath agricultural land across the Nation
Mapping Groundwater Quality in 3-D
Just as the characteristics of an aquifer can vary greatly with depth, so can the quality of the groundwater. Domestic wells, such as those used by homeowners, typically pump groundwater from relatively shallow depths. Public-supply wells that serve many thousands of people typically pump groundwater from much greater depths—sometimes hundreds of feet or more.
Three-dimensional, or 3-D, depictions of groundwater quality are being developed for four Principal Aquifers: the Glacial Aquifer system, which extends across the northernmost one-third of the United States; the Central Valley aquifer, in California; the Mississippi Embayment aquifer in south-central U.S.; and the Northern Atlantic Coastal Plain aquifer, in the southeast. These depictions focus on groundwater quality at depths tapped by domestic-supply wells and public-supply wells. The information gained also will be used to assess the vulnerability of streams to contaminants derived from groundwater in these areas. - Science
The web pages below are gateways to more USGS research on the Nation’s groundwater quality.
Groundwater Quality Research
Every day, millions of gallons of groundwater are pumped to supply drinking water for about 140 million people, almost one-half of the Nation’s population. Learn about the quality and availability of groundwater for drinking, where and why groundwater quality is degraded, and where groundwater quality is changing.Groundwater/Surface-Water Interaction
Water and the chemicals it contains are constantly being exchanged between the land surface and the subsurface. Surface water seeps into the ground and recharges the underlying aquifer—groundwater discharges to the surface and supplies the stream with baseflow. USGS Integrated Watershed Studies assess these exchanges and their effect on surface-water and groundwater quality and quantity.Public Supply Wells
Are you among the more than 100 million people in the U.S. who relies on a public-supply well for your drinking water? Although the quality of finished drinking water from public water systems is regulated by the EPA, long-term protection and management of the raw groundwater tapped by public-supply wells requires an understanding of the occurrence of contaminants in this invisible, vital resource...Domestic (Private) Supply Wells
More than 43 million people—about 15 percent of the U.S. population—rely on domestic (private) wells as their source of drinking water. The quality and safety of water from domestic wells are not regulated by the Federal Safe Drinking Water Act or, in most cases, by state laws. Instead, individual homeowners are responsible for maintaining their domestic well systems and for monitoring water...Radionuclides
Many people might be surprised to learn that drinking-water sources, especially groundwater, can contain radioactive elements (radionuclides). Radionuclides in water can be a concern for human health because several are toxic or carcinogenic. Other radionuclides are useful tools for determining the age of groundwater in an aquifer or of sediment deposited at the bottom of a water body.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.Factors Affecting Vulnerability of Public-Supply Wells to Contamination
More than 100 million people in the United States—about 35 percent of the population—receive their drinking water from public-supply wells. These systems can be vulnerable to contamination from naturally occurring constituents, such as radon, uranium and arsenic, and from commonly used manmade chemicals, such as fertilizers, pesticides, solvents, and gasoline hydrocarbons. Learn about the...Groundwater Age
The age of groundwater is key in predicting which contaminants it might contain. There are many tracers and techniques that allow us to estimate the age—or mix of ages—of the groundwater we depend on as a drinking water supply.Volatile Organic Compounds (VOCs)
Volatile organic compounds (VOCs) are chemicals that both vaporize into air and dissolve in water. VOCs are pervasive in daily life, because they’re used in industry, agriculture, transportation, and day-to-day activities around the home. Once released into groundwater, many VOCs are persistent and can migrate to drinking-water supply wells.Oxidation/Reduction (Redox)
The redox state of groundwater—whether the groundwater is oxic (oxidized) or anoxic (reduced)—has profound implications for groundwater quality. Knowing the redox conditions of groundwater can help determine whether it contains elevated levels of many contaminants, including arsenic, nitrate, and even some manmade contaminants. - Data
Access data for the Groundwater Mapping and Modeling study from the data releases listed below. Explore more data on groundwater quality at Science Base.
Depth to 50 percent probability of oxic conditions, Chesapeake Bay Watershed
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 samplesAscii grids of predicted pH in depth zones used by domestic and public drinking water supply depths, Central Valley, California
The ascii grids associated with this data release are predicted distributions of continuous pH at the drinking water depth zones in the groundwater of Central Valley, California. The two prediction grids produced in this work represent predicted pH at the domestic supply and public supply drinking water depths, respectively and are bound by the alluvial boundary that defines the Central Valley. A - Publications
Take a deep dive into the science of predicting groundwater quality with the publications below. Find more publications on groundwater quality here.
Predicting 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. GronbergFilter Total Items: 16Three-dimensional distribution of residence time metrics in the glaciated United States using metamodels trained on general numerical models
Residence time distribution (RTD) is a critically important characteristic of groundwater flow systems; however, it cannot be measured directly. RTD can be inferred from tracer data with analytical models (few parameters) or with numerical models (many parameters). The second approach permits more variation in system properties but is used less frequently than the first because large‐scale numericAuthorsJ. Jeffrey Starn, Leon J. Kauffman, Carl S. Carlson, James E. Reddy, Michael N. FienenMachine learning predictions of pH in the Glacial Aquifer System, Northern USA
A boosted regression tree model was developed to predict pH conditions in three dimensions throughout the glacial aquifer system of the contiguous United States using pH measurements in samples from 18,386 wells and predictor variables that represent aspects of the hydrogeologic setting. Model results indicate that the carbonate content of soils and aquifer materials strongly controls pH and, whenAuthorsPaul Stackelberg, Kenneth Belitz, Craig J. Brown, Melinda L. Erickson, Sarah M. Elliott, Leon J. Kauffman, Katherine Marie Ransom, James E. ReddyExtraction and development of inset models in support of groundwater age calculations for glacial aquifers
The U.S. Geological Survey developed a regional model of Lake Michigan Basin (LMB). This report describes the construction of five MODFLOW inset models extracted from the LMB regional model and their application using the particle-tracking code MODPATH to simulate the groundwater age distribution of discharge to wells pumping from glacial deposits. The five study areas of the inset model corresponAuthorsDaniel T. Feinstein, Leon J. Kauffman, Megan J. Haserodt, Brian R. Clark, Paul F. JuckemMetamodeling 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. ReddyRegional variability of nitrate fluxes in the unsaturated zone and groundwater, Wisconsin, USA
Process-based modeling of regional NO3− fluxes to groundwater is critical for understanding and managing water quality, but the complexity of NO3− reactive transport processes make implementation a challenge. This study introduces a regional vertical flux method (VFM) for efficient estimation of reactive transport of NO3− in the vadose zone and groundwater. The regional VFM was applied to 443 wellAuthorsChristopher T. Green, Lixia Liao, Bernard T. Nolan, Paul F. Juckem, Christopher L. Shope, Anthony J. Tesoriero, Bryant C. JurgensEstimating the high-arsenic domestic-well population in the conterminous United States
Arsenic concentrations from 20 450 domestic wells in the U.S. were used to develop a logistic regression model of the probability of having arsenic >10 μg/L (“high arsenic”), which is presented at the county, state, and national scales. Variables representing geologic sources, geochemical, hydrologic, and physical features were among the significant predictors of high arsenic. For U.S. Census blocAuthorsJoseph D. Ayotte, Laura Medalie, Sharon L. Qi, Lorraine C. Backer, Bernard T. NolanFraction of young water as an indicator of aquifer vulnerability along two regional flow paths in the Mississippi embayment aquifer system, southeastern USA
Wells along two regional flow paths were sampled to characterize changes in water quality and the vulnerability to contamination of the Memphis aquifer across a range of hydrologic and land-use conditions in the southeastern United States. The flow paths begin in the aquifer outcrop area and end at public supply wells in the confined parts of the aquifer at Memphis, Tennessee. Age-date tracer (e.gAuthorsJames A. Kingsbury, Jeannie R. B. Barlow, Bryant C. Jurgens, Peter B. McMahon, John K. CarmichaelPredicting redox-sensitive contaminant concentrations in groundwater using random forest classification
Machine learning techniques were applied to a large (n > 10,000) compliance monitoring database to predict the occurrence of several redox-active constituents in groundwater across a large watershed. Specifically, random forest classification was used to determine the probabilities of detecting elevated concentrations of nitrate, iron, and arsenic in the Fox, Wolf, Peshtigo, and surrounding watersAuthorsAnthony J. Tesoriero, Jo Ann M. Gronberg, Paul F. Juckem, Matthew P. Miller, Brian P. AustinA hybrid machine learning model to predict and visualize nitrate concentration throughout the Central Valley aquifer, California, USA
Intense demand for water in the Central Valley of California and related increases in groundwater nitrate concentration threaten the sustainability of the groundwater resource. To assess contamination risk in the region, we developed a hybrid, non-linear, machine learning model within a statistical learning framework to predict nitrate contamination of groundwater to depths of approximately 500 mAuthorsKatherine M. Ransom, Bernard T. Nolan, Jonathan A. Traum, Claudia C. Faunt, Andrew M. Bell, Jo Ann M. Gronberg, David C. Wheeler, Celia Zamora, Bryant C. Jurgens, Gregory E. Schwarz, Kenneth Belitz, Sandra M. Eberts, George Kourakos, Thomas HarterSimulation 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. GronbergPredicting 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. Gronberg - Web Tools
Access data for the Groundwater Mapping and Modeling study from the data releases listed below. Explore more data on groundwater quality at Science Base.
Groundwater Quality: Decadal Change
Almost one-half of the U.S. population rely on groundwater for their water supply, and demand for groundwater for public supply, irrigation, and agriculture continues to increase. This mapper shows how concentrations of pesticides, nutrients, metals, and organic contaminants in groundwater are changing during decadal periods across the Nation.
- News
Below are news stories associated with this project.