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 Transport of Anthropogenic and Naturally Occurring Contaminants (TANC) study.
Public-supply-well vulnerability to contamination starts with groundwater vulnerability to contamination. Even wells within a single aquifer, however, may not be equally vulnerable to contamination because individual wells produce unique mixtures of the groundwater from different parts of the aquifer.
A study done from 2001 to 2011 (Transport of Anthropogenic Contaminants, or TANC study) sheds light on factors that affect the vulnerability of water from public-supply wells to contamination. The study also identified measures that can be used to determine which factor (or factors) plays a dominant role at an individual public-supply well. Case-study examples show how such information can be used to improve water quality.
In general, the vulnerability of the water from public-supply wells to contamination depends on contaminant input in the area that contributes water to a well, the mobility and persistence of a contaminant once released to the groundwater, and the ease of groundwater and contaminant movement from the point of recharge to the well. The following measures are particularly useful for indicating which contaminants in an aquifer might reach an individual public-supply well and when, how, and at what concentration they might arrive:
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Sources of recharge—Information on the sources of recharge for a well provides insight into contaminants that might enter the aquifer with the recharge water and potentially reach the well.
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Geochemical conditions—Information on the geochemical conditions encountered by groundwater traveling to a well provides insight into contaminants that might persist in the water all the way to the well. Use the Redox Framework Tool to determine the redox conditions associated with water from a public-supply well.
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Groundwater-age mixtures—Information on the ages of the different waters that mix in a well provides insight into the time lag between contaminant input at the water table and contaminant arrival at the well. It also provides insight into the potential for in-well dilution of contaminated water by unaffected groundwater of a different age that simultaneously enters the well. Use the web-based Groundwater Age Mixtures and Contaminant Trends Tool to explore the effects of basic aquifer properties and well configurations on groundwater age mixtures in groundwater discharge and on contaminant trends from different nonpoint-source contaminant input scenarios.
Preferential flow pathways—pathways that provide little resistance to flow—can influence how all other factors affect public-supply-well vulnerability to contamination. For example, preferential flow pathways can influence whether a contaminant source is physically linked to a well, whether contaminant concentrations are substantially altered before contaminated groundwater reaches a well, and whether contaminated groundwater can arrive at a well within a timeframe of concern to the well owner. Methods for recognizing the influence of preferential flow pathways on the quality of water from a public-supply well are presented in this circular and can provide opportunities to prevent or mitigate the deterioration of a water supply.
Knowing what water-quality variables to measure, what spatial and temporal scales on which to measure them, and how to interpret the resulting data makes it possible for samples from public-supply wells to provide a broad window into a well’s past and present water quality—and possibly future water quality. Such insight can enable resource managers to prioritize actions for sustaining a high-quality groundwater source of drinking water.
Learn more about the USGS National Water Quality Assessment Project and research on the Nation’s groundwater and surface-water quality.
Look down the list below for additional web resources describing USGS research on groundwater quality.
Public Supply Wells
Domestic (Private) Supply Wells
Groundwater Quality in Principal Aquifers of the Nation, 1991–2010
Rapid Fluctuations in Groundwater Quality
Predicting Groundwater Quality in Unmonitored Areas
- Overview
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 Transport of Anthropogenic and Naturally Occurring Contaminants (TANC) study.
Public-supply-well vulnerability to contamination starts with groundwater vulnerability to contamination. Even wells within a single aquifer, however, may not be equally vulnerable to contamination because individual wells produce unique mixtures of the groundwater from different parts of the aquifer.
A study done from 2001 to 2011 (Transport of Anthropogenic Contaminants, or TANC study) sheds light on factors that affect the vulnerability of water from public-supply wells to contamination. The study also identified measures that can be used to determine which factor (or factors) plays a dominant role at an individual public-supply well. Case-study examples show how such information can be used to improve water quality.
Sources/Usage: Public Domain.U.S. Geological Survey (USGS) scientists studying the vulnerability of public-supply wells to contamination have identified ways in which the seasonal operation of public-supply wells can affect the quality of water that they produce. (Credit: Cathy Munday, USGS.) In general, the vulnerability of the water from public-supply wells to contamination depends on contaminant input in the area that contributes water to a well, the mobility and persistence of a contaminant once released to the groundwater, and the ease of groundwater and contaminant movement from the point of recharge to the well. The following measures are particularly useful for indicating which contaminants in an aquifer might reach an individual public-supply well and when, how, and at what concentration they might arrive:
-
Sources of recharge—Information on the sources of recharge for a well provides insight into contaminants that might enter the aquifer with the recharge water and potentially reach the well.
-
Geochemical conditions—Information on the geochemical conditions encountered by groundwater traveling to a well provides insight into contaminants that might persist in the water all the way to the well. Use the Redox Framework Tool to determine the redox conditions associated with water from a public-supply well.
-
Groundwater-age mixtures—Information on the ages of the different waters that mix in a well provides insight into the time lag between contaminant input at the water table and contaminant arrival at the well. It also provides insight into the potential for in-well dilution of contaminated water by unaffected groundwater of a different age that simultaneously enters the well. Use the web-based Groundwater Age Mixtures and Contaminant Trends Tool to explore the effects of basic aquifer properties and well configurations on groundwater age mixtures in groundwater discharge and on contaminant trends from different nonpoint-source contaminant input scenarios.
Preferential flow pathways—pathways that provide little resistance to flow—can influence how all other factors affect public-supply-well vulnerability to contamination. For example, preferential flow pathways can influence whether a contaminant source is physically linked to a well, whether contaminant concentrations are substantially altered before contaminated groundwater reaches a well, and whether contaminated groundwater can arrive at a well within a timeframe of concern to the well owner. Methods for recognizing the influence of preferential flow pathways on the quality of water from a public-supply well are presented in this circular and can provide opportunities to prevent or mitigate the deterioration of a water supply.
Knowing what water-quality variables to measure, what spatial and temporal scales on which to measure them, and how to interpret the resulting data makes it possible for samples from public-supply wells to provide a broad window into a well’s past and present water quality—and possibly future water quality. Such insight can enable resource managers to prioritize actions for sustaining a high-quality groundwater source of drinking water.
Learn more about the USGS National Water Quality Assessment Project and research on the Nation’s groundwater and surface-water quality.
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- Science
Look down the list below for additional web resources describing USGS research on groundwater quality.
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...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.Rapid Fluctuations in Groundwater Quality
We think of groundwater as moving slowly, and groundwater quality as changing slowly—over decades or even centuries. But in some parts of some aquifers, groundwater quality can fluctuate rapidly, sometimes over just a few hours. Are such changes part of a long-term trend, or just part of a short-term cycle? And what does that mean for suitability for drinking?Predicting Groundwater Quality in Unmonitored Areas
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. - Publications