Factors Affecting Vulnerability of Public-Supply Wells to Contamination Completed
Insights into Water Quality at Public-Supply Wells
Understanding observed water quality and anticipating future water quality
Groundwater Age Mixtures and Contaminant Trends Tool
Explore the effects of groundwater age mixtures on contaminant trends
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
Access publication on groundwater vulnerability to contamination below. For more publications on groundwater quality, search the USGS Publications Warehouse. Look here for help using the Pubs Warehouse.
The quality of our Nation's waters: factors affecting public-supply-well vulnerability to contamination: understanding observed water quality and anticipating future water quality
Using Cl/Br ratios and other indicators to assess potential impacts on groundwater quality from septic systems: A review and examples from principal aquifers in the United States
Quality of Source Water from Public-Supply Wells in the United States, 1993-2007
The quality of our Nation’s waters: Quality of water from public-supply wells in the United States, 1993–2007: Overview of major findings
Depth-dependent sampling to identify short-circuit pathways to public-supply wells in multiple aquifer settings in the United States
Assessing the vulnerability of public-supply wells to contamination: Glacial aquifer system in Woodbury, Connecticut
Assessing the vulnerability of public-supply wells to contamination: Floridan aquifer system near Tampa, Florida
Assessing the Vulnerability of Public-Supply Wells to Contamination: Central Valley Aquifer System near Modesto, California
An Excel Workbook for Identifying Redox Processes in Ground Water
Assessing the vulnerability of public-supply wells to contamination—High Plains Aquifer near York, Nebraska
Simulated response of water quality in public supply wells to land use change
- 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.
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.
-
- 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... - Publications
Access publication on groundwater vulnerability to contamination below. For more publications on groundwater quality, search the USGS Publications Warehouse. Look here for help using the Pubs Warehouse.
The quality of our Nation's waters: factors affecting public-supply-well vulnerability to contamination: understanding observed water quality and anticipating future water quality
As part of the U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program, a study was conducted from 2001 to 2011 to shed light on factors that affect the vulnerability of water from public-supply wells to contamination (referred to hereafter as “public-supply-well vulnerability”). The study was designed as a follow-up to earlier NAWQA studies that found mixtures of contaminants atAuthorsSandra M. Eberts, Mary Ann Thomas, Martha L. JaguckiFilter Total Items: 34Using Cl/Br ratios and other indicators to assess potential impacts on groundwater quality from septic systems: A review and examples from principal aquifers in the United States
A detailed review was made of chemical indicators used to identify impacts from septic tanks on groundwater quality. Potential impacts from septic tank leachate on groundwater quality were assessed using the mass ratio of chloride–bromide (Cl/Br), concentrations of selected chemical constituents, and ancillary information (land use, census data, well depth, soil characteristics) for wells in princAuthorsB. G. Katz, S. M. Eberts, L. J. KauffmanQuality of Source Water from Public-Supply Wells in the United States, 1993-2007
More than one-third of the Nation's population receives their drinking water from public water systems that use groundwater as their source. The U.S. Geological Survey (USGS) sampled untreated source water from 932 public-supply wells, hereafter referred to as public wells, as part of multiple groundwater assessments conducted across the Nation during 1993-2007. The objectives of this study were tAuthorsPatricia L. Toccalino, Julia E. Norman, Kerie J. HittThe quality of our Nation’s waters: Quality of water from public-supply wells in the United States, 1993–2007: Overview of major findings
Summary of Major Findings and Implications About 105 million people in the United States-more than one-third of the Nation's population-receive their drinking water from about 140,000 public water systems that use groundwater as their source. Although the quality of finished drinking water (after treatment and before distribution) from these public water systems is regulated by the U.S. EnvironmeAuthorsPatricia L. Toccalino, Jessica A. HoppleDepth-dependent sampling to identify short-circuit pathways to public-supply wells in multiple aquifer settings in the United States
Depth-dependent water-quality and borehole flow data were used to determine where and how contamination enters public-supply wells (PSWs) at study sites in different principal aquifers of the United States. At each of three study sites, depth-dependent samples and wellbore flow data were collected from multiple depths in selected PSWs under pumping conditions. The chemistry of these depth-dependenAuthorsMatthew K. Landon, Bryant C. Jurgens, Brian G. Katz, Sandra M. Eberts, Karen R. Burow, Christy A. CrandallAssessing the vulnerability of public-supply wells to contamination: Glacial aquifer system in Woodbury, Connecticut
This fact sheet highlights findings from the vulnerability study of a public-supply well in Woodbury, Connecticut. The well typically produces water at the rate of 72 gallons per minute from the glacial aquifer system in the Pomperaug River Basin. Water samples were collected at the public-supply well and at monitoring wells installed in or near the simulated zone of contribution to the supply welAuthorsMartha L. Jagucki, Craig J. Brown, J. Jeffrey Starn, Sandra M. EbertsAssessing the vulnerability of public-supply wells to contamination: Floridan aquifer system near Tampa, Florida
This fact sheet highlights findings from the vulnerability study of a public-supply well in Temple Terrace, Florida, northeast of Tampa. The well selected for study typically produces water at the rate of 700 gallons per minute from the Upper Floridan aquifer. Water samples were collected at the public-supply well and at monitoring wells installed in or near the simulated zone of contribution to tAuthorsMartha L. Jagucki, Brian G. Katz, Christy A. Crandall, Sandra M. EbertsAssessing the Vulnerability of Public-Supply Wells to Contamination: Central Valley Aquifer System near Modesto, California
This fact sheet highlights findings from the vulnerability study of a public-supply well in Modesto, California. The well selected for study pumps on average about 1,600 gallons per minute from the Central Valley aquifer system during peak summer demand. Water samples were collected at the public-supply well and at monitoring wells installed in the Modesto vicinity. Samples from the public-supplyAuthorsMartha L. Jagucki, Bryant C. Jurgens, Karen R. Burow, Sandra M. EbertsAn Excel Workbook for Identifying Redox Processes in Ground Water
The reduction/oxidation (redox) condition of ground water affects the concentration, transport, and fate of many anthropogenic and natural contaminants. The redox state of a ground-water sample is defined by the dominant type of reduction/oxidation reaction, or redox process, occurring in the sample, as inferred from water-quality data. However, because of the difficulty in defining and applying aAuthorsBryant C. Jurgens, Peter B. McMahon, Francis H. Chapelle, Sandra M. EbertsAssessing the vulnerability of public-supply wells to contamination—High Plains Aquifer near York, Nebraska
The U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program found, in studies from 1991 to 2001, low levels of mixtures of contaminants in ground water near the water table in urban areas across the Nation. Although contaminants were detected less frequently in deeper ground water typically developed for public supply the proximity of contaminant mixtures to underlying public-waAuthorsMartha L. Jagucki, Matthew K. Landon, Brian R. Clark, Sandra M. EbertsSimulated response of water quality in public supply wells to land use change
Understanding how changes in land use affect water quality of public supply wells (PSW) is important because of the strong influence of land use on water quality, the rapid pace at which changes in land use are occurring in some parts of the world, and the large contribution of groundwater to the global water supply. In this study, groundwater flow models incorporating particle tracking and reactiAuthorsP. B. McMahon, K.R. Burow, L. J. Kauffman, S. M. Eberts, J.K. Böhlke, J.J. Gurdak