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.
Have you ever pumped gas, had your clothes dry cleaned, or used chlorine bleach in your laundry or for disinfection? Then you’re likely to have encountered VOCs. Thousands of VOCs have been manufactured for use—many of these chemicals are toxic and can pose human-health or ecological concerns in drinking water or in the environment.
Although VOCs tend to escape from surface water through volatilization (evaporation) into the air, once dissolved in groundwater they are more persistent. They can be transported through the unsaturated zone in recharge, in soil vapor, or as a non-aqueous-phase liquid. Once in the saturated zone, some highly soluble VOCs, such as the gasoline additive MTBE, move with the groundwater, whereas other VOCs, like carbon tetrachloride, are slowed when they adhere to organic carbon in the aquifer solids. Some VOCs are degraded by bacteria in the aquifer, but others resist degradation and can be transported very long distances, in some cases reaching drinking-water supply wells.
Examples of VOCs
VOCs have been used extensively in the United States since the 1940s. VOCs are common components or additives in many commercial and household products, including gasoline, diesel fuel, other petroleum-based products, carpets, paints, varnishes, glues, spot removers, and cleaners. Industrial uses include the manufacturing of automobiles, electronics, computers, wood products, adhesives, dyes, rubber products, and plastics, and VOCs are used in the synthesis of other organic compounds. VOCs also are used in dry cleaning, in refrigeration units, and in the degreasing of equipment and home septic systems. VOCs are present in some personal care products such as perfumes, deodorants, insect repellents, skin lotions, and pharmaceuticals. Some VOCs also have been applied as fumigants in agriculture and in households to control insects, worms, and other pests.
VOCs in Groundwater
VOCs were analyzed in about 3,500 water samples collected during 1985–2001 from various types of wells, representing almost 100 different aquifer studies across the U.S. The group of VOCs most frequently detected in groundwater was trihalomethanes (THMs)—and of the THMs, chloroform was the most commonly detected. THMs form when chlorine interacts with dissolved organic matter in water, which can happen when chlorine is added to drinking water for disinfection of bacteria. Because some of that chlorinated drinking water goes down the drain, THMs are often detected in wastewater.
Solvents—with consumer and industrial uses such as degreasers, paint removers, and cleaning agents—also are among the VOCs detected in groundwater. Some solvents, like chloromethane, are no longer used in consumer products, but continue to be detected in groundwater if that contaminated groundwater recharged the aquifer back when the contaminant was still in use (see Groundwater Age).
Gasoline compounds and additives are another class of VOCs that is sometimes detected in groundwater. Leaking underground gasoline storage tanks are a common, but unseen, source of gasoline VOCs to groundwater.
MTBE—A VOC With a Groundwater History
Methyl tert-butyl ether (MtBE) in groundwater illustrates the law of unintended consequences. When lead was removed from gasoline in 1979, MtBE was sometimes used as a replacement to boost octane. In the 1990s, when federal laws required that the oxygenate content of gasoline be increased to reduce air pollution, MtBE was the most popular oxygenate added. MtBE quickly became a national issue in the United States in the 1990s because of its frequent detection in groundwater—MtBE dissolves readily in water, sorbs only weakly to soils, and, once in groundwater, resists degradation by bacteria.
Although not classified as a human carcinogen, neurological effects related to MtBE have been reported in humans, and kidney and liver tumors associated with MtBE have been reported in laboratory animals. Many states reacted to the frequent detection of MtBE in public supply wells by placing partial or complete bans on MtBE. In 2005, Congress removed the oxygen requirement from gasoline, and MtBE use in gasoline declined to negligible levels by 2007.
By 2012, MtBE concentrations were starting to decrease in some groundwater wells, but were unchanged in others, and still increasing in a few. This apparent contradiction reflects the complex mixture of groundwater ages in wells. Wells with mostly young groundwater are the most likely to have decreasing concentrations of MtBE in response to ending use of the gasoline additive. Wells with older groundwater and a broad mix of groundwater ages are the most likely to have concentrations of MtBE that are unchanging or even still increasing, as groundwater recharge carrying MtBE continues to slowly make its way to the well.
Follow the links below to learn more about topics related to VOCs and to groundwater quality.
Groundwater Age
Groundwater Quality Research
Groundwater/Surface-Water Interaction
Public Supply Wells
Domestic (Private) Supply Wells
Water-Quality Benchmarks for Contaminants
Groundwater Quality in Principal Aquifers of the Nation, 1991–2010
Groundwater Quality—Current Conditions and Changes Through Time
Rapid Fluctuations in Groundwater Quality
Predicting Groundwater Quality in Unmonitored Areas
Factors Affecting Vulnerability of Public-Supply Wells to Contamination
Learn more about VOCs in groundwater from the publications below.
Volatile organic compounds in the nation's ground water and drinking-water supply wells
Using groundwater age distributions to understand changes in methyl tert-butyl ether (MtBE) concentrations in ambient groundwater, northeastern United States
Trends in methyl tert-butyl ether concentrations in private wells in southeast New Hampshire: 2005 to 2015
The atmosphere can be a source of certain water soluble volatile organic compounds in urban streams
Design and evaluation of a field study on the contamination of selected volatile organic compounds and wastewater-indicator compounds in blanks and groundwater samples
Relative vulnerability of public supply wells to VOC contamination in hydrologically distinct regional aquifers
Methyl tert-butyl ether (MTBE) in public and private wells in New Hampshire: Occurrence, factors, and possible implications
Occurrence of MTBE and other gasoline oxygenates in CWS source waters
Source apportionment modeling of volatile organic compounds in streams
Effect of H2 and redox condition on biotic and abiotic MTBE transformation
Low-temperature MTBE biodegradation in aquifer sediments with a history of low, seasonal ground water temperatures
Methyl tert-butyl ether occurrence and related factors in public and private wells in southeast New Hampshire
Distribution of methyl tert-butyl ether (MTBE) and selected water-quality constituents in the surficial aquifer at the Dover National Test Site, Dover Air Force Base, Delaware, 2001
- Overview
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.
Have you ever pumped gas, had your clothes dry cleaned, or used chlorine bleach in your laundry or for disinfection? Then you’re likely to have encountered VOCs. Thousands of VOCs have been manufactured for use—many of these chemicals are toxic and can pose human-health or ecological concerns in drinking water or in the environment.
Although VOCs tend to escape from surface water through volatilization (evaporation) into the air, once dissolved in groundwater they are more persistent. They can be transported through the unsaturated zone in recharge, in soil vapor, or as a non-aqueous-phase liquid. Once in the saturated zone, some highly soluble VOCs, such as the gasoline additive MTBE, move with the groundwater, whereas other VOCs, like carbon tetrachloride, are slowed when they adhere to organic carbon in the aquifer solids. Some VOCs are degraded by bacteria in the aquifer, but others resist degradation and can be transported very long distances, in some cases reaching drinking-water supply wells.
Examples of VOCs
USGS technicians collecting groundwater samples for analysis of water quality, including VOCs. (Credit: Alan Cressler.) VOCs have been used extensively in the United States since the 1940s. VOCs are common components or additives in many commercial and household products, including gasoline, diesel fuel, other petroleum-based products, carpets, paints, varnishes, glues, spot removers, and cleaners. Industrial uses include the manufacturing of automobiles, electronics, computers, wood products, adhesives, dyes, rubber products, and plastics, and VOCs are used in the synthesis of other organic compounds. VOCs also are used in dry cleaning, in refrigeration units, and in the degreasing of equipment and home septic systems. VOCs are present in some personal care products such as perfumes, deodorants, insect repellents, skin lotions, and pharmaceuticals. Some VOCs also have been applied as fumigants in agriculture and in households to control insects, worms, and other pests.
VOCs in Groundwater
VOCs were analyzed in about 3,500 water samples collected during 1985–2001 from various types of wells, representing almost 100 different aquifer studies across the U.S. The group of VOCs most frequently detected in groundwater was trihalomethanes (THMs)—and of the THMs, chloroform was the most commonly detected. THMs form when chlorine interacts with dissolved organic matter in water, which can happen when chlorine is added to drinking water for disinfection of bacteria. Because some of that chlorinated drinking water goes down the drain, THMs are often detected in wastewater.
Solvents—with consumer and industrial uses such as degreasers, paint removers, and cleaning agents—also are among the VOCs detected in groundwater. Some solvents, like chloromethane, are no longer used in consumer products, but continue to be detected in groundwater if that contaminated groundwater recharged the aquifer back when the contaminant was still in use (see Groundwater Age).
Gasoline compounds and additives are another class of VOCs that is sometimes detected in groundwater. Leaking underground gasoline storage tanks are a common, but unseen, source of gasoline VOCs to groundwater.
MTBE—A VOC With a Groundwater History
Methyl tert-butyl ether (MtBE) in groundwater illustrates the law of unintended consequences. When lead was removed from gasoline in 1979, MtBE was sometimes used as a replacement to boost octane. In the 1990s, when federal laws required that the oxygenate content of gasoline be increased to reduce air pollution, MtBE was the most popular oxygenate added. MtBE quickly became a national issue in the United States in the 1990s because of its frequent detection in groundwater—MtBE dissolves readily in water, sorbs only weakly to soils, and, once in groundwater, resists degradation by bacteria.
Although not classified as a human carcinogen, neurological effects related to MtBE have been reported in humans, and kidney and liver tumors associated with MtBE have been reported in laboratory animals. Many states reacted to the frequent detection of MtBE in public supply wells by placing partial or complete bans on MtBE. In 2005, Congress removed the oxygen requirement from gasoline, and MtBE use in gasoline declined to negligible levels by 2007.
By 2012, MtBE concentrations were starting to decrease in some groundwater wells, but were unchanged in others, and still increasing in a few. This apparent contradiction reflects the complex mixture of groundwater ages in wells. Wells with mostly young groundwater are the most likely to have decreasing concentrations of MtBE in response to ending use of the gasoline additive. Wells with older groundwater and a broad mix of groundwater ages are the most likely to have concentrations of MtBE that are unchanging or even still increasing, as groundwater recharge carrying MtBE continues to slowly make its way to the well.
- Science
Follow the links below to learn more about topics related to VOCs and to groundwater quality.
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.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...Water-Quality Benchmarks for Contaminants
How does the water quality measure up? It all depends on what the water will be used for and what contaminants are of interest. Water-quality benchmarks are designed to protect drinking water, recreation, aquatic life, and wildlife. Here you’ll find links to some of the most widely used sets of water, sediment, and fish tissue benchmarks and general guidance about their interpretation.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.Groundwater Quality—Current Conditions and Changes Through 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.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.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... - Publications
Learn more about VOCs in groundwater from the publications below.
Volatile organic compounds in the nation's ground water and drinking-water supply wells
This national assessment of 55 volatile organic compounds (VOCs) in ground water gives emphasis to the occurrence of VOCs in aquifers that are used as an important supply of drinking water. In contrast to the monitoring of VOC contamination of ground water at point-source release sites, such as landfills and leaking underground storage tanks (LUSTs), our investigations of aquifers are designed asAuthorsJohn S. Zogorski, Janet M. Carter, Tamara Ivahnenko, Wayne W. Lapham, Michael J. Moran, Barbara L. Rowe, Paul J. Squillace, Patricia L. ToccalinoFilter Total Items: 39Using 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. DeSimoneTrends in methyl tert-butyl ether concentrations in private wells in southeast New Hampshire: 2005 to 2015
In southeast New Hampshire, where reformulated gasoline was used from the 1990s to 2007, methyl tert-butyl ether (MtBE) concentrations ≥0.2 μg/L were found in water from 26.7% of 195 domestic wells sampled in 2005. Ten years later in 2015, and eight years after MtBE was banned, 10.3% continue to have MtBE. Most wells (140 of 195) had no MtBE detections (concentrations <0.2 μg/L) in 2005 and 2015.AuthorsSarah Flanagan, Joseph P. Levitt, Joseph D. AyotteThe atmosphere can be a source of certain water soluble volatile organic compounds in urban streams
Surface water and air volatile organic compound (VOC) data from 10 U.S. Geological Survey monitoring sites were used to evaluate the potential for direct transport of VOCs from the atmosphere to urban streams. Analytical results of 87 VOC compounds were screened by evaluating the occurrence and detection levels in both water and air, and equilibrium concentrations in water (Cws) based on the measuAuthorsScott J. Kenner, David A. Bender, John S. Zogorski, James F. PankowDesign and evaluation of a field study on the contamination of selected volatile organic compounds and wastewater-indicator compounds in blanks and groundwater samples
The Field Contamination Study (FCS) was designed to determine the field processes that tend to result in clean field blanks and to identify potential sources of contamination to blanks collected in the field from selected volatile organic compounds (VOCs) and wastewater-indicator compounds (WICs). The VOCs and WICs analyzed in the FCS were detected in blanks collected by the U.S. Geological SurveyAuthorsSusan A. Thiros, David A. Bender, David K. Mueller, Donna L. Rose, Lisa D. Olsen, Jeffrey D. Martin, Bruce Bernard, John S. ZogorskiRelative vulnerability of public supply wells to VOC contamination in hydrologically distinct regional aquifers
A process-based methodology was used to compare the vulnerability of public supply wells tapping seven study areas in four hydrologically distinct regional aquifers to volatile organic compound (VOC) contamination. This method considers (1) contributing areas and travel times of groundwater flowpaths converging at individual supply wells, (2) the oxic and/or anoxic conditions encountered along eacAuthorsLeon J. Kauffman, Francis H. ChapelleMethyl tert-butyl ether (MTBE) in public and private wells in New Hampshire: Occurrence, factors, and possible implications
Methyl tert-butyl ether (MTBE) concentrations ???0.2 ??g/L were found in samples of untreated water in 18% of public-supply wells (n = 284) and 9.1% of private domestic wells (n = 264) sampled in 2005 and 2006 in New Hampshire. In counties that used reformulated gasoline (RFG), MTBE occurred at or above 0.2 ??g/L in 30% of public- and 17% of private-supply wells. Additionally, 52% of public-supplyAuthorsJ. D. Ayotte, D.M. Argue, F.J. McGarry, J.R. Degnan, L. Hayes, S. M. Flanagan, D.R. HelselOccurrence of MTBE and other gasoline oxygenates in CWS source waters
Results from two national surveys indicate that the gasoline oxygenate methyl tertiary butyl ether (MTBE) is one of the most frequently detected volatile organic compounds in source waters used by community water systems in the United States. Three other ether oxygenates were detected infrequently but almost always co-occurred with MTBE. A random sampling of source waters across the United StatesAuthorsJanet M. Carter, Stephen J. Grady, Gregory C. Delzer, Bart Koch, John S. ZogorskiSource apportionment modeling of volatile organic compounds in streams
It often is of interest to understand the relative importance of the different sources contributing to the concentration cw of a contaminant in a stream; the portions related to sources 1, 2, 3, etc. are denoted cw,1, cw,2, cw,3, etc. Like c w, 'he fractions ??1, = cw,1/c w, ??2 = cw,2/cw, ??3 = cw,3/cw, etc. depend on location and time. Volatile organic compounds (VOCs) can undergo absorption froAuthorsJ. F. Pankow, W.E. Asher, J.S. ZogorskiEffect of H2 and redox condition on biotic and abiotic MTBE transformation
Laboratory studies conducted with surface water sediment from a methyl tert-butyl ether (MTBE)-contaminated site in South Carolina demonstrated that, under methanogenic conditions, [U-14C] MTBE was transformed to 14C tert-butyl alcohol (TBA) with no measurable production of 14CO2. Production of TBA was not attributed to the activity of methanogenic microorganisms, however, because comparable transAuthorsP. M. Bradley, F. H. Chapelle, J. E. LandmeyerLow-temperature MTBE biodegradation in aquifer sediments with a history of low, seasonal ground water temperatures
Sediments from two shallow, methyl tert‐butyl ether (MTBE)–contaminated aquifers, with mean ground water temperatures ∼10°C, demonstrated significant mineralization of [U‐14C] MTBE to 14CO2 at incubation temperatures as low as 4°C. These results indicate that microbial degradation can continue to contribute to the attenuation of MTBE in ground water under wintertime, low‐temperature conditions.AuthorsP. M. Bradley, J. E. LandmeyerMethyl tert-butyl ether occurrence and related factors in public and private wells in southeast New Hampshire
The occurrence of methyl tert-butyl ether (MTBE) in water from public wells in New Hampshire has increased steadily over the past several years. Using a laboratory reporting level of 0.2 μg/L, 40% of samples from public wells and 21% from private wells in southeast New Hampshire have measurable concentrations of MTBE. The rate of occurrence of MTBE varied significantly for public wells by establisAuthorsJoseph D. Ayotte, Denise M. Argue, Frederick J. McGarryDistribution of methyl tert-butyl ether (MTBE) and selected water-quality constituents in the surficial aquifer at the Dover National Test Site, Dover Air Force Base, Delaware, 2001
A joint study by the Dover National Test Site, Dover Air Force Base, Delaware, and the U.S. Geological Survey was conducted from June 27 through July 18, 2001, to determine the spatial distribution of the gasoline oxygenate additive methyl tert-butyl ether and selected water-quality constituents in the surficial aquifer underlying the Dover National Test Site. This report provides a summary assessAuthorsMarie Stewart, William R. Guertal, Jeffrey R. Barbaro, Timothy J. McHale