Volatile Organic Compounds (VOCs) Active
VOCs—Vapors in the Air, Dissolved in Groundwater
From dry-cleaning fluid to gasoline compounds to paint thinners, VOCs are common contaminants in groundwater
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
Learn more about VOCs in groundwater from the publications below.
Volatile organic compounds in the nation's ground water and drinking-water supply wells
Occurrence and implications of methyl tert-butyl ether and gasoline hydrocarbons in ground water and source water in the United States and in drinking water in 12 Northeast and Mid-Atlantic States, 1993-2002
Evaluation of volatilization as a natural attenuation pathway for MTBE
Occurrence of Methyl tert-Butyl Ether (MTBE) in public and private wells, Rockingham County, New Hampshire
LakeVOC; A Deterministic Model to Estimate Volatile Organic Compound Concentrations in Reservoirs and Lakes
Occurrence and temporal variability of methyl tert-butyl ether (MTBE) and other volatile organic compounds in select sources of drinking water : results of the focused survey
Volatile fuel hydrocarbons and MTBE in the environment
Effect of hydrologic and geochemical conditions on oxygen-enhanced bioremediation in a gasoline-contaminated aquifer
Seasonal and daily variations in concentrations of methyl-tertiary-butyl ether (MTBE) at Cranberry Lake, New Jersey
MTBE concentrations in ground water in Pennsylvania
Effects of daily precipitation and evapotranspiration patterns on flow and VOC transport to groundwater along a watershed flow path
Used motor oil as a source of MTBE, TAME, and BTEX to ground water
Methyl tert-butyl ether in ground and surface water of the United States: National-scale relations between MTBE occurrence in surface and ground water and MTBE use in gasoline
- 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
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. - 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: 39Occurrence and implications of methyl tert-butyl ether and gasoline hydrocarbons in ground water and source water in the United States and in drinking water in 12 Northeast and Mid-Atlantic States, 1993-2002
The occurrence and implications of methyl tert-butyl ether (MTBE) and gasoline hydrocarbons were examined in three surveys of water quality conducted by the U.S. Geological Survey?one national-scale survey of ground water, one national-scale survey of source water from ground water, and one regional-scale survey of drinking water from ground water. The overall detection frequency of MTBE in all thAuthorsMichael J. Moran, John S. Zogorski, Paul J. SquillaceEvaluation of volatilization as a natural attenuation pathway for MTBE
Volatilization and diffusion through the unsaturated zone can be an important pathway for natural attenuation remediation of methyl tert-butyl ether (MTBE) at gasoline spill sites. The significance of this pathway depends primarily on the distribution of immiscible product within the unsaturated zone and the relative magnitude of aqueous-phase advection (ground water recharge) to gaseous-phase difAuthorsMatthew A. Lahvis, Arthur L. Baehr, Ronald J. BakerOccurrence of Methyl tert-Butyl Ether (MTBE) in public and private wells, Rockingham County, New Hampshire
No abstract available.AuthorsJoseph D. Ayotte, Brian R. Mrazik, Denise M. Argue, Frederick J. McGarryLakeVOC; A Deterministic Model to Estimate Volatile Organic Compound Concentrations in Reservoirs and Lakes
This report documents LakeVOC, a model to estimate volatile organic compound (VOC) concentrations in lakes and reservoirs. LakeVOC represents the lake or reservoir as a two-layer system and estimates VOC concentrations in both the epilimnion and hypolimnion. The air-water flux of a VOC is characterized in LakeVOC in terms of the two-film model of air-water exchange. LakeVOC solves the system of coAuthorsDavid A. Bender, William E. Asher, John S. ZogorskiOccurrence and temporal variability of methyl tert-butyl ether (MTBE) and other volatile organic compounds in select sources of drinking water : results of the focused survey
The large-scale use of the gasoline oxygenate methyl tert-butyl ether (MTBE), and its high solubility, low soil adsorption, and low biodegradability, has resulted in its detection in ground water and surface water in many places throughout the United States. Studies by numerous researchers, as well as many State and local environmental agencies, have discovered high levels of MTBE in soils and groAuthorsGregory C. Delzer, Tamara IvahnenkoVolatile fuel hydrocarbons and MTBE in the environment
No abstract available.AuthorsIsabelle M. Cozzarelli, A. L. BaehrEffect of hydrologic and geochemical conditions on oxygen-enhanced bioremediation in a gasoline-contaminated aquifer
The effect of pre-existing factors, e.g., hydrologic, geochemical, and microbiological properties, on the results of oxygen addition to a reformulated gasoline-contaminated groundwater system was studied. Oxygen addition with an oxygen-release compound (a proprietary form of magnesium peroxide produced different results with respect to dissolved oxygen (DO) generation and contaminant decrease in tAuthorsJ. E. Landmeyer, P. M. BradleySeasonal and daily variations in concentrations of methyl-tertiary-butyl ether (MTBE) at Cranberry Lake, New Jersey
Methyl-tertiary-butyl ether (MTBE), an additive used to oxygenate gasoline, has been detected in lakes in northwestern New Jersey. This occurrence has been attributed to the use of gasoline-powered watercraft. This paper documents and explains both seasonal and daily variations in MTBE concentrations at Cranberry Lake. During a recent boating season (late April to September 1999), concentrations oAuthorsL. Toran, C. Lipka, A. Baehr, T. Reilly, R. BakerMTBE concentrations in ground water in Pennsylvania
The distribution, concentrations, and detection frequency of methyl tert-butyl-ether (MTBE), a gasoline additive used in reformulated gasoline to improve air quality, were characterized in Pennsylvania's ground water. Two sources of MTBE in ground water, the atmosphere and storage-tank release sites, were examined. An analysis of atmospheric MTBE concentrations shows that MTBE detections (MTBE greAuthorsSteven D. McAuleyEffects of daily precipitation and evapotranspiration patterns on flow and VOC transport to groundwater along a watershed flow path
MTBE and other volatile organic compounds (VOCs) are widely observed in shallow groundwater in the United States, especially in urban areas. Previous studies suggest that the atmosphere and/or nonpoint surficial sources could be responsible for some of those VOCs, especially in areas where there is net recharge to groundwater. However, in semi-arid locations where annual potential evapotranspiratiAuthorsRichard L. Johnson, R.B. Thoms, J.S. ZogorskiUsed motor oil as a source of MTBE, TAME, and BTEX to ground water
Methyl tert-butyl ether (MTBE), the widely used gasoline oxygenate, has been identified as a common ground water contaminant, and BTEX compounds (benzene, toluene, ethylbenzene, and xylenes) have long been associated with gasoline spills. Because not all instances of ground water contamination by MTBE and BTEX can be attributed to spills or leaking storage tanks, other potential sources need to beAuthorsR.J. Baker, E.W. Best, A. L. BaehrMethyl tert-butyl ether in ground and surface water of the United States: National-scale relations between MTBE occurrence in surface and ground water and MTBE use in gasoline
The detection frequency of methyl tert-butyl ether (MTBE) in ground and surface water of the United States is positively related to the content of MTBE in gasoline in various metropolitan areas of the U.S. The frequency of detection of MTBE is generally higher in areas that use larger amounts of MTBE in gasoline. Sampling of surface and ground water by the U.S. Geological Survey's National Water-QAuthorsMichael J. Moran, Rick M. Clawges, John S. Zogorski