Arsenic and Drinking Water Active
Arsenic Found in Groundwater
Study Estimates about 2.1 Million People using Wells High in Arsenic
Arsenic is a naturally occurring element, but long-term exposure can cause cancer in people. There has been a substantial amount of research done to address arsenic in groundwater and drinking-water supplies around the country. The USGS studies local and national sources of arsenic to help health officials better manage our water resources.
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.
BACKGROUND
Arsenic occurs naturally as a trace component in many rocks and sediments. Whether the arsenic is released from these geologic sources into groundwater depends on the chemical form of the arsenic, the geochemical conditions in the aquifer, and the biogeochemical processes that occur. Arsenic also can be released into groundwater as a result of human activities, such as mining, and from its various uses in industry, in animal feed, as a wood preservative, and as a pesticide. In drinking-water supplies, arsenic poses a problem because it is toxic at low levels and is a known carcinogen. In 2001, the USEPA lowered the MCL for arsenic in public-water supplies to 10 micrograms per liter (µg/L) from 50 µg/L.
DANGEROUS GROUNDWATER SUPPLIES
The USGS plays an active role in protecting human health from potential issues related to our Nation's natural resources. One vital aspect is assessing the water quality of groundwater supplies. Whether across the U.S. or around the world, the USGS helps measure and monitor drinking water supplies for contaminants like arsenic. For example, dangerously high levels of arsenic have been found in drinking water wells in more than 25 states in the United States, potentally exposing 2.1 million people1 to drinking water high in arsenic. Possibly the worst case ever of arsenic poisoning occurred in Bangladesh, where over 100 million people2 were poisoned by arsenic in groundwater supplies.
In a national study of groundwater quality, the USGS found that arsenic was detected in nearly half of the wells sampled in parts of aquifers used for drinking-water supply at a concentration of 1 µg/L or greater. Detections were more common and concentrations generally were higher in the west than in the east. About 7 percent of the wells sampled contained arsenic at a concentration that exceeded the MCL of 10 µg/L, indicating a potential health risk. The greatest concern was in the Southwest, where concentrations of arsenic exceeded the MCL in about 16 percent of drinking-water wells sampled. Other Principal Aquifers with concerns for arsenic included the Glacial aquifer system (northern U.S.), the crystalline rock aquifers of the Piedmont, Blue Ridge, and Valley and Ridge Aquifers (northern U.S.), and the Mississipppi Embayment–Texas Coastal Uplands Aquifer System and Mississippi River Valley Alluvial Aquifer (southeastern U.S.).
In the Southwest basin-fill aquifers, arsenic concentrations in drinking-water wells exceeded the MCL more than twice as frequently as in drinking-water wells nationwide. The source is the volcanic and granitic rocks through which that groundwater moves. [maybe use photo from p. 18] Factors that contribute to elevated concentrations of arsenic in these aquifers include long groundwater residence times, rock type, high pH, arid climate, and irrigation practices.
The USEPA estimated in 2001 that the annual cost to reduce arsenic concentrations to below the MCL would range from $0.86 to $32 per household for customers of large public water systems (more than 10,000 people) to $165 to $327 per household for very small systems (25–500 people). Understanding the factors that affect concentrations of arsenic and other contaminants with geologic sources in groundwater can help water suppliers prioritize areas for new groundwater development and reduce treatment costs.
RELATED USGS RESEARCH
The unique hydrogeologic character of this health hazard makes USGS research crucial for understanding this hazard and helping water-supply and public-health authorities implement strategies to mitigate this risk. The USGS investigates the presence and effect of arsenic in drinking water supplies, monitors the worldwide distribution of arsenic in groundwater, and assesses the impact of arsenic on local stream sediment chemistry.
- Groundwater Quality—Current Conditions and Changes Through Time
- Predicting Groundwater Quality in Unmonitored Areas
ADDITIONAL RESOURCES
- Drinking water requirements for arsenic (U.S. Environmental Protection Agency)
- In Small Doses: Arsenic (Dartmouth University)
- Arsenic (Agency for Toxic Substances and Disease Registry)
- Map of Arsenic concentrations in groundwater of the United States (DATA.GOV)
Below are data or web applications associated with research on arsenic and water quality.
Learn about the USGS research on arsenic in water used as a drinking resource.
Estimating the high-arsenic domestic-well population in the conterminous United States
Predicted nitrate and arsenic concentrations in basin-fill aquifers of the Southwestern United States
Assessment of arsenic concentrations in domestic well water, by town, in Maine 2005-09
The association of arsenic with redox conditions, depth, and ground-water age in the glacial aquifer system of the northern United States
Worldwide occurrences of arsenic in ground water
Arsenic in Ground-Water Resources of the United States
A Retrospective Analysis on the Occurrence of Arsenic in Ground-Water Resources of the United States and Limitations in Drinking-Water-Supply Characterizations
Stay informed of media alerts and news stories about when and where arsenic is being discovered in water supplies across the country.
Study Estimates about 2.1 Million People using Wells High in Arsenic
Most Arsenic Presumed to be From Naturally Occurring Sources
- Overview
Arsenic is a naturally occurring element, but long-term exposure can cause cancer in people. There has been a substantial amount of research done to address arsenic in groundwater and drinking-water supplies around the country. The USGS studies local and national sources of arsenic to help health officials better manage our water resources.
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.
BACKGROUND
Arsenic occurs naturally as a trace component in many rocks and sediments. Whether the arsenic is released from these geologic sources into groundwater depends on the chemical form of the arsenic, the geochemical conditions in the aquifer, and the biogeochemical processes that occur. Arsenic also can be released into groundwater as a result of human activities, such as mining, and from its various uses in industry, in animal feed, as a wood preservative, and as a pesticide. In drinking-water supplies, arsenic poses a problem because it is toxic at low levels and is a known carcinogen. In 2001, the USEPA lowered the MCL for arsenic in public-water supplies to 10 micrograms per liter (µg/L) from 50 µg/L.
DANGEROUS GROUNDWATER SUPPLIES
The USGS plays an active role in protecting human health from potential issues related to our Nation's natural resources. One vital aspect is assessing the water quality of groundwater supplies. Whether across the U.S. or around the world, the USGS helps measure and monitor drinking water supplies for contaminants like arsenic. For example, dangerously high levels of arsenic have been found in drinking water wells in more than 25 states in the United States, potentally exposing 2.1 million people1 to drinking water high in arsenic. Possibly the worst case ever of arsenic poisoning occurred in Bangladesh, where over 100 million people2 were poisoned by arsenic in groundwater supplies.
In a national study of groundwater quality, the USGS found that arsenic was detected in nearly half of the wells sampled in parts of aquifers used for drinking-water supply at a concentration of 1 µg/L or greater. Detections were more common and concentrations generally were higher in the west than in the east. About 7 percent of the wells sampled contained arsenic at a concentration that exceeded the MCL of 10 µg/L, indicating a potential health risk. The greatest concern was in the Southwest, where concentrations of arsenic exceeded the MCL in about 16 percent of drinking-water wells sampled. Other Principal Aquifers with concerns for arsenic included the Glacial aquifer system (northern U.S.), the crystalline rock aquifers of the Piedmont, Blue Ridge, and Valley and Ridge Aquifers (northern U.S.), and the Mississipppi Embayment–Texas Coastal Uplands Aquifer System and Mississippi River Valley Alluvial Aquifer (southeastern U.S.).
In the Southwest basin-fill aquifers, arsenic concentrations in drinking-water wells exceeded the MCL more than twice as frequently as in drinking-water wells nationwide. The source is the volcanic and granitic rocks through which that groundwater moves. [maybe use photo from p. 18] Factors that contribute to elevated concentrations of arsenic in these aquifers include long groundwater residence times, rock type, high pH, arid climate, and irrigation practices.
The USEPA estimated in 2001 that the annual cost to reduce arsenic concentrations to below the MCL would range from $0.86 to $32 per household for customers of large public water systems (more than 10,000 people) to $165 to $327 per household for very small systems (25–500 people). Understanding the factors that affect concentrations of arsenic and other contaminants with geologic sources in groundwater can help water suppliers prioritize areas for new groundwater development and reduce treatment costs.
RELATED USGS RESEARCH
The unique hydrogeologic character of this health hazard makes USGS research crucial for understanding this hazard and helping water-supply and public-health authorities implement strategies to mitigate this risk. The USGS investigates the presence and effect of arsenic in drinking water supplies, monitors the worldwide distribution of arsenic in groundwater, and assesses the impact of arsenic on local stream sediment chemistry.
- Groundwater Quality—Current Conditions and Changes Through Time
- Predicting Groundwater Quality in Unmonitored Areas
ADDITIONAL RESOURCES- Drinking water requirements for arsenic (U.S. Environmental Protection Agency)
- In Small Doses: Arsenic (Dartmouth University)
- Arsenic (Agency for Toxic Substances and Disease Registry)
- Map of Arsenic concentrations in groundwater of the United States (DATA.GOV)
- Science
- Data
Below are data or web applications associated with research on arsenic and water quality.
- Publications
Learn about the USGS research on arsenic in water used as a drinking resource.
Estimating 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. NolanFilter Total Items: 18Predicted nitrate and arsenic concentrations in basin-fill aquifers of the Southwestern United States
The National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey (USGS) is conducting a regional analysis of water quality in the principal aquifer systems across the United States. The Southwest Principal Aquifers (SWPA) study is building a better understanding of the susceptibility and vulnerability of basin-fill aquifers in the region to groundwater contamination by synthesizAuthorsDavid W. Anning, Angela P. Paul, Tim S. McKinney, Jena M. Huntington, Laura M. Bexfield, Susan A. ThirosAssessment of arsenic concentrations in domestic well water, by town, in Maine 2005-09
Prior studies have established that approximately 10 percent of domestic wells in Maine have arsenic levels greater than the U.S. Environmental Protection Agency maximum contaminant limit (10 micrograms per liter (ug/L)). Of even greater concern are multiple discoveries of wells with very high arsenic levels (> 500 ug/L) in several areas of the State. A study was initiated to assist the Maine CentAuthorsM.G. Nielsen, P.J. Lombard, L.F. SchalkThe association of arsenic with redox conditions, depth, and ground-water age in the glacial aquifer system of the northern United States
More than 800 wells in the glacial aquifer system of the Northern United States were sampled for arsenic as part of U.S. Geological Survey National Water-Quality Assessment (NAWQA) studies during 1991-2003. Elevated arsenic concentrations (greater than or equal to 10 micrograms per liter) were detected in 9 percent of samples. Elevated arsenic concentrations were associated with strongly reduciAuthorsMary Ann ThomasWorldwide occurrences of arsenic in ground water
Numerous aquifers worldwide carry soluble arsenic at concentrations greater than the World Health Organization--and U.S. Environmental Protection Agency--recommended drinking water standard of 10 mg per liter. Sources include both natural (black shales, young sediments with low flushing rates, gold mineralization, and geothermal environments) and anthropogenic (mining activities, livestock feed adAuthorsD. Kirk NordstromArsenic in Ground-Water Resources of the United States
Arsenic is a naturally occurring element in rocks, soils, and the waters in contact with them. Recognized as a toxic element for centuries, arsenic today also is a human health concern because it can contribute to skin, bladder, and other cancers (National Research Council, 1999). Recently, the National Research Council (1999) recommended lowering the current maximum contaminant level (MCL) alloweAuthorsAlan H. Welch, Sharon A. Watkins, Dennis R. Helsel, Michael J. FocazioA Retrospective Analysis on the Occurrence of Arsenic in Ground-Water Resources of the United States and Limitations in Drinking-Water-Supply Characterizations
The Safe Drinking Water Act, as amended in 1996, requires the U.S. Environmental Protection Agency (USEPA) to review current drinking-water standards for arsenic, propose a maximum contaminant level for arsenic by January 1, 2000, and issue a final regulation by January, 2001. Quantification of the national occurrence of targeted ranges in arsenic concentration in ground water used for public drinAuthorsMichael J. Focazio, Alan H. Welch, Sharon A. Watkins, Dennis R. Helsel, Marilee A. Horn - News
Stay informed of media alerts and news stories about when and where arsenic is being discovered in water supplies across the country.
Study Estimates about 2.1 Million People using Wells High in Arsenic
Most Arsenic Presumed to be From Naturally Occurring Sources