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.
Updated Information on U.S. Groundwater: Arsenic among many concerns
Three new fact sheets add to information on groundwater quality in the Nation's most heavily used aquifers. Arsenic is among the constituents that most frequently exceed human-health benchmarks.
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)
Drinking Water and Source Water Research
Metals and Other Trace Elements
Public Supply Wells
Domestic (Private) Supply Wells
Groundwater Quality in Principal Aquifers of the Nation, 1991–2010
Groundwater Quality—Current Conditions and Changes Through Time
Predicting Groundwater Quality in Unmonitored Areas
Groundwater Age
Oxidation/Reduction (Redox)
Study to Test a Novel Shallow Well Design that May Provide Contaminant-Free Water Supply to Domestic Well Users in Arsenic-Prone Parts of the United States
Towards Understanding the Impact of Drought on the Arsenic Hazard for the Private Domestic Well Population in the United States
Mapping and Characterizing the Arsenic Hazard in Private Well Water Across the Nation
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.
Updated Information on U.S. Groundwater: Arsenic among many concerns
Three new fact sheets add to information on groundwater quality in the Nation's most heavily used aquifers. Arsenic is among the constituents that most frequently exceed human-health benchmarks.
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.
This map shows estimates of how many private domestic well users in each county may be drinking water with levels of arsenic of possible concern for human health.(µg/L, micrograms per liter)
Sources/Usage: Public Domain. Visit Media to see details.Arsenic was detected more frequently and at higher concentrations in wells in the West than in the East. Symbols represent median concentration in networks of 20-30 wells. Figure from USGS Circular 1360, Water Quality in Principal Aquifers of the United States, 1991-2010. 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
Drinking Water and Source Water Research
Reliable drinking water is vital for the health and safety of all Americans. The USGS monitors and assesses the quality of the water used as a source for our nation's drinking water needs.Metals and Other Trace Elements
Metals, metalloids, and radionuclides all are trace elements that occur naturally in the Earth's crust. In small quantities many trace elements are essential for health in all living organisms, but some trace elements can be toxic or cause cancer, and some can bioaccumulate. The USGS investigates where and how trace elements make their way into our Nation's surface water and groundwater.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.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.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.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.Oxidation/Reduction (Redox)
The redox state of groundwater—whether the groundwater is oxic (oxidized) or anoxic (reduced)—has profound implications for groundwater quality. Knowing the redox conditions of groundwater can help determine whether it contains elevated levels of many contaminants, including arsenic, nitrate, and even some manmade contaminants.Study to Test a Novel Shallow Well Design that May Provide Contaminant-Free Water Supply to Domestic Well Users in Arsenic-Prone Parts of the United States
The USGS, the University of New Hampshire, U.S. Environmental Protection Agency, the New Hampshire Department of Environmental Services, and the Maine Geological Survey are collaborating on a study of a novel shallow well design that might be able to provide safe drinking water to domestic well users in arsenic-prone parts of the Nation.Towards Understanding the Impact of Drought on the Arsenic Hazard for the Private Domestic Well Population in the United States
The USGS and the Centers for Disease Control and Prevention are examining the potential effects of droughts on the arsenic hazard in private well water across the Nation.Mapping and Characterizing the Arsenic Hazard in Private Well Water Across the Nation
Study estimates about 2.1 million people using wells high in arsenic: USGS research directly supports federal agencies concerned with public health—specifically, understanding natural hazards in private domestic drinking water and the risk they pose to human health. - Data
- Publications
- 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