5 States with High Levels of Arsenic in Groundwater

May 9, 2018
5 States with High Levels of Arsenic in Groundwater
Estimated population with arsenic greater than 10 micrograms per liter

Arsenic is a chemical element that enters the environment from mineral deposits, industrial activity, pesticides and the smelting of metals. In high levels, arsenic can cause toxicity, liver and kidney damage, and even cancer. In 2001, the U.S. Environmental Protection Agency (EPA) set a maximum contaminant level of 10 ppb for arsenic in all potable water.

Since the standard went into effect in 2006, however, some states have had trouble with compliance because their groundwater has high arsenic concentrations. A study by the U.S. Geological Survey reports that an estimated 2.1 million people across the United States may be drinking water from wells that have arsenic concentrations above the EPA limit (shown in the map above). This is true for many areas in the following 5 states:

1. California. Arsenic is commonly found in California’s groundwater, primarily due to natural sources. According to data from the State Water Resources Control Board Division of Water Quality GAMA Program, Kern, Los Angeles and San Bernardino counties have the most active and standby public water wells with arsenic concentrations above 10 ppb in the state. Additionally, nearly 10% of all water wells tested in the GAMA Program’s study had high arsenic concentrations.

2. Nevada. Arsenic is also one of the most common contaminants found in Nevada’s well water. Arsenic enters groundwater through natural mineral deposits and mining activities, as well as from petroleum refining, wood preservatives and herbicides.

3. Arizona. The Arizona Department of Health Services maintains that arsenic is present in almost all of the state’s groundwater. Because the majority of residents in rural parts of Arizona get their drinking water from unregulated, private water wells, the Office of Environmental Health recommends that water from all new drinking wells be tested prior to use for cooking or drinking to mitigate arsenic poisoning.

4. Illinois. Some parts of Illinois have minerals with naturally high levels of arsenic that deposit into groundwater. Prior to the enforcement of the 10 ppb EPA standard, 11% of the community water well water samples in the Illinois State Water Survey (ISWS) Water Quality Database had arsenic levels above 10 ppb. In addition, there were counties in which half of the groundwater samples from private wells had high arsenic concentrations. 

5. Maine. According to information from the Maine Center for Disease Control & Prevention, approximately 1 in 10 drilled wells in Maine have water with high levels of arsenic. Although water from drilled wells more commonly have high arsenic concentrations, water with high levels of arsenic can be found throughout the state—even in some dug wells. The state recommends that all household wells be tested for arsenic.


Arsenic levels maps –

  1. https://www.usgs.gov/news/study-estimates-about-21-million-people-using-wells-high-arsenic
  2. https://water.usgs.gov/nawqa/trace/pubs/geo_v46n11/fig3.html

Contaminants (causes and effects) –

  1.  https://water.usgs.gov/edu/groundwater-contaminants.html

California –

  1. https://www.waterboards.ca.gov/water_issues/programs/gama/docs/coc_arsenic.pdf

Nevada –

  1. https://ndep.nv.gov/uploads/water-labcert-dwtesting-docs/common_probs.pdf

Arizona –

  1. https://azdhs.gov/documents/preparedness/epidemiology-disease-control/environmental-toxicology/about-arsenic-groundwater.pdf

Illinois –

  1.  http://www.epa.state.il.us/water/groundwater/publications/arsenic/
  2. http://www.dph.illinois.gov/topics-services/environmental-health-protection/private-water/arsenic-groundwater
  3. http://www.dph.illinois.gov/topics-services/environmental-health-protection/private-water/arsenic-groundwater

Maine –

  1. https://www.maine.gov/dhhs/mecdc/public-health-systems/health-and-environmental-testing/arsenic.htm

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