Mar 29, 2021

USGS Study Finds Drought May Lead to Elevated Levels of Arsenic in Private Domestic Wells

According to the study, an estimated 4.1 million people in the lower 48 states are potentially exposed to arsenic levels that exceed EPA’s drinking water standards.


well water

A U.S. Geological Survey (USGS) study showed that drought may lead to elevated levels of naturally occurring arsenic and that the longer a drought lasts the higher the probability of arsenic concentrations exceeding U.S. EPA drinking water standards. 

Although the study indicates that drought may increase the likelihood of having high concentrations of arsenic in domestic wells, it does not indicate how drought may impact arsenic concentrations at individual wells. 

“The occurrence of arsenic in groundwater is complex and dependent on many local geochemical mechanisms, interactions, and hydrologic flow paths,” stated the study about its limitations and implications. 

This private well water study is the first of its kind on a national-scale, according to USGS. The study was conducted in collaboration with the CDC. 

According to researcher estimates, during drought conditions, 4.1 million people in the lower 48 states who use private domestic wells are likely exposed to unsafe levels of arsenic, reported the study. This is an increase of 54% from an estimated 2.7 million people exposed to unhealthy arsenic levels in private wells during non-drought conditions. 

“The population potentially exposed to arsenic levels exceeding the EPA standard during simulated drought conditions amounts to roughly one-tenth of the estimated 37.2 to 43.2 million people in the conterminous U.S. who use domestic wells for household water supply,” said Melissa Lombard, a USGS hydrologist and lead author of this study, reported USGS.

The study used an existing USGS statistical model that predicts the probability for elevated arsenic concentrations in domestic well water. Scientists used the model to simulate drought conditions by changing precipitation and groundwater levels and the researchers also used data from the drought of 2012 to investigate how drought duration can impact arsenic levels.

The study did not examine private domestic wells in Alaska or Hawaii and includes maps showing where simulated drought conditions are likely to increase the probability of high arsenic levels and the number of people potentially exposed. 

According to USGS, the states with the largest populations facing elevated arsenic levels in private domestic well water during the simulated drought conditions are Ohio (approximately 374,000 people), Michigan (320,000 people), Indiana (267,000 people), Texas (200,000 people) and California (196,000 people).

Under normal conditions, the largest populations potentially exposed to high levels of arsenic are in Ohio (approximately 241,000 people), Michigan (226,000 people), Indiana (162,000 people), California (157,000 people) and Maine (121,000 people), according to the study.

The study, “Assessing the Impact of Drought on Arsenic Exposure from Private Domestic Wells in the Conterminous United States,” is published in Environmental Science and Technology and available here.

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