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Contaminants in Public Supply Wells

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Detailed Description

More than a third of the Nation receives drinking water from public wells. The USGS has released new information on contaminants in these wells. In this USGS podcast Kara Capelli talks to USGS Scientist Patricia Toccalino, who led the study on contaminants in these wells




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[Intro Music]

Kara: Welcome to USGS CoreCast Do you ever wonder how the people who run public water systems know which contaminants to look for and to treat? The U.S. Geological Survey has just completed a study on contaminants in ground water pumped from public wells. The study focus on the source water for the system or the water that hasn't been treated or blended. I'm here with Dr. Patricia Toccalino, a USGS Hydrologist and the lead scientist on the study.

Patty, thank you so much for being here.

Patricia Toccalino: Thanks, Kara, it's my pleasure.

Kara: So why is it important to study public wells?

Patricia Toccalino: Well, we study public wells because more than one-third of our nation's population receive their drinking water from public wells. Assessing the quality of our sources of drinking water is important because it provides a perspective on where contaminants come from, what levels of treatment may be needed for different sources of water, and what constraints there may be on development of ground water resources as future drinking water supplies.


Kara: Well, what exactly is source water?

Patricia Toccalino: Source water is the untreated water that enters the drinking water system before any treatment or blending that takes place. It's not the finished drinking water that water utilities deliver to their customers.

Kara: And why is it important to study the contaminants in source water before it's treated?

Patricia Toccalino: That's a great question. Finished drinking water is extensively monitored by drinking water utilities as part of the requirements of the Safe Drinking Water Act. And that's the national law safeguarding tap water in the United States. Our study complements this regulatory monitoring because we evaluated many contaminants that are not regulated in drinking water. We evaluated which contaminants or potential health concerns in our ground water resources, in which areas types of aquifers are most vulnerable to different types of contaminations.

Kara: So how often are contaminants in our sources of drinking water a potential health concern?


Patricia Toccalino: About one of every five wells that we sampled had at least one contaminant at a level of potential health concern in untreated source water. Contaminants that are regulated in drinking waters accounted for about 60% of the occurrences of both health benchmarks and unregulated contaminants accounted for about 40%.

Regulated contaminants are routinely managed by treatment or blending to lower concentrations before distribution. EPA uses USGS data in terms of unregulated contaminants as part of their process for determining whether specific contaminants should be regulated in drinking water in the future.

Kara: What contaminants did you find are a greatest concern?

Patricia Toccalino: Well, we found out that naturally occurring contaminants such as Radon and Arsenic accounted for about three-quarters of contaminant concentrations the levels of potential health concerns. This consist only one-quarter from man-made sources such as nitrate, pesticides and industrial compounds.


Kara: And which man-made contaminants were detected most often?

Patricia Toccalino: The most frequently detected man-made contaminants were disinfection byproducts, herbicides, solvents and compounds in gasoline but these compounds were usually found at low concentrations well below health benchmarks. We also found that contaminants usually coexist with other contaminants as mixtures. The presence of these contaminants in source water indicates that there are sources of contaminants in the environment and that there are pathways that allow the transport of contaminants from the land surface to ground water.

Kara: Well, so what does all this mean? Should people be worried about their drinking water?

Patricia Toccalino: The United States has one of the safest water supplies in the whole world. The Safe Drinking Water Act authorizes the EPA to set national health base standards for drinking water to protect against those naturally occurring and man-made contaminants.


The EPA, States, and water systems can work together to make sure that the standards are met. That said, the USGS did not assess the safety of drinking water, still our study suggests that some ground water resources may need treatments or blending before water is delivered to consumers.

Kara: How do you -- where can our listeners find out more about the quality of their water?

Patricia Toccalino: The best source of information about drinking water quality for people served by public water systems is their water suppliers. Water suppliers are required by the EPA to provide their customers with an annual water quality report.

Kara: And where can listeners find out more about this specific USGS study?

Patricia Toccalino: Well, the USGS National Water Quality Assessment Program website or their NAWQA Program website is a great place to start and that's or N-A-W-Q-A.


Kara: Patty, thank you so much for being here.

Patricia Toccalino: Thank you, Kara, my pleasure.

Kara: Don't forget to follow the USGS on Twitter at or visit our other social media channels at This CoreCast has been a product of the U.S. Geological Survey, Department of the Interior.

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