The USGS Water Science School
Contamination in U.S. Private Wells
Groundwater is one of the Nation's most important natural resources and is an important source of drinking water for mostly-rural populations that supply their own domestic water from local wells. In 2005, about 43 million Americans supplied their own home water and over 99 percent of that water came from groundwater. Naturally, the quality and safety of water in these wells is an issue of concern, and in 2009, the U.S. Geological Survey (USGS) studied the water quality of over 2,000 private wells to measure the existence and extent of contamination. The study found that about 23 percent of them did have at least one contaminant at a level of potential health concern.
Contaminants in 20 Percent of U.S. Private Wells
A podcast of this interview is available in the U.S. Geological Survey's multimedia gallery.
In March of 2009, USGS media specialist Jennifer LaVista sat down with USGS scientist Leslie Desimone to discuss the study. The transcript of their discussion appears below.
USGS scientist Leslie Desimone discusses the new study, the contaminants found, and the implications for society.
Jennifer LaVista: About 43 million people, or 15 percent of the nation's population, use drinking water from private wells, which are not regulated by the Federal Safe Drinking Water Act. But the quality and safety of the water in these wells may be an issue of concern, according to a new US Geological Survey study. Can you tell me about some of the major findings of the study?
Leslie Desimone: Our findings are based on about 2,100 private wells that we sample from across the country. We measured many different contaminants in those wells. Everything from chloride to organic compounds, like the chemicals that make up gasoline. And we found that, while most of the wells did not have any of these contaminants at levels of potential health concern, about 23 percent of them did have one or more contaminants at a level of potential health concern.
Leslie Desimone: And the contaminants that were most frequently at those levels were mostly from natural geologic sources, coming from the rocks and sediment that make up the aquifers from which the wells were drawing water—things like radon, arsenic, uranium, manganese and nitrate. Nitrate is a little different in that it does have natural sources. Usually when it's present at this high levels of health concern, it comes from man-made sources like septic tanks or fertilizer.
Jennifer LaVista: OK. So, agricultural causes.
Leslie Desimone: Certainly we did find nitrate concentrations higher in areas of agricultural land use than elsewhere.
Jennifer LaVista: Can you elaborate a little bit more about some of the contaminants that have potential health concerns?
Leslie Desimone: One of the ones that we found in a concentration that might be a health concern in some of the wells is radon. Radon is a radioactive gas and it poses a problem in drinking water. Not when you drink it really, but when it comes out of solution, when water is used. For example, when you take a shower. Some of the other contaminants are a problem when you drink them, like arsenic. Arsenic we always think of as a poison, but it's also a carcinogen. And it's a problem when you drink the water with high concentrations of arsenic.
Jennifer LaVista: Now, is radon a carcinogen as well?
Leslie Desimone: Yes. Radon is a carcinogen.
Jennifer LaVista: So, the public should be concerned about this problem.
Leslie Desimone: Well, certainly if you have a private well and that's where you get your drinking water, you should be concerned about the quality of the water from the well. And you should have it tested to make sure they aren't any contaminants at levels of health concerns. You should be aware of the possibility that contaminants can occur even if your well is an area that doesn't seem particularly vulnerable to groundwater contamination. For example, because it's in an area that always been undeveloped, other than a house here and there.
Jennifer LaVista: So, what can well owners do?
Leslie Desimone: Well, they can have their water tested on a regular basis. But there's also many sources of information for private well owners. And although private wells aren't regulated by state agencies, many state environmental protection agencies and public health agencies have information and websites available for private well owners. And these websites provide information about well construction techniques and recommended testing procedures.
Jennifer LaVista: Did the study find any trends or patterns?
Leslie Desimone: Well, we did find that some contaminants are more of a concern in some geographic areas than others. And as I mentioned, nitrate in areas of agriculture is a concern. Some of the naturally occurring contaminants are more prevalent in some aquifers than others. For example, radon is more prevalent in some aquifer types that we call crystalline rock aquifers.
And we found those in the northeast, in the central and southern Appalachians, and in an area of Colorado. So, if your well is drawing water from one of those aquifers, you might find that radon is more of a concern. Whereas, if your well is drawing water from a different kind of aquifer, for example a sandstone aquifer, radon may not be much of a problem. One of the other findings that the study showed was that the contaminants don't usually occur by themselves in well water. They occur with other contaminants as mixtures, although typically at low levels—at levels that, individually, wouldn't be a health concern. But, there's not a lot of information about the health effects of low level mixtures. And this is an area really where further research is needed.
Jennifer LaVista: Are there any follow ups to this plans?
Leslie Desimone: Within the USGS NAWQA program, there are a number of studies that are looking in detail at the distribution of some of these contaminants in groundwater generally in principal aquifers across the country. And those studies are trying to understand the sources and processes that affect the mobility of some of those contaminants. Although, they're not focusing specifically on private well.
Jennifer LaVista: Where can our listeners learn more about the study?
Leslie Desimone: For more information about the USGS study that we're talking about right now, we have a website that has links to the two published USGS reports, as well as maps and graphics and some other information that might be helpful. For people who are interested in finding out more about private wells and contaminants that can occur in them, the APA and CDC have websites with information for private well owners. Many state agencies and non-governmental organizations have information as well.
Jennifer LaVista: That's really helpful. Is there anything you'd like to add?
Leslie Desimone: Well, I think that the findings of this study really pour into the importance and the responsibility of homeowners to test their well's water quality and pay attention to it because really it's up to them to ensure that the quality of the well water is good.
CoreCast is a product of the USGS Geological Survey Department of the Interior.
I'm Jennifer LaVista.