Private Well Protection Arsenic Study
Clean Water Fund

Approximately 10 percent of new wells in Minnesota contain arsenic above the drinking water standard. Drinking water with low levels of arsenic over a long time increases the risk of diabetes and increased risk of cancers of the bladder, lungs, liver, and other organs. It can also contribute to cardiovascular and respiratory disease, reduced intelligence in children, and skin problems, such as lesions, discoloration, and the development of corns. Health impacts of arsenic may not occur right away and can develop after many years, especially if you are in contact with arsenic at a low level over a long time.

Arsenic can be found in groundwater throughout Minnesota, but is more likely in some areas than others due to the way glaciers moved across Minnesota. Because it has no taste and no odor, testing is the only way to know whether or not a well has arsenic in it. All new wells must be tested for arsenic before being placed in service.

The Minnesota Department of Health (MDH) Well Management Program used funding from the Clean Water Fund to conduct an arsenic study to better understand arsenic in Minnesota well water in order to reduce risk to private well owners.

Arsenic study goals

• Determine how water sampling methods and the timing of sample collection contribute to arsenic test results in a new well.
• Collect water samples to track variation in arsenic concentration in a new well up to a year after the initial sampling date to see how long it takes the water chemistry to stabilize.
• Identify the conditions that control arsenic occurrence in groundwater.
• Provide guidance and education to well contractors and private well owners to reduce risks from arsenic in well water.

Results

There are 264 private wells included in this study. The results are as follow:

• Of the 264 well results, seventy-five wells exceeded the arsenic limit allowed in public water supplies—maximum contaminant level (MCL). Twenty-eight percent exceeded the MCL of 10 micrograms per liter).
• Of the 251 follow-up sample results, seventy-five wells exceeded the MCL (30 percent).
• Of the 245 final well results, sixty-nine wells exceeded the MCL (28 percent).
• When the initial arsenic result was above the MCL, four percent of the final arsenic results a year later dropped below the MCL.

Next steps

• MDH will use the results from the arsenic study to develop outreach and communication materials for private well users about arsenic in their well water and the best sampling timing and method.
• MDH will collaborate with the U.S. Geological Survey to publish the results in journal articles and to share the findings with the public and research communities.

Additional resources

• Arsenic in Drinking Water
• Arsenic in Private Wells: Facts and Figures

Of interest

• Check out the Key Water Information Catalogue

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