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Groundwater quality

GCC Report to the Legislature

Groundwater pollution from human activities and natural sources happens across Wisconsin. This is of particular concern for the 70% of Wisconsinites who get their drinking water from groundwater.

Other groups concerned about groundwater quality include farmers who rely on safe groundwater for crop and livestock production, and business owners who rely on groundwater for manufacturing and commerce. Lakes, rivers and streams are fed by groundwater. Fish and wildlife can't thrive when groundwater contaminants impact the surface water they are dependent upon.

We continue to learn more about groundwater quality in Wisconsin through research by collecting information about the occurrence of different substances found in groundwater and their impacts on human and environmental health.

Common Contaminants - Usually Acute Health Effects

Bacteria, viruses and other pathogens

Escherichia coli.
Escherichia coli. Photo credit: National
Institute of Allergy and Infectious Disease.

Pathogens are organisms or other agents that can cause disease. These include microorganisms such as bacteria, viruses and protozoa that can cause waterborne disease. Groundwater contamination by microbial pathogens can often be traced to human or livestock fecal waste that seeps into the ground from sources such as poorly constructed or failing septic systems, leaking sanitary sewers or improperly managed animal manure.

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Tractor in a field
Photo credit: DNR.

Nitrate is Wisconsin's most widespread groundwater contaminant. Nitrate contamination of groundwater is increasing in the state. About 90% of nitrate in groundwater is due to agricultural inputs, including manure spreading and fertilizer application.

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Common Contaminants - Usually Chronic Health Effects


Pyrite. Photo credit: JJ Harrison.

Arsenic occurs naturally in soil and rock, typically bound to other minerals such as pyrite (pictured). Under certain environmental conditions, arsenic can dissolve and be transported in groundwater. It can also be released as a by-product of agricultural and industrial activities.

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Pesticide application by plane
Photo credit: DATCP.

Pesticides are a broad class of substances designed to kill, repel or otherwise disrupt living things that are considered pests. Normal field applications, spills, misuse or improper storage and disposal can all lead to pesticide contamination in groundwater. In Wisconsin, the main source of pesticides in groundwater is agricultural herbicide and insecticide applications.

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Naturally Occurring Elements - including Radionuclides, Chromium, Manganese & Strontium

Radio Active Symbol
Photo credit: Pixabay.

Radionuclides are radioactive atoms. It is possible for radionuclides to be manmade but they also occur naturally in rock formations and are released to groundwater over millions of years by geochemical reactions. Since they occur naturally in rock formations, every well in Wisconsin contains some level of dissolved radionuclides. In many places, these levels are not concerning, but some areas of the state tend to have notably high concentrations. Other examples of natural contamination in Wisconsin are radium in southeastern Wisconsin, chromium in Dane County, manganese and strontium.

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Volatile Organic Compounds (VOCs)

Volatile Organic Compounds (VOCs) tank
Photo credit: DNR.

Volatile Organic Compounds (VOCs) are a group of common industrial and household chemicals that evaporate or volatilize when exposed to air. Examples of products containing VOCs include gasoline and industrial solvents, paints, paint thinners, air fresheners and household products such as spot and stain removers. Improper handling or disposal of VOCs is often the reason why they appear in groundwater. At least 59 different VOCs have been found in groundwater in Wisconsin.

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Additional Contaminants

Emerging Contaminants

Pill bottles
Photo credit: US Department of Defense.

Emerging contaminants are compounds that are increasingly being detected in groundwater and may have harmful human health or environmental impacts. Examples include pharmaceuticals and personal care products, PFAS, pesticides and microplastics. Many, but not all, of these emerging contaminants enter the groundwater from wastewater or solid waste sources.

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Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)

Firefighters spraying foam on structures.
Firefighters spraying foam.

PFAS are a large group of human-made chemicals that have been used in industry and consumer products worldwide since the 1940s. Their ability to repel water and oil and withstand high temperatures has made PFAS a useful ingredient in products including non-stick pans and water-repellent clothing. These chemicals do not easily break down in the environment and have been known to accumulate in the environment and humans. Humans may be exposed to PFAS in several ways, including drinking municipal or private well water contaminated by PFAS.

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Additional Resources