Official State of Iowa Website

Contamination in Karst

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Why you should read this web page

Good quality drinking water is one of the building blocks for good health. Understanding your drinking water quality can help protect the health of you and your family. You should read this web page if you consume water from a private water well that is finished in any shallow aquifer.  Shallow aquifers are more susceptible to contamination due to their close proximity to the ground surface and the influences caused by local land use activities.

Why this topic is important

Even though your water may look clear and taste good, you will not know if it's safe to consume unless you take the necessary steps to confirm it's safe.

For those connected to a public water supply, the water supply operator performs routine testing and informs the water users if the water is not safe to consume. For private wells, the responsibility of water testing falls solely onto the well owner and anyone else who uses the well water. This means you - as a well user - need to take the steps to ensure that your water supply is tested for the contaminants that may be present in your local area and inform yourself by understanding the analytical results provided by the testing laboratory.

Anyone who consumes unsafe water may experience health issues. Your risks increase if your water is over the EPA maximum contaminant level (MCL) for any contaminant and when you consume contaminated water for longer periods of time.

The potential problem

Some wells finished in shallow aquifers can contain high levels of bacteria, nitrates, pesticides and other chemicals and organisms. Any of these contaminants can adversely impact health if consumed.

Even older wells finished in currently safe aquifers can be affected when steel well casing used in the well's construction corrodes and the casing develops small leaks that allows poor quality shallow groundwater to enter the well.

Many farms and homes in Iowa obtain their water from bedrock wells. Deep bedrock wells are generally safe water supplies because they tap deeper aquifers that have natural geologic barriers in place that helps keep contaminants from entering the aquifer. But in some areas of our state, shallow bedrock aquifers exist. Some of this bedrock is defined as "Karst".

Karst bedrock is characterized as bedrock that is close to the land's surface and contains a vast network of underground drainage systems that have direct connections to the land's surface.

In areas of Karst, much of the rainfall that would normally flow to rivers and streams, directly or indirectly flows into the shallow bedrock and becomes part of the groundwater some water wells may utilize. Some of the water that originates at the surface - possibly near sources of contamination - flows undetected into the ground.

This water can contain contaminants that are found on the land's surface and those not bound or utilized by the areas soils and land cover. Once in the ground, this water that was once on the surface becomes part of the groundwater supply.

A well that obtains part or all of its water from a shallow aquifer can have higher levels of contaminants when compared to deeper wells in the same area.

Anytime you consume water that contains unsafe levels of any contaminant, you increase your risk for negative health effects.

NE Iowa Karst Map

NE Iowa Karst MapThis map shows the areas of northeast Iowa where Karst bedrock is likely to occur.

Shallow wells located in areas of Karst bedrock can have poor water quality.

The darker shaded areas are those where sinkholes and bedrock exposures are most likely and water quality concerns are the greatest in shallow bedrock aquifers.

Click on the map to view a larger image.

The areas affected

Shallow aquifers are less protected than deeper aquifers. Karst bedrock aquifers are some of the most susceptible to contamination. Although Karst features can be found in a number of locations across Iowa, they are most abundant in the NE corner our state.

Whether or not your well may be affected will depend on a number variables, like:

  • The location of the well.
  • The well's finished depth.
  • The actual aquifer(s) the well taps.
  • The well's primary casing depth.
  • The presence of casing grout around the well casing.
  • The age of the well.
  • And the historic and current land use activities nearby the well.

In general, if you use a shallow aquifer for your water supply, you may be affected. If your well is located in one of the shaded areas of the NE Iowa Karst Map on this page and obtains any of its water from the shallow aquifer, your well has the potential to be influenced by Karst groundwater. Regardless of location, shallow well users should test their well water to make sure it's safe to consume.

Karst from the air

Iowa Geological Survey aerial image showing sinkholes

This aerial image is of a Karst landscape in Clayton County. The small depressions or dimples you see are sinkholes.

This type of feature can allow surface water rapid access to shallow groundwater where it affects groundwater quality. Image courtesy of the Iowa Geological Survey.

The Challenges with Karst

Because of the potential for surface water influence and the types of land use activities that may take place in Karst regions, localized shallow groundwater may contain infectious bacteria, viruses, agricultural or industrial chemicals, and other hazardous agents. 

In addition, the groundwater flow path through Karst bedrock can be unpredictable. This means that some shallow wells in Karst areas may be unaffected by contaminants while other wells show signs of contamination.

Those who use shallow bedrock wells located in the darker shaded areas of the NE Iowa Karst Map on this web page should note that this is where Karst activities are most likely to occur. There is a significant increase in the number of sinkholes and other Karst features in these areas.

Constructing and maintaining a well in Karst areas requires greater care to ensure your drinking water comes from a deep, safe aquifer using construction standards that help protect your drinking water quality and the aquifer.

How surface water becomes groundwater in Karst areas

Normally, rain events create surface water that runs-off into rivers and streams and is absorbed by soils and till. But in areas of Karst, the run-off can rapidly flow into the bedrock - either directly through shallow openings and surface sinkholes, as well as vertical and horizontal fractures or solution channels that are exposed near or at the ground's surface, or indirectly through the pore openings and areas of thin soil overlying the limestone bedrock.

In most areas, we depend on the soils to act as a filter in which biological and chemical interactions take place that help improve the water's quality.

But in areas of Karst, there is little or no soil for the water to flow through before reaching the shallow aquifer. This means there is little or no filtering or treatment that takes place before the water mixes with the shallow groundwater.

In addition, when water flows directly into the bedrock via sinkholes, losing streams and a system of voids or fractures that reach deep into the ground, there is no filtering that takes place before the water mixes with the shallow groundwater.

Once in the ground, the water rapidly flows through the large openings in shallow bedrock which further reduces any opportunity for the water to undergo natural water treatment.

When surface water moves into a shallow aquifer, the potential for poor well water quality in the aquifer increases.

Karst below the surface

Image of groundwater in Karst bedrock

This diagram provided by Iowa Geological Survey shows a cross section of a Karst bedrock setting. You can click on the diagram to view a larger image.

The dark blue areas indicate groundwater stored in openings of the bedrock. This groundwater is part of the shallow aquifer and available to the well visible in the diagram.

You can see the open spaces in the bedrock blocks that allows for storage and transport of the groundwater. You can also view how the land surface and stream visible in the diagram can directly interact with the water stored within the bedrock.

In Karst systems, soil infiltration, surface water run-off and streams can drain directly into the shallow bedrock and become part of the shallow groundwater and aquifer.

This means that the contaminants found on the land surface and in surface water, may also be present in wells that draw water from the shallow aquifer.

How to find out if your water is safe

The only way to determine if your well water is safe to consume is to take a sample of the water and send it to a drinking water laboratory.

Your local county environmental health office can help you arrange for testing or you can obtain a water sample test kit, sample the water yourself and send it to a certified drinking water laboratory for analysis.

The primary indicator tests normally performed include coliform bacteria, nitrate, and nitrite. Testing for these contaminants is easy, inexpensive and can be used to provide basic information on drinking water safety.

There are also other water tests you should consider. Contaminants like arsenic, fluoride, radium, and lead are naturally occurring in some aquifers and may require specialized water treatment to reduce or eliminate the exposure risk.

You should also consider testing shallow wells periodically for pesticides.

  • Pesticides are mostly modern chemicals that are used to control weeds and insects, and improve crop and turf production. Pesticides are used on farms and in communities. You likely have a number of pesticides that you use routinely in and around your home.
  • Atrazine is one of the most commonly found pesticides discovered during well water analysis. You can learn more about Atrazine in drinking water and health concerns that may be attributed to this chemical by visiting the CDC Atrazine Information web page.
  • Volatile Organic Compounds (VOCs) such as gasoline, vinyl or plastics, adhesives, dry-cleaning fluids, refrigerants, paints and solvents.
  • Animal waste like manure and compost.
  • Or a number of emerging contaminants that may be linked to our modern lifestyle and activities.

Private wells do not fall under mandated state or national water quality standards. Because of this, you should use the Environmental Protection Agency (EPA) contaminant standards for public water supplies as the recommended standards for your private water supply.

The presence of any contaminant above the EPA's maximum contaminant level (MCL) means that you should not consume the water without proper treatment, water system repairs that eliminates the source of contamination, or replacing the well with one constructed to provide safe water.

For more information on specific water testing you may want to consider, please contact the State Hygienic Laboratory at the University of Iowa, 800-421-4692, or any other Iowa certified drinking water laboratory, your local Iowa DNR Certified Well Contractor or the Iowa DNR.

Lab analysis

Lab Professional Testing WaterThis image from the State Hygienic Laboratory shows a lab technician performing water analysis.

Laboratory analysis of drinking water requires controlled conditions, expensive technical equipment and highly trained professional staff.

What's in a Water Test Kit?

Image of what comes in an SHL well water test kit

This photo shows what's included in a water sample test kit when obtained from the State Hygienic Laboratory. It consists of sampling bottle(s), a request form and mailing materials.

All drinking water samples must be analyzed by a State Certified Drinking Water Laboratory.

There are currently over 40 certified labs who can provide water analysis for private well owners.

There is a statewide grant program called the Grants to Counties Water Well Program that can provide you with basic water testing for free. For more information, please contact your local county environmental health specialist.

The risk you take when you consume unsafe water

You increase your risk for illness and disease if you drink contaminated water. Each type of contaminant has its own health impacts depending on the level of contamination, how much of the contaminated water you consume and your individual sensitivity to the contaminant(s).

Here is some basic information on the most commonly detected contaminants.

  • Bacteria, viruses and protozoa are microorganism groups that contain pathogens that can cause waterborne diseases. When these microbes are present in your water supply, symptoms such as diarrhea, cramps, nausea, headaches and others are possible. Microbes can pose a much greater health risk for infants, young children, senior citizens and those with severely compromised immune systems.
  • Nitrate in drinking water above 10 mg/L when tested for nitrate nitrogen (NO3-N), should never be given to infants less than six months old as it can cause a potentially fatal disease called “blue baby syndrome". There are also indications that long term exposure to nitrate levels exceeding the MCL may lead to other health issues, but more research is needed in this area.
  • Arsenic. Studies have shown that chronic or repeated ingestion of water with arsenic over a person’s lifetime is associated with increased risk of cancer of the skin, bladder, lung, kidney, nasal passages, liver or prostate, and noncancerous health effects like diabetes and cardiovascular, immunological and neurological disorders.
  • Other contaminants. EPA has a website available that contains a list of common contaminants and the potential health risks associated with each. You can view the website at the following web links: http://www.epa.gov/ccl/types-drinking-water-contaminants and http://www.epa.gov/dwstandardsregulations/drinking-water-contaminant-human-health-effects-information.

For additional information on water borne diseases please see the Centers for Disease Control, Iowa Department of Public Health or your local county environmental health office.

Contaminants

Water-related diseases and Contaminants that may be found in unsafe drinking water.

Source - The Centers for Disease Control and Prevention

Managing Risks

Knowledge of your water quality will empower you and help you make informed decisions about your consumable water and long term health.

First and foremost, ensure that all the water you consume is safe. Laboratory analysis of your well water is the only way to determine this. Your local county environmental health specialist or certified drinking water laboratory can help you decide which tests make sense for your well depth and location.

How often you test your supply should be based on several things. They include what your previous water testing found, who is using the water, changes in the water quality you can see, taste or smell, and the type of potential contaminants applied to land near your well.

At a minimum, all private well users should test their water supply at least once each year for a minimum of coliform bacteria and nitrates, and have at least one arsenic test performed on the well water.

You should test your well more often if:

  • You suspect or know your well obtains part of all of its water from a shallow aquifer or Karst bedrock.
  • Previous testing found contamination and the level of contamination was near maximum recommended MCLs or above the MCLs.
  • You have young children, senior citizens or immune compromised individuals using the water.
  • Your water quality suddenly changes. Things like unusual tastes, odors, color or sediment.
  • You have any well repair or pump and water system services performed.
  • Neighboring wells of similar depth and construction have tested positive for contamination.
  • One or more of your family members become ill and the symptoms do not seem to improve within a time period that seems normal based on your previous experiences.

If your water analysis finds the water is unsafe for any contaminant, do not drink the water. You should obtain all of your drinking and consumable water from a known safe water source, like a well recently proven safe by water testing and analysis, a water treatment device connected to your water supply that is designed to remove the contaminant(s) found, a public water supply, or buy bottled water. This reduces or eliminates your immediate risk and allows time for you to investigate the long term options for managing your water system.

Water Treatment Options

State Hygienic Lab Water Treatment Guide

This informational booklet by the State Hygienic Laboratory at the University of Iowa provides a guide to well water contaminants and effective water treatment devices.

Well Consumer Information Booklet

Iowa Private Well Consumer Information Booklet

This booklet is designed to help private well owners understand private well construction and ownership.

Consumable Water

The term "consumable water" includes:

  • Water you drink.
  • Water used for mixing beverages.
  • Water used in food preparation activities.
  • Water in ice cubes.
  • Water used to brush teeth and rinse mouth.
  • Water used for child's play.
  • And depending on the type and level of contamination, water used to wash dishes, wash hands, and shower or bathe.

Short-term options

Short term options if your water supply is contaminated-
  • Use the well only for purposes it does not pose any health risk and use bottled water for all consumable purposes.
  • Install and maintain approved water treatment devices at each tap you obtain consumable water.
  • AND regardless of which method used, contact an Iowa DNR Certified Well Contractor for consultation about your water supply.

Long Term Options

Long term options if your water supply is contaminated-
  • First, contact an Iowa DNR Certified Well Contractor for consultation. They can help you make informed decisions like:
  • Can you modify your existing well to keep-out the poor quality water?
  • Do you need to replace your well with a new well that includes additional construction features designed to improve your water quality?
  • Is it possible to install and maintain approved water treatment devices at all taps where you obtain consumable water?
  • Is it best for you to connect to a nearby public water supply if one is available?
  • And as a last resort, can you use the well only for purposes where it does not pose any health risk and use bottled water for all consumable purposes?

Fact Sheet

Fact Sheet

Fact Sheet

Fact Sheet

Iowa's Groundwater Basics

Iowa's Groundwater Basics published by the Iowa Geological Survey is a geological guide to the occurrence, use and vulnerability of Iowa's Groundwater.  The publication is full of good information, interesting diagrams and wonderful pictures.

Image of Iowa Groundwater Basics

Contamination in Karst

 

Additional Resources

 

 

- For more information contact -

Erik Day
Water Supply Engineering Section 
Wallace State Office Building 
502 E. 9th Street, Des Moines, IA 50319-0034 
515-402-7981