What is Groundwater Contamination and How Do You Treat It?

Posted by
John Woodard on February 16, 2021
Groundwater is a hidden resource. It exists underground in fractures and spaces between rocks and soil known as aquifers, but even though it is out of sight, the importance of groundwater should not be underestimated. Groundwater is the largest source of freshwater on the planet and provides drinking water to over 50% of the world’s population. Once contaminated, groundwater is costly to restore, so it is important to protect this valuable natural resource. Below you will learn about groundwater contamination and its lasting effects, how to treat contaminated groundwater, and how to prevent future pollution.

What is groundwater?

Groundwater is water that dwells underground in the cracks and spaces between rocks and sediment. Most groundwater comes from precipitation. When it rains or snows and soil becomes saturated, water percolates downwards to aquifers and replenishes the groundwater supply. Groundwater then moves slowly through the earth until it naturally resurfaces in lakes, rivers, and streams, or is drawn to the surface through man-made wells. Groundwater is a vitally important resource. Not only does it provide drinking water for over half the world’s population, but also the majority of farmlands rely on groundwater for irrigation. However, groundwater is vulnerable to both overuse and contamination.

Groundwater Diagram

What is groundwater contamination?

Groundwater contamination occurs when pollutants, such as gasoline or pesticides, reach groundwater and render it unsafe or unfit for human use. Any activity that releases chemicals and pollutants into the environment has the potential to contaminate groundwater, and human activity is almost always the culprit. Groundwater is most vulnerable to contamination in areas that have a high population density and intensive land use.

What contaminants are found in groundwater?

The following list details common contaminants that can be found in groundwater.

  • Microorganisms, such as bacteria, viruses, and parasites
  • Heavy metals, such as arsenic, copper, lead, iron, and manganese
  • Pesticides, herbicides, and insecticides
  • Oil and gasoline
  • Household products, such as paint thinner and swimming pool chemicals
  • Nitrate and nitrite
  • Volatile organic compounds (VOCs)
  • Chloride
  • Fluoride
  • Cyanide
  • Sulfate
  • Radionuclides

Sources of groundwater contamination

Groundwater contamination is caused by both natural sources and human activity, but the latter is usually the culprit. Below are six common sources of groundwater contamination.

1.      Natural sources

When water flows underground, it absorbs substances, such as iron, manganese, chlorides, and fluorides from rocks and soil.

2.      Septic systems

Septic systems are one of the main causes of groundwater contamination in the United States. Septic systems that are improperly designed or maintained can contaminate groundwater with bacteria, viruses, nitrates, and many other unpleasant contaminants.

Learn More: How to Remove Bacteria from Drinking Water

3.      Improper disposal of hazardous waste

If hazardous wastes, including paint thinner, swimming pool chemicals, and gasoline are disposed of in a standard landfill, chemicals can leach into the soil and eventually into the groundwater. To prevent dangerous contamination, contact your local waste management company to find out where to safely dispose of hazardous waste.

4.      Underground storage tanks

Underground storage tanks are often used to store gasoline, heating oil and other chemicals. For example, municipal highway departments use them to store gasoline and diesel. Currently there are about four million underground storage tanks throughout the United States. As tanks age, they may corrode and leak hazardous substances into the soil and groundwater.

5.      Mining

Mining produces waste that often contains metals, minerals, and sulfides. When it rains, the wastes leach into the groundwater below.

6.      Pesticide and fertilizer use

Pesticide and fertilizer use is widespread. They are not only used in agriculture and by farmers, but also by homeowners, cities, businesses, and even golf courses. As these chemicals accumulate on lawns and crops, they seep into soil and eventually migrate to groundwater. Their pollution is augmented, as some pesticides even release VOCs. If you live in an agricultural area and have a well, your water supply is especially prone to contamination from agricultural runoff, such as nitrates and VOCs.

Learn More: What are VOCs and How Do You Remove Them?


Groundwater Contamination

What are the effects of groundwater contamination?

Groundwater contamination can result in poor water quality, expensive cleanup costs, and at worst, loss of water supply and potential health problems. Depending on the severity of the contamination, a groundwater supply may have to be abandoned as a source of drinking water. If groundwater can be restored, it costs thousands to millions of dollars and the water quality will have to be monitored for years to come.

Health effects vary depending on the types of contaminants present, but all should be taken seriously. Drinking water contaminated with bacteria and viruses can cause gastrointestinal distress and diseases, such as hepatitis. A high level of nitrates and nitrites can cause methemoglobinemia (also known as “blue baby syndrome”), which means an infant’s blood is poorly oxygenated. Exposure to certain contaminants, such as gasoline, heavy metals, and radionuclides, can even increase the risk of cancer.

Learn More: How to Remove Nitrates from Water

Who is at risk for groundwater contamination?

Well owners are at a greater risk of groundwater contamination than those who use a municipal water supply. Wells are often located in agricultural and rural areas where the chances of agricultural runoff, mining, and septic tank use are higher. Not only are certain groundwater contaminants more prevalent in rural areas, but also well owners are responsible for safeguarding their own water supply and must practice vigilant water testing. Whereas, if a municipal water source is contaminated, the burden is on the municipality to address the issue.



How does well water get contaminated?

Contaminated groundwater from underground aquifers and pollutants from the surface can contaminate well water. Most wells get their water from aquifers, so if an aquifer contains contaminated groundwater, the contaminants will be introduced to any connected wells. Also, if there is heavy rain, surface run-off can wash above ground pollutants into a well system. Private wells are not regulated, so it is the responsibility of the well owner to test for contaminants and to ensure a safe drinking water supply. Given the potential for contamination from above and below, a home water test kit or a lab water analysis are recommended to keep tabs on a well’s water quality. If you live near a mine, an industrial site, or farmland, the risk factor for well contamination is higher, so it is important to be aware of your surroundings and to test your water regularly.

Learn More: How to Remove Iron from Well Water

How to test for contaminants in groundwater

Most groundwater is brought to the surface by pumping it through a well, so testing well water is the easiest way to reveal contaminants in groundwater. If contaminants are present in a well’s groundwater source, they will be drawn into the well and also inflict its water quality.

How is contaminated groundwater treated?

Contaminated groundwater is treated through groundwater remediation. There are two types of groundwater remediation: in situ (on site) or ex situ (off site). In situ remediation is often called bioremediation, as it involves introducing microorganisms to the groundwater that destroy or detoxify inorganic and organic contaminants. The water is treated precisely where it is located. Ex situ remediation is often called “pump and treat.” In this method, groundwater is physically pumped out using a vacuum pump, then purified off site, and lastly returned to the aquifer below. Both methods should be performed by a professional water remediation company.

However, groundwater remediation is difficult and very expensive, usually costing thousands to millions of dollars. Not to mention, a once contaminated groundwater source must be monitored for years to come. Preventing groundwater contamination in the first place is the ideal treatment method.

How to prevent groundwater pollution

Prevention is key in combatting groundwater pollution. There are a few simple steps that everyone can take to prevent contaminants from entering the groundwater supply and to maintain a healthier environment.

  • Properly dispose of all waste: don’t dump chemicals down the drain. Instead, contact your local health department to find a hazardous waste collection site near you.
  • Safely store all chemicals, fuel, paint, and pharmaceuticals.
  • Minimize chemical use and always use chemicals according to directions.
  • Frequently inspect underground storage tanks and septic systems for leaks.
  • Plant grasses and plants that are native to your region. They are naturally adapted to your area's climate and therefore do not require a lot of fertilizer, pesticides, or herbicides.


If you would like to learn more about groundwater contamination and how you can best protect your water supply, we are here to help. Please contact us with any questions you may have.

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