9 Sources of Groundwater Pollution

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If you get your water from a private well, it’s important to be aware of the potential sources of groundwater contamination.

Here, we’ve shared the 9 common causes of contaminated groundwater, and how to prevent or treat groundwater pollution.

📌 Key Takeaways:

  • Some of the most common sources of groundwater contamination include hazardous waste, underground storage tanks, nearby septic tanks, rocks and soils, landfills, and water treatment plants.
  • Factors affecting groundwater pollution include your local geology, your proximity to industrial and agricultural sites, your well’s age and design, and how you use your land.
  • You can prevent or treat groundwater pollution by getting your well inspected and serviced, regularly testing for common contaminants, and installing a water treatment system.

❔ What Is Groundwater Pollution?

Groundwater pollution is when a groundwater source, such as a well or underground spring, becomes contaminated with pollutants (i.e. any substance with undesired effects).

Some types of groundwater pollution are more harmful than others. For instance, industrial or agricultural chemicals with toxic effects could have serious health ramifications if they’re ingested in groundwater, while certain natural metals found in the ground are less likely to be harmful to human health.

Different organizations have different definitions or pollution. Some refer to pollutants as only the harmful contaminants that enter water supplies. Here, we’ve defined pollutants as anything that may affect a groundwater supply, whether due to taste, health concerns, or aesthetic effects.

Illustration of groundwater contamination
Source: United States Geological Survey (usgs.gov)

💧 9 Sources of Groundwater Pollution

Natural effects and human activities can both cause groundwater pollution. Below, we’ve shared 9 potential sources of groundwater pollution to be aware of.

1) Rocks And Soils

Minerals from rocks and soils are a common cause of groundwater pollution.

When water seeps through the earth to the well aquifer, it collects traces of minerals from the rocks it travels through. These minerals depend on your local geology (i.e. the rocks that make up the earth beneath your property).

Examples of natural pollutants from rocks and soils include iron, fluoride, hydrogen sulfide, manganese, and chloride. Arsenic contamination may also occur due to natural levels of arsenic compounds in the earth.

2) Septic Systems

If you’re dependent on your own private well water supply for drinking water, there’s a good chance that you’re also dependent on a private septic system to manage your waste.

In the right conditions, a septic system shouldn’t pollute a well. However, if your septic tank is located too close to the well, the tank isn’t properly designed or is leaking, or the well is cracked or not properly sealed, there’s a potential for waste from the septic field to enter your groundwater supply.

There are several pollutants that can contaminate groundwater as a result of septic tank pollution, including bacteria, viruses, and nitrates. The contaminants could cause waterborne disease or have long-term health effects.

Septic drain field system installed close to well water

3) Hazardous Waste

Industries that produce hazardous waste are legally required to adhere to strict waste disposal practices.

Examples of hazardous waste include:

  • Swimming pool chemicals
  • Gasoline
  • Paint thinners
  • Industrial chemicals

If these materials are disposed of incorrectly (for instance, if they’re put into normal landfill), pollutants may be carried by rainfall to other areas and may seep through the earth into groundwater supplies.

The big industries can’t take the full blame for hazardous waste pollution – many careless or uninformed homeowners dispose of waste incorrectly on a small scale, and the small acts of a few people can quickly add up to have substantial, lingering effects on the local environment.

4) Storage Tanks Below Ground

You might have an underground storage tank on your property that holds heating oil, chemicals, or gasoline. This is especially likely if you’re living in a very remote location or you’re in the agricultural sector.

There are a few reasons why underground storage tanks might pollute your groundwater. Your well might be positioned too close to a tank, or the tank may corrode or develop cracks or holes that leak hazardous substances into the surrounding soil.

Even if you don’t have an underground storage tank on your own property, there may be several storage tanks in your local area, which may be responsible for your groundwater pollution.

5) Mining

If you live in a mining area, this could be another possible source of pollution for your local groundwater.

Mining sites have loosened topsoil, and when it rains, this soil is washed away, carrying sediments, metals, minerals, and sulfides into surface water supplies. Rainwater also leaches these pollutants into well aquifers as a result of soil seepage.

Toxic waste water from mining

6) Agricultural Activity

Agricultural activity is a common source of groundwater pollution in rural farming communities.

While many pesticides and herbicides have now been banned due to emerging research into their health effects, there are still hundreds of chemicals that are used, both in agricultural settings and on sports pitches and home gardens, which often end up polluting our groundwater supplies.

Over time, pesticides accumulate on the ground, and eventually seep into soil and collect in aquifers and groundwater springs. Nitrates and VOCs are also associated with pesticide use and could possibly pollute your groundwater.

7) Landfills And Waste Disposal Sites

A landfill or waste disposal site that isn’t properly designed or managed may release pollutants and hazardous chemicals, resulting in contaminated groundwater.

When waste materials decompose, they leach potentially dangerous substances, like heavy metals, chemicals, and other pollutants into the soil, where they eventually migrate into groundwater aquifers. Nitrate contamination affects wells all across the country.

8) Saltwater Intrusion

Groundwater resources in a coastal area may be affected by saltwater intrusion.

Saltwater intrusion occurs when groundwater is over-pumped, causing saltwater to infiltrate a freshwater aquifer.

Drinking water contaminated by saltwater intrusion may be unsuitable for ingestion by humans or use as irrigation water.

Illustration of saltwater intrusion in water well
Source: Investigation of Saltwater Intrusion in Coastal Aquifers, via Springer

9) Wastewater Treatment Plants

Facilities that treat wastewater release effluent that may contribute to groundwater contamination.

A plant may discharge wastewater near a groundwater well, or there may be subsurface connections between surface water bodies and groundwater supplies, causing contaminants in the discharged water to pollute underground water sources.

🔍 Factors Affecting Groundwater Pollution Sources

Here are some of the factors that affect your local groundwater pollution sources.

Your Local Geology

Your local geology plays a big part in the types of pollutants that end up in your groundwater.

For instance, if your local ground is predominantly limestone, you’ll likely have a lot of calcium in your water, which contributes to water hardness.

You might also have more fluoride naturally present in your local area, resulting in higher concentrations of this mineral in your water.

Your Proximity To Industrial & Agricultural Sites

Your proximity to industrial and agricultural sites will also affect your groundwater quality and the pollutants it may be exposed to.

For instance, if you live in an agricultural community, there’s a high likelihood that your water will contain pesticides, herbicides, and any other chemicals and pollutants that are used in your local farms, especially if proper waste management practices aren’t followed. These pollutants enter groundwater supplies as a result of surface runoff and soil seepage.

You’re also more at risk of groundwater pollution if you live in a region with heavy industrial activity. Factories may release pollutants into the air, where they eventually deposit into surface water sources, or they may discharge waste straight into rivers and lakes. These pollutants may eventually seep underground into groundwater supplies

Industrial water waste contaminated with chemicals

Your Well’s Age & Design

The age and design of your well may also affect its likelihood of getting polluted.

Older wells are likely to have compromised seals, cracks, or damaged components, allowing contaminants to pollute the water supply easily.

Some wells are simply poorly constructed, increasing your likelihood of groundwater pollution.

Or, your well location may make it more prone to contamination. For instance, if your well is located at the bottom of a hill, it’s more prone to runoff and flooding.

It’s important to get your well inspected regularly and repair any damage as soon as it’s detected.

How You Use Your Land

Your land use on your property is the final factor that affects your likelihood of groundwater contamination.

For instance, if you have an underground storage tank containing a hazardous substance, or a septic system that contains septic waste, there’s always a possibility that your well may become contaminated with the substances stored nearby. This is especially likely if you have an old or poorly maintained tank, or the well is positioned too close to the tank.

Also consider your use of lawn fertilizers and any other chemicals that could seep through the ground and into your well aquifer, causing groundwater pollution.

Keep in mind that anything you apply to your ground will not simply sit on the surface. It’ll eventually seep underground, so be mindful of what you use on your land.

Lawn fertilizers may seep into groundwater

🔬 How To Determine Your Groundwater’s Risk Of Pollution

Not all groundwater wells are at an equal risk of pollution, and, as you’ve now learned, not all wells are susceptible to the same pollution sources.

There are a couple of ways that you can determine your groundwater’s risk of pollution:

Speak To Your Local Authority

Your local authority should have shared plenty of information online about the possible pollutants in your area, and should alert you if and when your groundwater is at risk of serious contamination.

If you’ve just drilled a well or moved into a property with a well, contact your local authority with any questions you might have that you can’t find answers to online.

Check Aquifer Vulnerability Maps

Your state or local authority might have also produced aquifer vulnerability maps for your area to pinpoint any groundwater sources that might be particularly susceptible to contamination or pollution.

An example map is this groundwater vulnerability map of Ohio. If you can’t find a map for your state online, contact your local authority and ask if there are any public records that you can view.

🚫 How To Prevent & Treat Groundwater Contamination

Avoiding groundwater contamination will help you to protect your drinking water quality and minimize the cost of treatment. Here are our top recommended methods for treating and preventing groundwater contamination.

Get Your Well Inspected, Serviced & Repaired

One of the best ways to reduce the risks of polluted groundwater is to keep your well sealed against local sources of contamination.

The older your well, the more likely it is to become damaged, cracked, or corroded over time. Get your well inspected once a year to ensure it’s still structurally sound, and service or repair any components if an issue is detected.

Water well inspection

Test Your Water

Your annual well inspection should involve a test for common groundwater contaminants, including nitrates, coliform bacteria, dissolved solids, and pH levels, as per guidelines set by the Environmental Protection Agency. You should also test for any other pollutants that are known issues in your area, like toxic metals or chemicals.

Underground drinking water supplies can change in composition over time, so annually testing your water will help you to keep constant track of your groundwater quality and act fast if a dangerous pollutant is detected.

Water testing with tap score

Be Mindful Of Your Land Use

Since it’s often the case that groundwater contamination occurs as a result of improper land use above the groundwater aquifer, it makes sense that you can prevent the likelihood of contaminated groundwater by being mindful of your land use.

Any septic tanks should be at least 50 feet away from a well, and tanks storing hazardous waste or toxic substances should be stored at least 100 feet away.

If you use pesticides or any other lawn/plant treatment chemicals on your property, follow the usage instructions carefully and take measures to reduce runoff and seepage.

Drill A Deeper Well

Shallow aquifers are more susceptible to pollution because they’re closer to the surface of the ground.

So, if possible, consider drilling a deeper well to tap into an aquifer that’s located further beneath the ground.

Deep wells aren’t as likely to be polluted as shallow groundwater because water travels a greater distance to reach the aquifer, and is filtered through layers and layers of rocks and soils, which remove many of the culprits of surface water pollution.

Of course, drilling a deeper well costs money, and it’s not an option for everyone.

Install A Water Treatment System

You probably don’t have much control over many of the pollutants that enter your groundwater supply.

But while you can’t prevent contaminated groundwater, you can at least treat the water to make it safe to drink with an at-home water treatment system.

The type of system you buy depends on the cause of the water contamination. Here are a few possible water treatment systems to consider:

  • Whole-home iron filters, such as air or chemical injection/oxidation systems, which oxidize and remove iron, manganese, and hydrogen sulfide. Chemical injection systems also disinfect water.
  • Water softeners, which exchange calcium and magnesium minerals with sodium ions, preventing scale formation on your plumbing, appliances, and fixtures.
  • Reverse osmosis systems, which remove virtually all total dissolved solids, including nitrates and nitrites, chemicals, heavy metals, and bacteria.
  • Sediment filters, which remove particulates like sand, soil, rust, and other debris.
  • UV purifiers, which are a natural alternative to chemical disinfection, and kill most bacteria, viruses, and protozoa.

Many water treatment systems are expensive, but they’re an essential investment if you want to protect your family from many of the common groundwater pollutants.

At-home water treatment systems

🔚 Final Word

Groundwater pollution isn’t as likely as surface water pollution, but if you own a private well, it’s still important to educate yourself on the possible sources of pollution and take action to prevent contamination and treat your water if necessary.

  • Brian Campbell
    President & CEO, CWS, CWR

    Brian Campbell, a WQA Certified Water Specialist (CWS) and Certified Water Treatment Representative (CWR) with 5+ years of experience, helps homeowners navigate the world of water treatment. After honing his skills at Hach Company, he founded his business to empower homeowners with the knowledge and tools to achieve safe, healthy water. Brian's tested countless devices, from simple pitchers to complex systems, helping his readers find the perfect fit for their unique needs.

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