Groundwater Contamination

Once students understand that water moves around the planet through the water cycle, they discuss how human populations depend on fresh water for survival. However, there is a set amount of water on Earth, and fresh water is unevenly distributed around the planet. This water can become polluted, which creates problems for life on Earth.

• The amount of water is different around the world, from season to season, and from year to year. The amount of water in an aquifer changes over time.
• Groundwater is part of the hydrosphere and therefore interacts with other Earth systems.
• Human use of groundwater affects other living things as well.
• Aquifers are at risk of becoming polluted. Water pollution is the contamination of natural water bodies by substances that harm organisms and the environment, and it can be natural or caused by humans.
• Many of Earth’s aquifers are being depleted as human populations continue to grow.
• People who live in arid or semi-arid climates depend on the groundwater stored in aquifers.

• What causes an aquifer to recharge? What causes an aquifer to lose water?
• What makes an aquifer naturally balanced?
• Why can it be harmful to withdraw too much water from an aquifer too quickly?
• Why are people who live in arid or semi-arid climates more likely to access groundwater than people who live in wet climates?
• How do wells allow people to reach groundwater?
• How does pumping groundwater out of the ground affect natural ecosystems?
• How does human development—specifically the use of materials such as concrete and pavement, influences aquifers?
• How can groundwater become polluted?
• Why are confined aquifers less likely to become polluted than unconfined aquifers?

Misconception: Groundwater is stored in underground lakes.

Fact: Groundwater is stored in the pores that make up rocks, soil, and sand.

Aquifer discharge : when water leaves the aquifer, such as when it seeps into a spring

Aquifer recharge : when water seeps into the ground and replenishes the aquifer, such as from precipitation

Nonpoint-source pollution : pollution that is discharged over a wide land area and comes from many different sources and locations

Point-source pollution : pollution that can be traced back to a single identifying incident, such as a leak in an underground storage tank or waste discharging from a factory

Water pollution : the contamination of natural water bodies by substances that harm organisms and the environment

Water table : the highest point in an aquifer from which water can be obtained

Analyzing Data on Groundwater Resources

Groundwater pumping can harm ecosystems. The removal of groundwater impacts the quality of surface water. When people pump too much water from an aquifer, there is less water that is discharged to streams and rivers. This harms the aquatic habitats of many species, including fish and amphibians that live in streams.

Human development impacts groundwater resources in another way. Many human-made surfaces, such as pavement and concrete, are impermeable. When water falls to the ground, it cannot absorb into pavement or concrete. As a result, it does not reach the aquifers. This means it cannot recharge them.

Studying Groundwater

Scientists are trying to better understand groundwater on Earth. Groundwater is difficult to study because it is underground. It is also unevenly distributed around the planet. As a result, scientists map the geology and the underground structures of different areas. They want to understand how groundwater moves through different materials. They also want to see how quickly it is recharged in various locations.

To do this, scientists use deep wells up to 2,000 feet underground to monitor the groundwater and to observe what happens when additional groundwater is removed.

Polluted Aquifers

Scientists also study the effects of water pollution on aquifers. Water pollution is the contamination of natural water bodies by substances that harm organisms and the environment. It can be natural or caused by humans. Natural contamination can occur from naturally occurring mineral or metallic deposits in sediment.

Human pollution is caused by many different sources. Agriculture is one source of water pollution. Farmers add fertilizers and pesticides to increase crop production. When these chemicals are applied to a field, some of them enter the surface water. As a result, the water runoff will contain large amounts of pollution. This runoff can then seep into groundwater. There are two broad kinds of pollution: point-source pollution and nonpoint-source pollution. Point-source pollution can be traced back to a single identifying incident, such as a leak in an underground storage tank or waste discharging from a factory

Nonpoint-source pollution is discharged over a wide land area and comes from many different sources and locations. As water runoff moves over the ground, it picks up and carries away pollutants from many different sources. These pollutants can include excess fertilizers, pesticides, and oil spilled from vehicles or pipes.

Groundwater can become polluted in several ways. Surface water can become polluted from various sources, including oil, fertilizer, pesticides, and animal waste. As surface water seeps into the ground and becomes part of an aquifer, it can carry these pollutants with it.

The kinds of rock that surround an aquifer affects whether it will become polluted. There are two kinds of aquifers: confined aquifers and unconfined aquifers.

A confined aquifer has a layer of nonporous material between the water level and ground level that separates the water from ground level. This nonporous material is often clay or shale. This nonporous material acts as a buffer because water cannot move freely through it. Therefore, it can prevent or reduce the amount of pollution that reaches the aquifer.

In an unconfined aquifer, there are no layers of nonporous material between the water level and the ground level. These aquifers are more at risk of becoming polluted. This is because there is not an impermeable layer between them and the source of pollution. In other words, if anything leaks or spills into the soil above the unconfined aquifer, it will seep into and contaminate the water.

For the hands-on activity of this lesson, students build an aquifer model to simulate and observe the effects of surface water contamination on aquifer purity. Students use their observations to explain the role of gravity in the movement of water around the planet, how wells deplete aquifers, and how surface water can impact the purity of groundwater when the surface water is polluted.