Who's Down the Well

It is a complex process to create a good glass of drinking water. Drinking water directly from a well or surface source (such as a lake, river or stream) may contain harmful contaminants that can cause illness or even death or the organisms that consume the water. Can you think of some examples of contaminants? Some contaminants can occur naturally, such as metals from rock erosion or microorganisms; some contaminants come from human activity, such as fertilizer or roadway run-off or chemical discharge from industrial plants and factories. When these contaminants are present in drinking water, they can become dangerous to plants and animals.

Civil, environmental and chemical engineers work together to design drinking water treatment facilities to prepare safe drinking water that is distributed to our homes. To do this, they find existing sources of water, design safe pathways to reach those sources, and decide how to clean any contamination. Today, we will look at the movement of possible contaminants through that groundwater from outside sources. We will also follow the procedures of engineers as they identify and analyze existing contamination of water sources in order to produce high-quality drinking water.

Lesson Background and Concepts for Teachers

Where is the Earth's water located?

Water is found everywhere on the Earth and in the atmosphere in the form of ice, liquid and vapor. Some interesting water facts:

• 97.24% of the Earth's water is found in the salty oceans.

• 2.14% is found in icecaps and glaciers.

• 0.02% of water is found in inland seas and lakes.

• 0.61% of the Earth's water is found underground in aquifers and soils.

Of all the water on Earth, 99.7% of that water is unusable by humans. Only 0.3% of Earth's water is utilized by humans for drinking, washing, cooking and other daily routines (ga.water.usgs.gov/edu/earthwherewater.html ).

What is drinking water?

Drinking water is generally clean in the US because of strict drinking water quality standards. Although drinking water standards regulate the water that comes from our tap, these standards may vary due to the water source and treatment methods. It is important to regulate drinking water because many contaminants occur naturally in waterways. There is no such thing as completely "pure water."

Drinking water comes from many different sources. One large source is surface water, such as lakes, rivers and reservoirs. If no surface water source exists near your community, then your water may comes from an underground water source such as an aquifer. Wells often tap into the natural aquifers that exist below the surface and run all over the Earth. Aquifers can be very small or many miles long. It is important to consider how your source of drinking water is affected by acts of nature and humans. It is not just what happens in the lake, reservoir or well, but what happens over the whole watershed (as was discussed in Lesson 3, An Underground River).

Drinking water directly from a well or surface source can be risky because that source may already have contaminants present. Some compounds in water may be harmful to the organisms that use that water source. These compounds can be naturally occurring — such as metals or minerals from rock erosion, or human-induced — such as fertilizer run-off, factory discharges or dissolved pharmaceuticals. Water dissolves or absorbs whatever it comes in contact with, and this can be dangerous if the substances are harmful.

Water contamination can negatively affect the organisms that come in contact with it. The affects can be acute or cause illness and death. Microbial organisms and large chemical spills in drinking water can cause acute affects. Contaminants can also cause chronic effects in humans, which occur over time after drinking water with dangerous levels of contaminants. Some examples of chronic effects are: cancer, liver and kidney problems. These are most often due to chemical spills, high levels of minerals and other toxins.

Why do engineers care about drinking water?

Environmental engineers are concerned about making drinking water safe for citizens. They determine what contaminants are in the water that may harm people, other species or the environment. They determine the contaminant levels, sources and effects. They monitor industrial and commercial inputs to watersheds as well as natural changes in the watershed from temperatures and time. If industrial inputs are present, engineers track the sources upstream and hold the company responsible for what they are dumping. Engineers use this information to create municipal water treatment plants that remove harmful contaminants from the water. They also take into consideration the water taste. Engineers must be able to design and create a safe water product that tastes and smells acceptable so people will use it. All of these factors are considered when designing a drinking water treatment or remediation system.

What is a water table?

A water table is the surface that divides the vadose zone and the saturated zone of the Earth's crust. The vadose zone is the zone that is exposed to the atmosphere with pore spaces between the individual grains of soil filled mostly with air. The saturated zone is the zone below the water table where the pore spaces of the soil are filled mostly with water. The water table moves up and down with variations in weather, temperature, and precipitation. Because the topography of the Earth's surface is variable, the water table can produce features such as rivers, wetlands, and lakes in low valleys. These water features then change directly with the changing level of the water table.

What is groundwater?

Groundwater is the water source that comes from aquifers below the Earth's surface. These are underground water-bearing sections of permeable rock, sand or gravel. About 20% of water used by people comes from groundwater. Mostly, groundwater sources are used in areas that have few fresh lakes and streams.

The amount of groundwater being used in the US for personal and commercial uses has increased since the 1950s. For the 43 million Americans who supply their own water at home, 99% of them use groundwater well sources. The groundwater supply is tapped into by digging or drilling water wells.

Why do engineers care about groundwater?

Environmental engineers spend much time studying groundwater. They make models of groundwater flow to determine which communities can use different aquifers for their water supply. They demonstrate how groundwater moves so they can determine how contaminants spread underground from industrial spills and landfill leaching. They analyze the physical properties of the groundwater to determine how safe it is and how it can be used. Engineers dig wells and tap into this water resource. Water levels in the well do not always remain constant, but change due to seasonal temperatures and precipitation. Engineers design pumps that accommodate changes in water levels to move water out of wells at constant rates, yet not completely deplete the sources; otherwise, if a water level falls below the pump, the well will only pump air, and it will go dry. Only 20% of our water supply comes from groundwater; however, more groundwater exists on the Earth than the amount of water in lakes and streams. It is important for engineers to be able to utilize groundwater sources in places of increasing temperatures due to global climate change and decreasing surface fresh water supplies.

It is important for citizens to understand just how easily (even if accidentally) they can contribute to the contaminants in drinking water and what treatment can be done to counteract these harmful effects. People can learn how to help engineers protect our natural water sources by being aware of everything they place or pour on the Earth's surface because it may end up in our drinking water.