Aquifer
What Is an Aquifer?
One of our most valuable resources is the water beneath our feet. Most of the time you can't even see it, and you may not even know it is there. Water (not groundwater) is held by molecular attraction and surrounds the surfaces of rock particles.
Different kinds of rocks have different porosity and permeability characteristics. Because of this, water does not move around the same way in all rocks. When water-bearing rocks readily transmit water to wells and springs, they are called aquifers. Wells can be drilled into the aquifers and water can be pumped out. Precipitation eventually adds water into the porous rock of the aquifer, which is known as recharging. The rate of recharge is not the same for all aquifers, though, and that must be considered when pumping water from a well. Pumping too much water too fast can draw down the water in an aquifer and may eventually cause a well to yield less and less water or even run dry. In fact, pumping your well too fast can even cause your neighbor's well to run dry if you both are pumping from the same aquifer.
Sometimes the porous rock layers become tilted in the Earth. There might be a confining layer of less porous rock both above and below the porous layer. This is an example of a confined aquifer. In this case, the rocks surrounding the aquifer confine the pressure in the porous rock and its water. If a well is drilled into the "pressurized" aquifer, the internal pressure might (depending on the ability of the rock to transport water) be enough to push the water up the well and up to the surface without the aid of a pump. Water can even flow completely out of the well. This type is called an artesian well. The pressure of water from an artesian well can be quite dramatic!
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Water Facts
Some water trivia facts are available at http://www.epa.gov/ogwdw/kids/trivia.pdf.
An information sheet entitled "Water Facts of Life" can be found at http://www.epa.gov/ogwdw/kids/facts.pdf.
A fact sheet, called "Be Hydro-Logical," that gives suggestions for how to save water is available at http://www.epa.gov/ogwdw/kids/logical.pdf.
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Aquifer Vocabulary
(From Perdue University)
Artesian Aquifer -- an aquifer that has pressure built up inside. This pressure is the result of the recharge area of the aquifer being at a higher level than the rest of the aquifer region. The force of gravity pulls the higher water down, which creates extra pressure inside the aquifer. This is why artesian wells flow by themselves; the pressure forces the water out of the well.
Confining Bed -- a layer of ground that resists water penetration. This layer is typically finer textured and denser than the above layers of soil. Confining beds can keep water from seeping to unreachable depths but can also prevent water from reaching aquifers.
Consolidated Rock -- rock that contains very few holes or cracks for water to get through. An example of unconsolidated rock is gravel. Consolidated rock can serve as a confining bed.
Flowing Artesian Well -- a well that has penetrated into an artesian aquifer. Artesian aquifers have pressure built up within themselves. This pressure results from a portion of the aquifer being at a higher elevation as shown in the figure. The pressure is released when a well is bored into it. This causes the well to flow spontaneously.
Nonflowing Artesian Well -- a nonflowing artesian well occurs when the pressure is not great enough to force the water out of the well. In this diagram, this is apparent because the flowing artesian well is at a lower elevation than the non-flowing artesian well
Recharge Area -- an area that allows water to enter the aquifer. It is particularly vulnerable to any pollutants that could be in the water. Also, if pavement is constructed over the recharge area, less water can enter the aquifer. This could mean a water shortage to those people using the groundwater from the aquifer.
Spring -- occurs when the water table is higher than the ground surface. Pressure forces the water out of the land at a weak point that creates the spring.
Surface Water Stream or Pond -- caused by a high water table. Also, a high water table can result from a stream and pond in that area.
Water Table -- the level at which the water stays. It is the very top of the zone of saturation. A few centimeters above this level water can also be found due to capillary action. In the presence of a pumping well, the water table will drop around the well. This is called drawdown. Under some conditions, a perched water table may exist. This occurs when the water percolation is interrupted by another confining layer above the "main" one.
Water Table Aquifer -- an aquifer that supports the water table. The top limit to this aquifer is the water table itself.
Water Table Well -- a water table well is a well that only extends down into the water table aquifer.
The U.S. Department of Energy's Office of Environmental Management also has a glossary at http://www.em.doe.gov/soda/gloss.html.
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Aquifer Activities
AQUIFER ACTIVITY NO. 1
TITLE: DOES IT HOLD WATER?
PURPOSE: Examine the effect of different types of soil on the holding ability of water.
BACKGROUND INFORMATION
Describe porosity
MATERIALS
Soil samples: large grain gravel, fine grain gravel, sand, clay
Graduated cylinder
PROCEDURE
- Measure 200 ml to mark a line in each cup. Pour water into the cup, measure 200 ml on the side of the cup, pour out the water, let dry. The students will know how high to fill the cups with different types of soil. Do this before the experiment and have dry soil cups ready.
- Fill each cup with the soil types: sand, clay, large grain gravel, and fine grain gravel.
- Fill the graduate cylinder to the top. Record how much water is in the graduated cylinder. Slowly pour the water into the first cup. Let the water seep through the sand. Slowly add more water until a small layer is visible on the surface of the sand.
- Find the amount of water held by the sand by subtracting the amount that is left in the graduated cylinder from the total amount of the cylinder. Record this amount in the data sheet below.
- Repeat with each of the other cups: clay, large grain gravel and small grain gravel.
Data Sheet:
1. Find the porosity of each of the soils. Use the formula to find the porosity and place this on the data sheet.
FORMULA: amount of water/the total amount of soil x 100 = _____%
2. Record the porosity on the data sheet.
QUESTIONS
- What can you conclude about the porosity of the four types of soil?
- Why can some soils hold more water?
- How does this experiment relate to an aquifer found in your state?
EXTENSIONS
- The school grounds can be tested for porosity. What region is your school located in?
- How was it formed?
- How can an aquifer system become contaminated?
- What would be the source of the contamination?
AQUIFER ACTIVITY NO. 2
TITLE: BUILD YOUR OWN AQUIFER
This activity at http://www.epa.gov/ogwdw/kids/aquifer.pdf is from the U.S. Environmental Protection Agency's Drinking Water for Kids Web page. This activity illustrates how water is stored in an aquifer, how groundwater can become contaminated, and how this contamination ends up in well water. Several outstanding activities about the water management cycle are listed by grade level at http://www.epa.gov/ogwdw/kids/exper.html.
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Aquifer Links
Office of Environmental Management, U.S. Department of Energy
http://www.em.doe.gov/soda/
Here are 11 activities that help students better understand concepts relating to groundwater, aquifers, and hydrology.
U.S. Geological Survey
http://interactive2.usgs.gov/learningweb/students/homework_hydrology.asp
This Web page includes featured sites about hydrology, including Water Science for Schools, Groundwater Basics, and Glacier FAQs.
U.S. Geological Survey
http://ga.water.usgs.gov/edu/earthgwaquifer.html
The USGS provides an excellent description of an aquifer. For more information on aquifers by rock type (unconsolidated, sandstone, sandstone and carbonate, semiconsolidated, carbonate-rock, and volcanic), go to http://capp.water.usgs.gov/aquiferBasics/index.html To learn about all kinds of water, visit the USGS Water Science for Schools web site at http://ga.water.usgs.gov/edu/. Here there is information on many aspects of water, along with pictures, data, maps, and an interactive center where you can give opinions and test your water knowledge.
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