Get the Ground Water Picture
Out of sight, out of mind. Because ground water is hidden
below Earth’s surface, many people do not have a visible reference
point as they when they look at water in lakes or rivers. However,
because ground water is so widely used as a source of drinking
water, nearly everyone is likely to drink ground water every day.
Ground water is one of Earth’s most valuable natural resources.
The water stored in the pores, cracks, and openings of subsurface
rock material is ground water. Wells dug by hand or machine have
been used throughout history to retrieve water from the ground.
Scientists use the word aquifer to describe an underground formation
that is capable of storing and transmitting water.
Aquifers come in all shapes and sizes. Some aquifers may
cover hundreds of square miles and be hundreds of feet thick, while
others may only cover a few square miles and be a few feet thick.
Water quality and quantity vary from aquifer to aquifer and sometimes
within the very same system. Some aquifers can yield millions of
gallons of water per day, while others may only be able to produce
small amounts of water each day. In some area wells might have to
be drilled thousands of feet to reach usable water, while in other
areas water can be located only a few feet down. One site might
contain several aquifers located at different depths, and another site
might yield little or no ground water.
The age of ground water varies from aquifer to aquifer. For
example, an unconfined surface aquifer might hold water that is only
a few days, weeks, or months old. On the other hand, a deep aquifer
that is covered by one or more impervious layers may contain water
that is hundreds or even thousands of years old.
The rate of movement of ground water varies based on the rock
material in the formation through which the water is moving. After
water percolates down to the water table, it becomes ground water
and starts to move slowly down gradient. Water movement responds
to differences in energy levels. The energies that cause ground
water to flow are expressed as gravitational energy and pressure
energy. These are both forms of mechanical energy. Gravitational
energy comes from the difference in elevation between the recharge
area (where water enters the ground water system) and the
discharge area (where water leaves the system). Pressure energy
(hydraulic head) comes from the weight of overlying water and earth
materials. Ground water moves toward areas of least resistance.
Ground water encountering semi-impervious material, such as clay,
will slow down significantly, when it moves towards an open area,
such as a lake, water’s rate movement will increase.
Hydrogeologists, scientists who study ground water, know that
the above variables exist and that to really “get the ground water
picture” they must drill wells. Wells provide the best method of
learning the physical, hydrologic, and chemical characteristics of an
aquifer. As a well is drilled deeper and deeper into the ground, the
drill passes through different rock formations. The driller records the
exact location of the well, records the depth of each formation, and
collects samples of the rock material penetrated (sandstone, sand,
clay, etc). This data becomes part of the well’s record or well log.
The driller’s record provides valuable information for determining
ground water availability, movement, quantity and quality. The well
driller then caps and seals the well to protect it from contamination.
If hazardous waste, chemicals, heavy metals, oil, etc. collect on
the surface of the ground, rain, or runoff percolating into the soil can
carry these substances into ground water. When hydrogeologists or
water quality specialists analyze the quality of ground water, they
consider land use practices in the watershed and in the vicinity of the
well.
Ground Water Observation
Materials
 4 clear cups
 gravel
 sand
 clay
 water
 stop watch
1. Take three of the cups and carefully poke holes in the bottom of the
container. (a pen will work best)
2. Fill one of the clear cups with gravel, another with sand, and the last
with clay.
3. Make an observation chart on a separate sheet of paper.
a. CLAY
GRAVEL
SAND
4. Fill the remaining cup (no holes) with water.
5. As you slowly pour the water over one of the cups at a time start the
stopwatch. Do this over a sink or a shallow basin.
6. Write down your observations of the water as it moves through the
material.
7. When the water reaches the bottom of the container, write down the
time it took to percolate through the material.
8. Answer the following questions in full sentences:
a. Which container emptied the fastest? Why?
b. Which container emptied the slowest? Why?
c. How would the different materials influence water movement in
natural systems?
Ground Water Picture
1. Get a 1x12 inch strip of white paper.
a. This represents the length of a well that has been dug. You are
going to receive data about the location and types of rock materials
in your well. Then you will transfer that information to your strips
of paper. This will allow you to make a well log.
2. Measure one-inch increments along the paper.
3. Making your well log.
a. You will have to carefully draw and mark each of the different
layers of rock. Do not draw any of the rock layers in blue.
b. Mark the beginning of the water table by making a double
line (dark).
c. Mark the area where the water table ends by a double line.
d. Then color the area where the water can be found blue. Keep
it light enough so you can see the rock layers.
4. Answer the following questions in full sentences:
a. The horizontal scale of the cross section is 1 inch = 1 mile. The
vertical scale is 1 inch = 50 feet.
i. How many miles are horizontally represented in the cross
section (map)?
ii. How many feet are vertically represented in the cross
section?
b. How many feet below the surface is the water table?
c. Imagine a drop of water falling on the surface of your well.
i. Describe the water drop’s movement down the rock column
ii. Which layers would it move the fastest? Explain.
iii. Which layers would it move the slowest? Explain.
iv. At which layer might the water drop’s movement be
restricted? Explain.
v. What pollutants might this drop of water pick up as it filters
through the ground?
vi. Only a very small amount of water would be able to pass
through the clay layer. What they could be the source of
the water beneath the clay level.
5. Assemble your water log with the other lab groups water logs.
6. Observe the assembled water logs and locate the parts of the ground
water system on your Well Log Ground Water Chart. (Use the
definitions below)
7. Observe the assembled water logs and answer the following questions in
full sentences:
a. What direction is the ground water moving in the unconfined
aquifer?
b. What are the water sources for the unconfined aquifer?
c. How long would it take the water in the sandstone formation to
move from Well #1 to Well #15?
d. Now that you know about the land use above the other well sites
and the direction the water travels: What pollutants might this
drop of water pick up as it filters through the ground?
e. Look at the Cone of Depression diagram. A cone of depression
results from water being drawn up the well. Locate one cone of
depression on the Well Log Ground Water Chart.
f. Refer to the Ground Water System (Simplified). What are the
possible sources of water in the confined aquifer portion of your
well?
g. If you had to drill a well, which sites would you consider to be the
most favorable?