Page 342 - Laboratory Manual in Physical Geology

ACTIVITY just as a homeowner withdraws water from a water well.
After you drank some of the drink, the cup contained
12.1 Groundwater Inquiry both a zone of saturation (water and ice in the bottom of
the cup) and a zone of aeration (ice and mostly air in the
THINK | How does water behave underground? upper part of the cup). The boundary between these two
zones was a water table. In order to continue drinking the
About It
liquid, you had to be sure that the bottom of your straw
was within the zone of saturation, below the water table.
OBJECTIVE Experiment with water to determine its Otherwise, sucking on the straw produced only a slurping

behavior in confined and unconfined spaces and in sound, and you obtained mostly air. Natural water wells

relation to shale and sandstone. work the same way. The wells must be drilled or dug to a
PROCEDURES point below the water table (within the zone of saturation),
so that water can flow or be pumped out of the ground.
1. Before you begin , do not look up defi nitions and
information. Use your current knowledge, and
complete the worksheet with your current level of Porosity and Permeability
ability. Also, this is what you will need to do the The volume of void space (space filled with water or air) in

activity: sediment or bedrock is termed porosity. The larger the voids,
and the greater their number, the higher is the porosity. If
____ empty plastic drink bottle (2 liter), water, tape
____ nail, drill, or other object that can be used to void spaces are interconnected, then fluids (water and air)
safely make small holes in a plastic bottle can migrate through them (from space to space), and the
____ Activity 12.1 Worksheet (p. 321 ) and pencil rock or sediment is said to be permeable. Sponges and paper
towels are household items that are permeable, because
2. Complete the worksheet in a way that makes liquids easily flow into and through them. Plastic and glass
sense to you. are impermeable materials, so they are used to contain fluids.
3. After you complete the worksheet , be prepared
to discuss your observations and ideas with others. Aquifers
Permeable bedrock materials make good aquifers , or rock
strata that conduct water. Some examples are sandstones
and limestones. Impermeable bedrock materials prevent the
ACTIVITY flow of water and are called confining beds (or aquitards ).

Some examples are layers of clay, mudstone, shale, or dense
12.2 Karst Processes and igneous and metamorphic rock. But how does groundwater
Topography move through aquifers?
Confined aquifers are sandwiched between two confin-
THINK | What is karst topography and how ing beds, the groundwater fills them from confining bed to
confining bed, so there is no water table. The weight of the
About It does water flow beneath it? groundwater (being pulled downward by gravity) in a con-
fined space creates water pressure, like the pressure inside of
OBJECTIVE Explore and evaluate the topographic a garden hose or kitchen sink faucet. If a confined aquifer is

features, groundwater movements, and hazards penetrated by a well, then water flows naturally from the well.
associated with karst topography. When aquifers are not confined (i.e., they are unconfined

aquifers ), the groundwater establishes a water table just
PROCEDURES
beneath the surface of the land ( FIGURE 12.1 ). For this reason,

1. Before you begin , read the Introduction and Caves unconfined aquifers are also called water table aquifers. If an
and Karst below. Also, this is what you will need :
unconfined aquifer is penetrated by a well, then the water
____ calculator, colored pencils must be pumped from the ground using a submersible pump
____ Activity 12.2 Worksheet (p. 323 ) and pencil lowered into the well on a cable. An electric line runs from
2. Then follow your instructor’s directions for the top of the well to the submersible pump, and a water
completing the worksheet. hose runs from the submersible pump to the top of the well.

Hydraulic Gradient
Groundwater in an unconfined (water table) aquifer is
Recall the last time that you consumed a drink from a pulled down by gravity and spreads out through the ground
fast-food restaurant (a paper cup containing ice and liquid until it forms the water table surface (such as the one in
that you drink using a plastic straw). The mixture of ice the drink cup full of crushed ice described previously).
and liquid (no air) at the bottom of the cup was a zone of You can see the water table where it leaves the ground and
saturation, and your straw was a well. Each time you sucked becomes the level surface of a lake ( FIGURE 12.1A ) or springs
on the straw, you withdrew liquid from the drink container flowing from a hillside. However, because groundwater is

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