find fresh liquid water is under the Earth’s surface, in a form calledgroundwater(Figure
13.20). Water from the surface seeps downward into the ground through tiny spaces or pores
in the rock. At some point, though, it hits a layer of rock that no longer has pores, which
stops the water from traveling downward. This rock is calledimpermeablebecause the
water can no longer pass through it. The upper surface of the groundwater is called the
water table.The water table will fall when there has been little rain in an area for a long
time. The water table will also rise when it rains steadily for a long time. It is important
to know how deep beneath the surface the water table is for anyone who intends to dig into
the surface or make a well. Because groundwater involves interaction between the Earth and
the water, the study of groundwater is calledhydrogeology.
Figure 13.20: Groundwater is found beneath the solid surface. Notice that the water table
roughly mirrors the slope of the land’s surface. A well penetrates the water table. ( 9 )
Aquifers
Large collections of groundwater can be found inaquifers(Figure13.21). Aquifers are
large regions of sediment or rock that can hold significant amounts of groundwater. Aquifers
can be large, sustainable water resources when water pumped out of aquifers is replenished
by the water cycle. However, some aquifers are overused; people pump out more water
than can be replaced. As the water is pumped out, the water table slowly falls, requiring
people to spend more energy pumping out the water from greater depths. In addition, some
wells may go completely dry if they are not deep enough to reach into the lowered water
table. Draining aquifers can lead to the ground sinking, sometimes under houses and other