Barrons AP Environmental Science

with    water.

■ WATER PERMEABILITY—the    ability of  a   material    to  allow   the passage of

water   through rocks.  Permeable   materials,  such    as  gravel  and sand,   allow

water   to  move    quickly through them,   whereas impermeable materials,

such    as  clay,   don’t   allow   water   to  flow    freely.

■ WATER TABLE—the   level   below   which   the ground  is  saturated   with    water.

Figure  3.2 A   typical aquifer

CASE STUDY

OGALLALA AQUIFER: The Ogallala Aquifer is located in the central
United States. It is one of the world’s largest aquifers, but it is being rapidly
depleted by growing municipal and agricultural use. This huge aquifer, which
underlies portions of eight states, contains water from the time of the last
glaciation (12,000–1.2 million years ago). Annual recharge, in the more arid
parts of the aquifer, is estimated to total only about 10% of annual
withdrawals. The biggest users of water from aquifers include agricultural
irrigation and oil, natural gas, and coal extraction.