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Ground Water
Below the Surface
It is an Interesting fact that Earth has
forty times more water underground than is found in lakes, rivers, and
streams as surfacewater.
Ground water is a result of precipitation falling on porous ground where
spaces between the soil particles allows water to
seep and then flow beneath Earth's surface.
Ground water is found under the Earth's surface
within the Zone of Saturation. The zone of saturation is a layer of
porous fractured rock, sands, and gravels that become saturated with water.
The upper layer of the zone of saturation is also called the water table.
Within the zone of saturation is an area where
water can be delivered to the surface.
This area is called an aquifer. Ground water is held in these aquifers
which become so saturated that the water can be pumped out onto the
surface.
Copyright 2002 by
TASA Graphics Arts, Inc.
Geologists have identified two types of aquifers.
The first type of aquifer is called a Confined Aquifer that has an
impermeable Aquitard. The aquitard covers the aquifer with a confining layer of
earth material such as: clay, shale, and igneous or metamorphic rocks.
The second type of aquifer is called an Unconfined
Aquifer where there is no impermeable layer restricting the upper
surface of the zone of saturation. Water can be delivered to the surface
from an unconfined aquifer.
The amount of water in an aquifer depends on
several factors.
Porosity and Permeability
Porosity is how much space is available
between the fractured rocks and soil where water might saturate the area.
For example loosely packed soil can hold more water than tightly packed
soil.
Permeability is how well water flows through
the rock and soil. Ground water is primarily replenished by precipitation.
In areas where too much real estate development occurs, it would be
impossible to replenish because the soils are covered with concrete and
asphalt.
A spring can occur when ground water seeps out of
the ground and becomes surface water.
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