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What Is Ground Water And How Can It Be Polluted?
Ground water is a resource found under the earth’s surface. Most ground
water comes from rain and melting snow soaking into the ground. Water
fills the spaces between rocks and soils, making an “aquifer”. (See Watershed
Graphic.) About half of our nation’s drinking water comes from ground
water. Most is supplied through public drinking water systems. But many
families rely on private, household wells and use ground water as their
source of fresh water.
Ground water — its depth from the surface, quality for drinking water,
and chance of being polluted — varies from place to place. Generally,
the deeper the well, the better the ground water. The amount of new water
flowing into the area also affects ground water quality.
Ground water may contain some natural impurities or contaminants, even
with no human activity or pollution. Natural contaminants can come from
many conditions in the watershed or in the ground. Water moving through
underground rocks and soils may pick up magnesium, calcium and chlorides.
Some ground water naturally contains dissolved elements such as arsenic,
boron, selenium, or radon, a gas formed by the natural breakdown of radioactive
uranium in soil. Whether these natural contaminants are health problems
depends on the amount of the substance present.
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A “watershed” is the land area where water soaks through the earth
filling an underground water supply or aquifer. It is also called
a recharge area. The “water table” is the line below which the ground
is saturated or filled with water and available for pumping. The water
table will fall during dry seasons. A well can pump water from either
the saturated zone or an aquifer. Wells must be deep enough to remain
in the saturated zone. |
In addition to natural contaminants, ground water is often polluted by
human activities such as
- Improper use of fertilizers, animal manures, herbicides, insecticides,
and pesticides
- Improperly built or poorly located and/or maintained septic systems
for household wastewater
- Leaking or abandoned underground storage tanks and piping
- Storm-water drains that discharge chemicals to ground water
- Improper disposal or storage of wastes
- Chemical spills at local industrial sites
These problems are discussed in greater detail later in this brochure.
Suburban growth is bringing businesses, factories and industry (and potential
sources of pollution) into once rural areas where families often rely
on household wells. Growth is also pushing new home developments onto
the edge of rural and agricultural areas. Often municipal water and sewer
lines do not extend to these areas. Many new houses rely on wells and
septic tanks. But the people buying them may not have any experience using
these systems.
Most U.S. ground water is safe for human use. However, ground water contamination
has been found in all 50 states, so well owners have reason to be vigilant
in protecting their water supplies. Well owners need to be aware of potential
health problems. They need to test their water regularly and maintain
their wells to safeguard their families’ drinking water.
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The hydrologic cycle is the natural process of rain and snow
falling to earth and evaporating back to form clouds and fall again.
The water falling to earth flows into streams, rivers, lakes and
into the soil collecting to form ground water.
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