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.
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
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.
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.