Jason Winslow, age 14, of Dayton, Ohio, for his question:
WHAT IS GROUND WATER?
Ground water is water that is held beneath the surface of the earth. It is usually pure and cool and is one of the best sources of drinking water for man's use.
When a well is drilled through the ground, it passes through layers containing different amounts of water. In the top layer of soil, called the vadose zone, soil pores or spaces in the soil contain both air and water.
Ground water begins to enter the well when it reaches the zone of saturation where soil pores are completely filled with water.
The water table is the upper surface of the zone of saturation. The zone of saturation may extend deep into the earth but most ground water is found in the first 3,000 feet. At depths below 3,000 feet, the pressure of the earth above packs the soil or rock so tightly there is little space for water.
When the water table meets the surface of the ground, ground water flows openly in springs and streams. It may also form lakes or water holes.
Under normal conditions, the amount of water in the ground remains fairly constant. But when man pumps water from the ground faster than it can be replaced naturally, the water table drops. To replace lost water rain water can be pumped into wells or spread in areas where it can seep into the ground easily.
There are three types of ground water: meteoric water, juvenile water and connate water.
Meteoric water makes up most of the 2 million cubic miles of ground water in the earth. It filters through the soil after a rain or seeps into the ground from rivers and lakes.
Connate water is salt water that was trapped in rocks when the rocks were laid down in ancient oceans.
An artesian well is a well in which water rises above the level of water held beneath the earth. If the water rises above the surface of the ground, the well is a flowing artesian well.
Artesian wells are found where an aquifer or water bearing layer of earth is surrounded by dense clay or rock slopes downward. The water is trapped because it cannot pass through the clay or rock and gravity creates pressure on it as it flows downward. When a well breaks through the dense layer above the aquifer, the pressure forces the water up into the well.
A famous artesian aquifer, the Dakota sandstone, carries water from the Rocky Mountains east to South Dakota.
Some artesian wells drilled in Dakota sandstone shot water more than 200 feet in the air when first opened.
The name artesian comes from Artois province in France, where such wells were first discovered about 1100.