The Well That Can't Run Dry
Author: Robert A. Linton
A well is a hole sunk in the ground to bring water, oil, gas, brine, or other fluids to the surface. Although all types of wells are important today, we will mainly discuss water wells. The story of the spread of civilization is closely connected with the discovery that water could be found underground.
Early man was dependent upon rivers, lakes, and springs for his water supply until he learned, probably quite by accident, that he could find water in many places by digging a hole in the ground. The first wells were simply crude holes. But man soon found how to make better wells, which would produce more water over longer periods of time.
Wells were lined with stone or wood, and later, brick, to keep the walls from caving in. These linings were purposely made pervious (full of tiny holes), so that the water could enter the well but the soil and sand would be held back.
The water tapped by wells is called ground water. When rain or snow falls on the surface of the ground, some of it flows into streams and rivers and collects in lakes. (This water is called surface water.) Some evaporates and returns directly to the atmosphere. Some is used by growing plants. The rest seeps downward through the earth until it collects in crevices of rocks or pockets of water-soaked earth material. The top of the water-soaked material is called the water table.
Groundwater moves slowly through the earth materials, always seeking a lower level. Water seeps through the earth in two ways. It soaks into loose sand or mixtures of sand and gravel until all the spaces between the grains are filled. Rocks with cracks and other breaks also allow water to pass through. These earth materials through which water can move are called aquifers. (“Aquifer” is from the Latin for “water carrier.”)
In some places more than one aquifer is found under the surface. A sand-and-gravel aquifer may lie directly on a hard-rock aquifer, or the two acquifers may be separated by materials through which water cannot move or moves very, very slowly.
The water in the lower aquifer may be trapped under pressure. When a well is drilled, the pressure may force the water in the well higher than the top of the aquifer. Wells drilled in this type of ground structure are called artesian wells. If the pressure is great enough, the water actually flows out of the well above ground. This type of well is known as a flowing artesian well.