What are Aquifers?

A zone of material capable of supplying ground water at a useful rate from a well is called an aquifer. Gravel, sand, soils, and fractured sandstone, as well as granite and metamorphic rocks with high porosity due to connected open fractures, are good aquifers if ground water is present.

A zone of earth material that will hold water but not transmit fast enough to be pumped is called and aquiclude or aquitard. Aquitards often form a confining layer through which little water moves. Clay soils, shale, and igneous or metamorphic rocks with little interconnected porosity and or fractures are likely to form aquitards

An aquifer is called an unconfined aquifer if there is no confining layer restricting the upper surface of the zone of saturation at the water table. If a confining layer is present the aquifer is called a confined aguifer and the water beneath it may be under pressure, forming artesian conditions. Similar to the effect that a water tower that produces water pressure for homes.

Water in artesian systems tends to rise to about the height of the recharge zone (the zone where precipitation infiltrates the surface to move down to the ground water system, creating an artesian well.

Ground water recharge is any process that adds water to an aquifer and can be natural infiltration or human induced, like leakage from a broken water line. Ground water discharge is any process that removes ground water from an aquifer. Included is natural discharge from a spring that is present where water flowing in an aquifer intersects the surface of the earth. Spring discharge can form the beginning of a stream or river.

Ground water discharge also occurs when water is pumped from a well. Both confined and unconfined aquifers many be found in the same area.

When water is pumped from a well, a cone of depression forms in the water table or artesian pressure surface. A large cone of depression can alter the direction in which ground water moves within an area. Overpumping of an aquifer causes the water level to lower continuously over time, which necessitates the lowering of pump settings or drilling deeper.

next 1 2