The Phreatic Zone

PHREATIC ZONE - The zone below and including the water table in which all pore spaces or fissures are totally filled with water. Also referred to as the saturated zone.

AQUIFER - A saturated geological unit (eg. sands, gravels, fractured rock) which can yield water to wells at a sufficient rate to support a well.

SEMI-CONFINED AQUIFER - A semi-confined (leaky) aquifer is a completely saturated aquifer overlain by a semi-impervious layer and underlain by a impervious layer. Lowering of the potentiometric head in a leaky aquifer by pumping will generate a vertical flow of water from the semi-pervious layer into the pumped aquifer.

CONFINED AQUIFER - A confined aquifer is a fully saturated aquifer whose upper and lower boundaries are impervious geologic units. Water is held under pressure and the water level in wells stands above the top of the aquifer. Completely impervious layers rarely exist in nature and hence truly confined aquifers are relatively rare.

UNCONFINED AQUIFER - An aquifer whose upper boundary is defined by the water table (water is at atmospheric pressure). Water usually saturates only part of the geologic unit and there is no upper confining layer. Also called a “water table aquifer”.

GROUNDWATER FLOW SYSTEM - The total system which describes the movement of water in the subsurface from the point where it enters the ground to where it leaves. Water moves in the direction of decreasing pressure that may be upward in some localities.

HYDROGEOLOGY - The subject dealing with the occurrence, characterization and movement of water below the earth’s surface.

HYDROLOGICAL CYCLE - The continuous circulation of moisture and water on earth. The amount of water never changes but its state and position in the cycle does change.

KARST - A carbonate rock terrain where fractures have been enlarged by chemical solution or physical erosion.

KARST WINDOW - An opening to the Aquifer i.e Mexico - Cenote, U.S - Sink Hole or France - Gouffer.

SORPTION - The attachment of dissolved ions to rock minerals, generally by electromagnetic bonding forces.

UNSATURATED ZONE - The zone above the water table in which soil pores or fissures are less than totally saturated. It is also called the vadose zone or the zone or aeration.

WATER TABLE - The top of the zone in which all pore spaces or fissures are totally filled with water.

TALUS CONE - Debris from the collapsed sink hole, directly under the Karst window