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The area within which the potentiometric surface is lowered by withdrawal or raised by injection, of water through a well

A geologic unit that is saturated and sufficiently permeable to transmit significant economic quantities of water to wells and springs

The lowest par of the zone of aeration, immediately above the water table, where water is under pressure that is less than atmospheric pressure

A depression in the potentiometric surface of ground water that has the shape of an inverted cone and develops around a well from which water is being withdrawn. It defines the area of influence of a well

An aquifer overlain by a confining layer of low permeability

A unit of intrinsic permeability = 9.87x10^-9cm²

The basic equation describing ground water flow: Q=KiA

An area where subsurface water is dischanged to land, bodies of water or the atmosphere

The amount the water level in a well is lowered due to withdrawal of water

The percentage of the total volume of a soil or rock that consists of interconnected pore space. The term is sometimes used analogously to specifi yield.

The quantity of water held by the soil or rock against the pull of gravity. Field capacity is dependent on the length of time the soil or rock has been undergoing gravity drainage, while specific retention is not

Two-dimensional representation of flow lines and equipotentials

A measure of the potential energy of a fluid at any given point with respec to a given datum. In practice, it is the elevation to which water rises at a given point as a result of reservoir pressure

The capacity of a porous medium to transmit water. The rate at which fluid can move through a permeable medium depends on properties of the fluid (viscosity and specific weight) and properties of the medium (intrinsic permeablity)

Rate of change in the total head per unity of distance of flow in a given direction

A property of the porous medium that measures the relative ease with which a fluid can be transmitted through it under a hydraulic gradient. Dependent on pore size and measured in Darcys

Water that is derived directly from magma and is though to have come to the Earth's surface for the first time

A unit of hydraulic conductivity in gpd/ft². Rate of flow in gallons per day through a cross section of 1 ft² under a unity of hydraulic gradient at 60^oF

An aquifer test in which two inflatable seals (or packers) are set in an open borehole to prevent movement of ground water in the test section while the permeability of the isolated rock is determined

Unconfied ground water separated from an underlying body of ground water by an unsaturated zone

A test made by digging a hole, filling it with water, and meausring the rate of decline of the water level. This is test is used to determine the soil suitability for sewage disposal systems

The property of a porous rock or soil for transmitting a fluid. It measures the relative ease of flow under unequal pressure

The precentage of the bulk volume of a rock or soil that is occupied by void space

A surface that represents the total head of ground water and is defined by the level to which water will rise in a well

A test made by pumping a well for a period of time and observing the change in hydraulic head in the aquifer

An area where water infiltrates downward into the saturated zone

That part of preciptitation appearing in surface streams

An aquifer test made either by pouring a small charge of water into a well or by removing a slug of water from the well. The removal of water from the well is also called a bail-down test

Ratio of the volume of water a soil or rock can retain against gravity drainage to the total vouume of the soil or rock, usually stated as a percentage

Amount of water per unit volume of a saturated formation that is stored or expelled from storage due to compressibility of mineral skeleton and pore water per unit change in head. Units are ft^-1

Ratio of the volume of water that drains from a saturated soil or rock due to gravity to the total voume of soil or rock, stated as a percentage

Volume of water that a permeable unit releases from or takes into storage per unit surface area of the aquifer of the aquifer per unit change in head. In an unconfined aquifer, storage = specific yield

The capacity of an aquifer to transmit water of the prevailing kinematic viscosity. T=Kb, where b = saturated thickness of the aquifer. Dimensions are gpd/ft or ft²/day

An aquifer having a water table

Ground water that flows beneath the bed or alluvial plain of a surface stream, especially in arid regions

A subsurface zone containing water under pressure that is less tha atmospheric pressure. A synonym of vadose zone is unsaturated zone

The surface within unconfined ground water at which the hydraulic pressure is equal to atmospheric pressure

The region drained by a stream or body of water, or a drainage divide

The ratio in percent of theoretical drawdown to actual drawdown measured in a well