Aquifer

An aquifer is a permeable geological formation that stores and transmits groundwater in quantities sufficient to supply wells or springs.

Groundwater: Water held beneath Earth's surface in the pores and fractures of soil and rock. Aquifers are formations through which groundwater is stored and transmitted.
Aquifer test: A field test that uses pumping and water-level responses to estimate aquifer properties. Tests reveal how transmissive and capacious a particular aquifer is.
Well: A shaft or borehole constructed to access groundwater. Wells draw water from aquifers for domestic, agricultural, and industrial use.
Ogallala Aquifer: A vast aquifer beneath parts of eight Great Plains states in the United States. Its intensive irrigation use illustrates the limits of groundwater-dependent agriculture.
Aquitard: A geological layer that transmits groundwater slowly enough to impede flow between aquifers. Unlike an aquifer, it restricts rather than readily supplies groundwater flow.
Porosity: The proportion of a material's volume occupied by pores or voids. Pore space determines how much water an aquifer can store.
Unconfined aquifer: An aquifer whose upper boundary is the water table and is not sealed by a confining layer. Its water table responds directly to recharge and groundwater withdrawals.
Groundwater pumping: The extraction of groundwater by pumps installed in wells. Pumping lowers groundwater levels and can alter aquifer flow.
North China Plain: A densely populated and intensively farmed region of eastern China. Heavy groundwater withdrawals there have contributed to declining water tables and subsidence.
Aquiclude: A geological formation that stores water but transmits little or none under ordinary conditions. It can hold water without providing the useful transmission that defines an aquifer.

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