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There are two types of aquifers: confined and unconfined. In confined aquifers, there is an overbearing layer called an aquitard, which contains impermeable materials through which groundwater cannot be extracted. In unconfined aquifers, there is no aquitard, and groundwater can be freely extracted from the surface.
An aquifer in the same geologic unit may be confined in one area and unconfined in another. Unconfined aquifers are sometimes also called water table or phreatic aquifers, because their upper boundary is the water table or phreatic surface (see Biscayne Aquifer). Typically (but not always) the shallowest aquifer at a given location is ...
Well core data indicate that the Santa Clara Valley Aquifer consists of between four and six different water-bearing units. The aquifer is composed of both confined and unconfined units. Water-bearing units are generally coarse-grained and separated by relatively fine-grained units.
California aquifers, excerpted from map in Ground Water Atlas of the United States (USGS, 2000): Lavender is "other" for "rocks that generally yield less than 10 gal/min to wells"; dark green-blue (3) are the California coastal basin aquifers, bright-turquoise blue (7) is the Central Valley aquifer system, flat cobalt-blue (1) down south is Basin and Range aquifers
For a confined aquifer or aquitard, storativity is the vertically integrated specific storage value. Specific storage is the volume of water released from one unit volume of the aquifer under one unit decline in head. This is related to both the compressibility of the aquifer and the compressibility of the water itself.
California passed its landmark groundwater law in 2014. The goals of sustainable management remain a long way off. Despite California groundwater law, aquifers keep dropping in a 'race to the bottom'
California's groundwater levels rose significantly in 2023, one of the wettest years in decades. State officials say efforts to replenish aquifers helped.
Aquifers of the United States Withdrawal rates from the Ogallala Aquifer.. This is a list of some aquifers in the United States.. Map of major US aquifers by rock type. An aquifer is a geologic formation, a group of formations, or a part of a formation that contains sufficient saturated permeable material to yield significant quantities of water to groundwater wells and springs.