Ground Water Glossary

Artesian Aquifer - Aquifer in which ground water is confined under pressure that is significantly greater than atmospheric pressure. Synonym: Confined Aquifer. See also Unconfined Aquifer.

Aquifer - A geologic formation, group of formations, or part of a formation that contains sufficient saturated permeable material to yield significant quantities of water to springs and wells.

Ground water - In the broadest sense, all subsurface water; more commonly that part of the subsurface water in the saturated zone.

Hardness (water) - A property of water that causes the formation of an insoluble residue when the water is used with soap and a scale in vessels in which water has been allowed to evaporate. It is due primarily to the presence of ions of calcium and magnesium. Generally expressed as milligrams per liter as calcium carbonate (CaCO₃). A general hardness scale is:

Description	Milligrams per liter as CaCO3
Soft		0 - 60
Moderately hard		61-120
Hard		121-180
Very hard		More than 180

Molecular Attraction - Attraction produced by or existing between the smallest particle of an element or compound that can exist in the free state and still retain the characteristics of the element or compound.

Permeability - The capacity of a rock for transmitting a fluid; a measure of the relative ease with which a porous medium can transmit a liquid.

Porosity - The ratio of the volume of voids in a rock or soil to the total volume.

Potentiometric surface - An imaginary surface representing the static head of ground water in tighty cased wells that tap a water-bearing rock unit (aquifer); or, in the case of unconfined aquifers, the water table.

Saline water - Water that is considered generally unsuitable for human consumption or for irrigation because of its high content of dissolved solids; generally expressed as milligrams per liter (mg/L) of dissolved solids; seawater is generally considered to contain more than 35,000 mg/L of dissolved solids. A general salinity scale is

	Concentration of dissolved solids, in milligrams per liter
Slightly Saline	1,000 - 3,000
Moderately Saline	3,000 - 10,000
Very Saline	10,000 - 35,000
Brine	More than 35,000

Spring - Area where there is a concentrated discharge of ground water that flows at the ground surface.

Unconfined Aquifer - Aquifer whose upper surface is a water table free to fluctuate.

Unsaturated zone - A subsurface zone above the water table where the pore spaces may contain a combination of air and water.

Water table - The top water surface of an unconfined aquifer at atmospheric pressure.