A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Abandoned Well
A term used when a well's use is permanently discontinued or if it is in a condition that makes it uneconomic to repair. Wells not in use, but which are properly capped may be referred to as out-of-use wells. To prevent the risk of contamination, abandoned wells should be sealed from the bottom up.

Accelerated Erosion
Erosion of soil & sediments at a much more rapid than (geologic) erosion. Usually resulting from land use influences or natural catastrophes that expose soil surfaces, (e.g., fire).

Acidic Water
Acidic water has a pH of less than 7, (which is neutral) and alkaline water has a pH of more than 7. Acid water has more free hydrogen ions (H+) than hydroxyl ions (OH-). Most wetlands have acidic water because of the decaying organic material of wetland vegetation. See also alkaline, pH.

Acre-foot
A measure of water volume, principally used in the western states of the US. An acre-foot (acre-ft) is the volume of water required to cover 1 acre of land (43,560 square feet) to a depth of 1 foot. Equal to 325,851 gallons or 1,233 cubic meters. As a very rough estimate, an acre-foot is often used as a measure of how much water a (western US) family of four might use in one year.

Activated Carbon
Material used in water conditioning. It is very porous and acts as an absorbent for organic matter and some dissolved gases. Homeowners with carbon filters should pay attention to service and maintenance instructions.

Aeration
Process of bringing air into contact with water to remove or reduce unwanted dissolved gases and/or to oxidize dissolved compounds. For example, aeration devices can be effective for removing radon from water.

Air Stripping
The process of removing contaminants from solution in water to solution in air. Air stripping towers are vertical cylindrical air stripping devices are often used in ground water remediation at sites where gasoline has contaminated ground water.

Alignment (well alignment)
A measure of the "vertical straightness" of a well. It is the horizontal distance between the well's actual centerline and the true vertical centerline from the top of the hole. Well alignment is particularly important for line-shaft turbine pumps that have the pump motor at the surface.

Alkaline Water
Water with a pH greater than 7. In typical water analysis alkalinity is represented by carbonates and bicarbonates. See also pH, acid water.

Alkalinity
The capacity of water for neutralizing an acid solution.

Alluvium
Sedimentary deposits of silt, sand, gravel, that have been transported and then deposited by running water, usually a stream or river. Modern alluvial deposits are found in streambeds, river valleys, flood plains, deltas and estuaries Many ancient geological formations are made up of alluvial sediments. Alluvial aquifers are important water sources. See also sand & gravel aquifers, stratified drift.

Anaerobic
A condition of oxygen deficiency found in some saturated soils. Changes of oxygen levels in soils and rock sediments can have important effects on ground water chemistry.

Analytical Model
Computer model that uses mathematical equations as a basis to describe ground water flow.

Anisotropic Aquifer
An aquifer with sediments/ rock structures that result in different vertical and horizontal hydraulic properties. See also isotropic aquifer

Annulus (Annular Space)
The space between a drilled hole and the well casing. Sealing the annulus can reduce the chances of surface contaminants reaching groundwater.

Antecedent
The conditions occurring before a particular hydrologic event. For example antecedent soil moisture conditions prior to a rainfall event will have an influence on infiltration rates.

Appropriation Doctrine
A system of water law used in the western United States under which the right to water is acquired by the user by diverting (pumping) water and applying to a beneficial use. The right to water use is basically "first come first served." Later water users have junior fights compared with the senior rights of the first users.

Aquaculture
Farming of plants and animals that live in water, such as fish, shellfish, and water cress. Usually some aspects of the natural aquatic environment is modified, controlled and managed and may include ponds/ diversion weirs or drilled wells to make aquaculture commercially viable. Many hatcheries and fish farms use wells as their supply source because the water has a constant temperature and chemistry.

Aquatic
Associated with and dependent upon water. For example, aquatic vegetation.

Aqueduct
A pipe, conduit, or channel designed to transport water from a distant remote source, usually by gravity. Part of the water system of ancient Rome was supplied with water conveyed by elaborately engineered aqueducts. Much of the water transferred from north to south in California and other western states is conveyed by aqueducts.

Aquiclude
A saturated rock formation or layer of geologic sediments with low permeability. Aquicludes do not yield significant amounts of water to wells but may be important as water storage zones that release water to more permeable formations.

Aquifer
(1.)The three dimensional sub-surface geometry of a geologic rock formation (or, group of rock formations or part of a formation) that contains ground water in the spaces between sediment grains, in voids, or in fractures. (2.) A geological formation or structure that has the capability to store and/or transmit water to wells and springs. Use of the term aquifer is usually restricted to those water-bearing formations capable of yielding water in sufficient quantity to constitute a usable supply source.
See confined aquifer, unconfined aquifer.

Aquifer Recharge
The process/processes by which water from precipitation (or some other part of the hydrologic system) reaches and hence increments stores of ground water.

Aquifer Test
Hydraulic test of an aquifer based on calculations using data from measurements of ground water level response (drawdown and recovery) to controlled pumping. (Occasionally tests may add water to a well). Aquifer tests typically allow hydrologists to predict the amount of water in an aquifer and the rates at which it may be safely withdrawn.

Aquitard
A geologic formation having very low permeability through which water cannot move.

Area of Influence
The land area overlying the extent of a pumping well's cone of depression.

Arsenic
Arsenic is a semi-metallic element found in many types of rock.
To Purchase Pamphlet #13:Arsenic and Ground Water: Questions, Answers and Solutions

Artesian Aquifers
Artesian aquifers (confined aquifers) occur where overlying impermeable rock layers "trap" ground water under pressure. Depending on geology and topography, a single aquifer may be artesian (confined) in one place and unconfined in another.

Artesian Water
Ground water that is under pressure when tapped by a well and is able to rise above the level at which it is first encountered. It may or may not flow out at ground level. The pressure in such an aquifer commonly is called artesian pressure, and the formation containing artesian water is an artesian aquifer or confined aquifer.
See also flowing well

Artesian Wells
Wells (bore holes) that penetrate artesian aquifers. Water will rise up the well casing to the pressure level of the aquifer. Artesian flow describes the natural flow to the surface of water from confined aquifers. In some parts of the US any well drilled into bedrock is (incorrectly) called an artesian well.

Artificial Recharge
A process where water is put back into ground water storage by use of engineering devices such as spreading basins or recharge wells. See also ASR

ASR (Aquifer Storage Recovery)
A management strategy involving engineered devices such as detention ponds or recharge wells that deliberately adds water to ground water storage with a view to later withdrawal for some economic purpose. ASR is likely to become an increasingly important water management strategy in the western USA.