Glossary Groundwater
  • A

  • AbsorptionThe process by which substances in gaseous liquid or solid form dissolve or mix with other substances
  • Adsorption

    Adherence of gas molecules ions or molecules in solution to the surface of solids

  • Adsorption isotherm

    A graphical representation of the relationship between the bulk activity of adsorbate and the amount adsorbed at constant temperature

  • Advection

    The process whereby solutes are transported by the bulk mass of flowing fluid

  • Aeration zone

    The zone immediately below the land surface where the pores contain both water and air but are not totally saturated with water. Plant roots can capture the moisture passing through this zone but it cannot provide water for wells. Also known as the unsaturated zone or vadose zone.

  • Air-space-ratio

    The ratio of (a) the volume of water that can be drained from a saturated soil or rock under the action of force of gravity to (b) the total volume of voids

  • Anisotropic mass

    A mass having different properties in different directions at any given point

  • Anisotropy

    The condition of having different properties in different directions

  • Apparent groundwater velocity

    See specific discharge

  • Aquiclude

    A hydrogeologic unit which although porous and capable of storing water does not transmit it at rates sufficient to furnish an appreciable supply for a well or spring

  • Aquifer

    (1) A formation group of formations or part of a formation that contains sufficient saturated permeable material to yield significant quantities of water to wells and springs (2) A geologic formation group of formations or part of a formation capable of yielding a significant amount of groundwater to wells or springs. Any saturated zone created by uranium or thorium recovery operations would not be considered an aquifer unless the zone is

  • Aquifer storage and retrieval (ASR)

    Use of a well or series of wells to inject surface water into an aquifer during wet weather or low demand periods for purposes of withdrawal and use during drought and/or high demand periods.

  • Aquifer system

    A body of permeable and poorly permeable material that functions regionally as a water-yielding unit; it comprises two or more permeable beds separated at least locally by confining beds that impede groundwater movement but do not greatly affect the regional hydraulic continuity of the system; includes both saturated and unsaturated parts of permeable material

  • Aquifer test

    A test to determine hydrologic properties of the aquifer involving the withdrawal of measured quantities of water from or addition of water to a well and the measurement of resulting changes in head in the aquifer both during and after the period of discharge or additions

  • Aquifuge

    (1) A hydrogeologic unit which has no interconnected openings and hence cannot store or transmit water (2) A rock which contains no interconnected openings or interstices and therefore neither stores nor transmits water (3) An impermeable rock

  • Aquitard

    A confining bed that retards but does not prevent the flow of water to or from an adjacent aquifer; a leaky confining bed. It does not readily yield water to wells or springs but may serve as a storage unit for ground water

  • Area of influence of a well

    The area surrounding a pumping or recharging well within which the potentiometric surface has been changed

  • Artesian

    Synonymous with confined

  • Artesian aquifer

    Synonymous with confined aquifer

  • Artesian well

    A well tapping a confined aquifer. Water in the well rises above the top of the aquifer under artesian pressure but does not necessarily reach the land surface; a flowing artesian well is a well in which the water level is above the land surface.

  • Artificial recharge

    Putting water back into groundwater storage from surface water supplies such as irrigation or induced infiltration from streams or wells. Includes aquifer storage and retrieval (ASR).

  • Average interstitial velocity

    See velocity average interstitial

  • B

  • Baseflow

    Streamflow coming from groundwater seepage into a stream or river. Groundwater flows underground until the water table intersects the land surface and the flowing water becomes surface water in the form of springs streams/rivers lakes and wetlands. Baseflow is the continual contribution of groundwater to rivers and is an important source of flow between rainstorms.

  • Baseline monitoring

    The establishment and operation of a designed surveillance system for continuous or periodic measurements and recording of existing and changing conditions that will be compared with future observations

  • Best management practices (BMP

    Structural nonstructural and managerial techniques recognized to be the most effective and practical means to reduce surface water and groundwater contamination while still allowing the productive use of resources.

  • Brackish

    Mixed fresh and salt water.

  • Breakthrough curve

    A plot of relative concentration versus time where relative concentration is defined as C/Co with C as the concentration at a point in the groundwater flow domain and Co as the source concentration.

  • Buildup

    The vertical distance the water table or potentiometric surface is raised or the increase of the pressure head due to the addition of water.

  • C

  • Capillary action

    The movement of water in the interstices of a porous medium due to capillary forces. Synonymous with capillarity capillary flow and capillary migration.

  • Capillary conductivity

    (1) The property of an unsaturated porous medium to transmit liquid (2) Coefficient which expresses the extent to which an unsaturated permeable medium allows flow of water through its interstices under a unit gradient of capillary potential