The most basic groundwater Glossary: Part 1: A-I

A
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.
Aquiclude: Impermeable beds of geologic material that hinder or prevent groundwater movement.
Aquifer: An underground geological formation able to store and yield water.
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.
Artesian aquifer: See 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).
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.
Best management practices (BMP’s): 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.
C
Capillary water: Just above the water table, in the aeration zone, is capillary water that moves upward from the water table by capillary action. This water can move slowly and in any direction. While most plants rely upon moisture from precipitation that is present in the unsaturated zone, their roots may also tap into capillary water or into the underlying saturated zone.

Collection site: A stream, lake, reservoir, or other body of water fed by water drained from a watershed.

Condensation: The process in the hydrologic cycle by which a vapor becomes a liquid; the opposite of evaporation.
Cone of depression: The zone around a well in an unconfined aquifer that is normally saturated, but becomes unsaturated as a well is pumped, leaving an area where the water table dips down to form a cone shape. The shape of the cone is influenced by porosity and the water yield or pumping rate of the well. The land surface overlying the cone of depression is referred to as the area of influence.
Confined aquifer: (also known as artesian or pressure aquifers) exist where the groundwater is bounded between layers of impermeable substances like clay or dense rock. When tapped by a well, water in confined aquifers is forced up, sometimes above the soil surface. This is how a flowing artesian well is formed.
Confining layer: Geologic material with little or no permeability or hydraulic conductivity. Water does not pass through this layer or the rate of movement is extremely slow.
Conservation: The use of water-saving methods to reduce the amount of water needed for homes, lawns, farming, and industry, and thus increasing water supplies for optimum long-term economic and social benefits.
Consolidated rock: Tightly bound geologic formation composed of sandstone, limestone, granite, or other rock.
Consumptive use: The use of a resource that reduces the supply (removing water from a source like a river, lake or aquifer without returning an equal amount). Examples include the intake of water by plants, humans, and other animals and the incorporation of water into the products of industrial or food processing.
Contaminant: Any substance that when added to water (or another substance) makes it impure and unfit for consumption or an intended use.
D
Darcy’s Law: A groundwater movement equation formulated by Henry Darcy during the mid-1800's based on experiments on the flow of water through beds of sand. Darcy's Law forms the scientific basis of fluid permeability used in earth science.
Depletion: The loss of water from surface water reservoirs or groundwater aquifers at a rate greater than that of recharge.

Diffusion: The movement of a substance from an area of high concentration to an area of low concentration.

Discharge: An outflow of water from a stream, pipe, groundwater aquifer, or watershed; the opposite of recharge.
Discharge area: The area or zone where groundwater emerges from the aquifer. The outflow maybe into a stream, lake, spring, wetland, etc.
Drawdown: A lowering of the groundwater level caused by pumping.
Drought: An extended period with little or no precipitation; often affects crop production and availability of water supplies.
E
Erosion: The wearing down or washing away of the soil and land surface by the action of water, wind, or ice.

Evaporation: The conversion of a liquid (water) into a vapor (a gaseous state) usually through the application of heat energy during the hydrologic cycle; the opposite of condensation.

Evapotranspiration: The loss water from the soil through both evaporation and transpiration from plants.
F
Filtering: The soil's ability to attenuate substances by retaining chemicals or dissolved substances on the soil particle surface, transforming chemicals through microbial biological processing, retarding movement, and capturing solid particles.
Flow rate: The time required for a volume of groundwater to move between points. Typically groundwater moves very slowly—sometimes as little as inches per year.
Fresh water: Water with less than 0.5 parts per thousand dissolved salts.
G
Gaining stream: A stream in which groundwater discharges contribute significantly to the streamflow volume. The same stream could be both a gaining stream and a losing stream, depending on the conditions.
Gas (gaseous): See vapor.
Gray water: Domestic wastewater composed of wash water from household sinks, tubs, and washers.
Groundwater: Water found in the spaces between soil particles and cracks in rocks underground (located in the saturation zone). Groundwater is a natural resource that is used for drinking, recreation, industry, and growing crops.
Groundwater basin: The underground area from which groundwater drains. The basins could be separated by geologic or hydrologic boundaries.
Groundwater divide: The boundary between two adjacent groundwater basins, which is represented by a high point in the water table.
Groundwater under the direct influence (UDI) of surface water: A groundwater source located close enough to nearby surface water, such as a river or lake, to receive direct surface water recharge. Since a portion of the groundwater source’s recharge is from surface water, the groundwater is at risk of contamination from pathogens such as Giardia lamblia and viruses, which are not normally found in groundwater.
H
Hydrogeology: The study of the interrelationships of geologic materials and processes with water, especially groundwater.
Hydrologic cycle: (also known as the water cycle) The paths water takes through its various states--vapor, liquid, solid--as it moves throughout the oceans, atmosphere, groundwater, streams, etc.
Hydrology: The study of the occurrence, distribution, and chemistry of all waters of the earth.
I
Impermeable layer: A layer of material (such as clay) in an aquifer through which water does not pass.
Induced recharge: The recharge to an aquifer that occurs when a pumping well creates a cone of depression that lowers an adjacent water table below the level of a stream or lake, causing the stream or lake to lose water to the adjacent groundwater aquifer.
Infiltration: Flow of water from the land surface into the subsurface.
Infiltration rate: The quantity of water that enters the soil surface in a specified time interval. Often expressed in volume of water per unit of soil surface area per unit of time.
Injection well: A well constructed for the purpose of injecting treated water, often wastewater, directly into the ground. Water is generally forced (pumped) into the well for dispersal or storage into a designated aquifer. Injection wells are generally drilled into aquifers that are not used as a drinking water source, unused aquifers, or below freshwater levels.
Integrated management: Any combination of physical, technical, administrative, and legal practices relating to surface water and groundwater in a manner designed to increase combined benefits or achieve a more equitable apportionment of benefits from both sources. Also referred to as conjunctive use.
Interflow: Water that travels laterally or horizontally through the aeration zone during or immediately after a precipitation event and discharges into a stream or other body of water.
Irrigation: The controlled application of water to cropland, hay fields, and/or pasture to supplement that supplied by nature.

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