Adhesion

The attraction of water molecules to solid surfaces.

Aquifer

An underground unit of saturated soil or rock that can transmit significant quantities of water to wells.

Artesian aquifer

See confined aquifer.

Baseflow

The component of flow in streams that comes from groundwater discharge.

Capillarity

The phenomenon by which water rises in small pores into the unsaturated zone above the water table, because of adhesive and cohesive forces.

Cohesion

The attraction of water molecules to each other because of hydrogen bonding.  Also known as surface tension.

Cone of depression

The zone around a well in an unconfined aquifer that is normally saturated, but becomes unsaturated when the well is pumped.

Confined aquifer

An aquifer that is bounded above and below by confining layers which transmit water significantly slower than the aquifer.  The water level in a well, tapping a confined aquifer, will rise above the top of the aquifer because the confined aquifer is under pressure.  Also called artesian aquifer.

Confining

layer

A layer of lower permeability material that overlies an aquifer.  Sometimes called an aquitard.

Dilution

A greater volume of groundwater being mixed with the same amount of contaminant.

Discharge

The removal of groundwater from an aquifer at lakes, streams or wetlands, by pumping a well, or by leakage to another aquifer.

Dispersion

Water carrying a contaminant becoming more separated by following a variety of distinct flow paths through an aquifer.  Dispersion has two components: mechanical mixing and diffusion.

Drawdown

A lowering of the water table in an unconfined aquifer or the potentiometric surface in a confined aquifer caused by pumping of a well.

Elevation

head

The difference in elevation between the recharge area and the discharge area.

Evaporation

The process by which water is changed from a liquid or solid to a vapor at a temperature below the boiling point.

Evapotrans- piration

Water returned to the atmosphere by evaporation from land and water, and by transpiration of living plants.

Groundwater

Water contained in saturated soil and rock materials below the surface of the ground.

Heat of

Fusion

The energy given off as water changes forms from a liquid to a solid.

Heat of vaporization

The energy consumed as water changes forms from a liquid to a gas.

Heat of conductivity

The rate of flow of groundwater in gallons-per-day conductivity through a cross-section of one square foot under a unit hydraulic gradient at the prevailing temperature.  Hydraulic conductivity is related both to the type of earth materials and the water present in an aquifer.

Hydraulic

head

The energy that causes groundwater to flow.  It is the sum of the gravitational energy and the pressure energy.

Hydrogen bonding

The cohesive force caused by the polar nature of water, in which the oxygen atom in one water molecule is attracted to the hydrogen atom of another water molecule.  This bonding causes water to have many of its unique properties.

Hydrologic cycle

The circulation of water from the land and bodies of water to the atmosphere and back again.

Indicator

A chemical or biological parameter that can be used to indicate the possible presence of other contaminants.

Permeability

The capacity of rock or unconsolidated material to transmit a liquid, which is primarily a function of the sizes of the interconnected pores and the shapes of the openings.

Piezometer

A well installed to monitor hydraulic head or to monitor groundwater quality.

Porosity

The ratio of the volume of void spaces in a rock or sediment to the total volume of the rock or sediment.

Potentiometric

The level to which water rises in a well drilled into a confined aquifer surface.

Pressure

The energy given to groundwater by the weight of energy overlying water and earth materials.

Recharge

The addition of water to the groundwater through the infiltration of precipitation through the unsaturated zone into the aquifer.

Saturated zone

The part of a water-bearing formation in which all the void spaces are filled with water.

Specific

heat

The number of calories required to raise the temperature of water one degree.

Spring

A natural discharge of groundwater at the land surface.

Texture

The percentage of silt, sand, and clay materials making up a soil.

Unconfined aquifer

An aquifer which has no confining layers above it, so that the water table is exposed to atmospheric pressure and forms the upper boundary of the aquifer.

Unsaturated zone

The zone between the land surface and the water table, in which some of the pore spaces are filled with air and some are filled with water.

Water table

The level below which the soil or rock is saturated with water.  The upper surface of the saturated zone in an unconfined aquifer.