Water Resources Center

Groundwater Terms and Definitions

air line - consists of a small-diameter plastic pipe or tube of sufficient length to extend from the top fo the well to a point several feet below the lowest anticipated water level to be reached during a pump test

alluvium - a general term for clay, silt, sand, gravel, or similar unconsolidated material deposited during comparatively recent geologic time by a stream or other body of running water as a sorted or semisorted sediment in the bed of the stream or on its floodplain or delta, or as a cone or fan at the base of a mountain slope

anisotropic - having some physical property that varies with direction

aquifer - a formation, group of formations, or part of a formation that contains sufficient saturated permeable material to yield economical quantities of water to wells and springs

boundary condition -

confined aquifer - a formation in which the groundwater is isolated from the atmosphere at the point of discharge by impermeable geologic formations; confined groundwater is generally subject to pressure greater than atmospheric

consolidated -

Darcy’s Law - a derived equation for the flow of fluids on the assumption that the flow is laminar and that inertia can be neglected Q= (-)K * i * A

dolomite - a sedimentary rock consisting chiefly of calcium, magnesium carbonate

drawdown - the distance between the static water level and the surface of the cone of depression

geologic formation - the geological features of the earth

glacial drift - a general term for unconsolidated sediment transported by glaciers and deposited directly on land or in the sea

glacial till - unsorted mixture of materials and rock fragments deposited directly by a glacier. Generally have high clay content and low permeability.

heterogeneous - nonuniform in structure or composition throughout

homogeneous - uniform in structure or composition throughout

hydraulic conductivity - the rate of flow of water in gallons per day through a cross section of one square foot under a unit hydraulic gradient, at the prevailing temperature

isotropic - said of a medium whose properties are the same in all directions

karst - a type of topography that is formed on limestone, gypsum, and other rocks by dissolution, and is characterized by sinkholes, caves, and underground drainage

limestone - a sedimentary rock consisting chiefly of calcium carbonate

permeability - the property or capacity of a porous rock, sediment, or soil for transmitting a fluid; it is a measure of the relative ease of fluid flow under unequal pressure

phreatic - water that enters freely into wells under both confined and unconfined conditions

porosity - the percentage of the bulk volume of a rock or soil that is occupied by interstices, whether isolated or connected

preglacial channel -

pumping level - the level at which water stands in a well when pumping is in progress

safe yield -

saturated thickness - a thickness of soil or rock that the voids contained within are 100 percent saturated with water or other fluid

specific retention - the ratio of the volume of water that a given body of rock or soil will hold against the pull of gravity to the volume of the body itself, expressed as a percentage

specific yield - the ratio of the volume of water that a given mass of saturated rock or soil will yield by gravity to the volume of that mass, stated as a percentage

static water level - the level of water in a well that is not being affected by withdrawal of groundwater

storage coefficient - the volume of water an aquifer releases from or takes into storage per unit surface area of the aquifer per unit change in head

transmissivity - the rate at which water is transmitted through a unit width of an aquifer under a unit hydraulic gradient

unconfined aquifer - an aquifer where the water table is exposed to the atmosphere through openings in the overlying materials

unconsolidated -

vadose - the zone containing water under pressure less than that of the atmosphere, including soil water, intermediate vadose water, and capillary water

well interference - the condition occurring when the area of influence of a water well comes into contact with/or overlaps that of a neighboring well, as when two wells are pumping from the same aquifer or located near each other