Groundwater Definitions
Aquifer: An underground geological formation able to store and yield water (see artesian, confined, and unconfined aquifers).
Artesian (or confined) aquifer: 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.
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.
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.
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.
Decommissioning a well: The process of sealing a well that is no longer being used to prevent groundwater contamination and harm to people and animals.
Drawdown: A lowering of the groundwater level caused by pumping.
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.
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.
Karst: A geologic formation of irregular limestone deposits that dissolve to form sink holes, underground streams, and caverns.
Groundwater Mining: Withdrawal (removal) of groundwater over a period of time that exceeds the recharge rate of the supply aquifer. Also referred to as overdraft or mining the aquifer.
Monitoring well: A non-pumping well, generally of small diameter, that is used to measure the elevation of a water table or water quality. A piezometer, which is open only at the top and bottom of its casing, is one type of monitoring well.
Perched aquifer: Localized zone of saturation above the main water table created by an underlying layer of impermeable material.
Permeable/Permeability: Capable of transmitting water (porous rock, sediment, or soil); the rate at which water moves through rocks or soil.
Permeable layer: A layer of porous material (rock, soil, unconsolidated sediment); in an aquifer, the layer through which water freely passes as it moves through the ground.
Pore space: Openings between geologic material found underground. Also referred to as void space or interstices.
Porosity: The ratio of the volume of void or air spaces in a rock or sediment to the total volume of the rock or sediment. The capacity of rock or soil to hold water varies with the material. For example, saturated small grain sand contains less water than coarse gravel.
Potentiometric surface: The potential level to which water will rise above the water level in an aquifer in a well that penetrates a confined aquifer; if the potential level is higher than the land surface, the well will overflow. See artesian well and confined aquifer.
Recharge: Water added to an aquifer. For example, when rainwater seeps into the ground. Recharge may occur artificially through injection wells or by spreading water over groundwater reservoirs.
Recharge rate: The quantity of water per unit of time that replenishes or refills an aquifer.
Saturated thickness: Total water-bearing thickness of an aquifer.
Spring: The emergence of groundwater at the land surface, usually at a clearly defined point; it may flow strongly or just ooze or seep out.
Transmissivity: A measure of the capability of the entire thickness of an aquifer to transmit water. Also known as coefficient of transmissivity.
Unconfined aquifers: An aquifer in which the water table is at or near atmosphere pressure and is the upper boundary of the aquifer. Because the aquifer is not under pressure the water level in a well is the same as the water table outside the well.
Unsaturated 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.
Watershed: The land area from which surface runoff drains into a stream, channel, lake, reservoir, or other body of water; also called a drainage basin.
Wellhead Protection Area
Water table: The top of an unconfined aquifer; indicates the level below which soil and rock are saturated with water.
Well: A bored, drilled or driven shaft, or a dug hole whose depth is greater than the largest surface dimension and whose purpose is to reach underground water supplies to inject, extract or monitor water.
Wellhead protection area: A protected surface and subsurface zone surrounding a well or well field supplying a public water system to keep contaminants from reaching the well water.
Wetlands: Lands where water saturation is the dominant factor in determining the nature of soil development and the types of plant and animal communities. Other common names for wetlands are sloughs, ponds, and marshes.
All definitions from The Groundwater Foundation.
