CHAPTER 9: GROUNDWATER

The portion of the Earth’s freshwater stored beneath the surface in soil and rock layers.

Groundwater

The zone where all pores are filled with water, forming a continuous body of groundwater.

Saturated Zone

The zone containing both air and water within the soil pores.

Zone of Aeration (Vadose Zone)

The upper surface of the saturated zone, marking the boundary between saturated and unsaturated soil.

Water Table

A localized impervious layer trapping water above the main water table.

Perched Water Table

A geological formation that stores and transmits groundwater in sufficient quantity.

Aquifer

A formation that stores water but does not allow significant movement of groundwater.

Aquiclude

A formation that transmits water slowly compared to an aquifer.

Aquitard

A formation that neither stores nor transmits water.

Aquifuge

A groundwater reservoir open to the atmosphere and recharged directly by rainfall.

Unconfined Aquifer

A water-bearing layer trapped between impermeable strata, with water under pressure.

Confined (Artesian) Aquifer

The ratio of void volume to total volume in a rock or soil sample.

Porosity

The volume of water that drains freely by gravity from a saturated material.

Specific Yield

The portion of water retained by adhesion and surface tension that cannot drain.

Specific Retention

The ability of an aquifer to transmit groundwater, equal to hydraulic conductivity times thickness.

Transmissibility

The volume of water released per unit volume per unit decline in hydraulic head.

Specific Storage (Ss)

The parameter expressing an aquifer’s ability to release or store water per unit area.

Storage Coefficient (S)

The hydraulic structure used to extract groundwater by drilling or excavation.

Well

The cone-shaped lowering of the water table around a pumping well.

Cone of Depression

The vertical lowering of water level in a well due to pumping.

Drawdown

The distance from the well to the outer limit of the drawdown influence.

Radius of Influence

The recovery of water level after pumping stops.

Recuperation

The discharge per unit drawdown used to measure well performance.

Specific Capacity

The addition of surface water to the saturated zone, either naturally or artificially.

Recharge

The maximum rate of withdrawal without producing long-term depletion of the aquifer.

Safe Yield