An aquifer is a geological formation of permeable rock, sand or gravel that stores and transmits groundwater in quantities sufficient for extraction through wells or springs.
Aquifers are essential components of the water cycle and serve as the primary source of drinking water, agricultural irrigation and industrial water supply in many regions around the world.
Types of aquifers
- Unconfined aquifer — the upper surface of the water (the water table) is open to atmospheric pressure. Rainwater percolates directly downward through the soil to recharge the aquifer. These aquifers are more vulnerable to contamination from surface activities.
- Confined aquifer — sandwiched between two impermeable layers (aquitards or aquicludes), such as clay or dense rock. Water in a confined aquifer is under pressure; when a well penetrates the confining layer, water rises in the borehole (and may even flow at the surface as an artesian well).
- Semi-confined aquifer — bounded by layers that are not fully impermeable, allowing some slow leakage of water between layers.
Key properties
- Porosity — the percentage of the rock or sediment volume that consists of open pore spaces. Higher porosity means more water can be stored.
- Permeability (hydraulic conductivity) — the ease with which water can flow through the material. Sand and gravel have high permeability; clay has very low permeability.
- Transmissivity — the rate at which water is transmitted through the full thickness of the aquifer.
- Storage coefficient — the volume of water released or absorbed per unit area per unit change in hydraulic head.
Relevance to construction
Builders and engineers must understand aquifer conditions because:
- High groundwater levels affect foundation design, requiring waterproofing, drainage or even permanent dewatering.
- Excavations below the water table need dewatering systems that may lower the water table and impact nearby structures or ecosystems.
- Contamination of aquifers during construction (fuel spills, cement washout) can have serious environmental consequences.
Related terms
- Groundwater table
- Dewatering
- Artesian well
- Aquitard