Aquifer Characteristics
Groundwater is stored in the open spaces and fractures within geologic materials such as soil, sand, and rock that occur beneath the land surface. Aquifers are the geologic layers that are filled with water and that can transmit enough water to supply a well under normal
hydraulic gradients
.
Aquifer Types
Geologic materials can be classified as consolidated rock or unconsolidated (loose) sediment. Consolidated rock may consist of such materials as sandstone,
shale, granite, and basalt. Unconsolidated sediment contains granular material such as sand, gravel, silt, and clay. The four major types of aquifers are: