Where is groundwater stored?
Groundwater is stored below the surface of the earth within a structure called an aquifer. An aquifer is made out of permeable or porous rock material and is saturated (soaked) with groundwater. Graphic from USGS http://water.usgs.gov/ogw/ The characteristics of particular rock types determine the type of aquifer present. Unconsolidated aquifers are composed of sand and/or gravel. These types of aquifers vary in permeability. Sand and gravel are very permeable and make the best aquifers. Clay and shale are very impermeable, and do not make a good aquifers. Consolidated aquifers are composed of fractured rock material. The rocks present in these aquifers are usually granites, basalts, and limestone. Water flows through the cracks in the rocks and can be drawn out for use (USGS). Aquifers can also be defined as confined and unconfined. Confined aquifers are rarer than unconfined aquifers, and occur when the saturated zone lies between two layers of impermeable rock. These types of aquife
