GEOLOGY

Detailed explanation-1: -In the subsurface, rocks serve either as confining units or aquifers. A confining unit or aquitard is characterized by low permeability that does not readily permit water to pass through it. Confining units do, however, store large quantities of water. Examples include shale, clay, and silt.

Detailed explanation-2: -Clay is the most porous sediment but is the least permeable. Clay usually acts as an aquitard, impeding the flow of water.

Detailed explanation-3: -For groundwater to be able to get into a rock with good porosity it must also have good permeability. For a rock to be permeable and for water to move through it, the pore spaces between the grains in the rock must be connected. Permeability is therefore a measure of the ability of water to move through a rock.

Detailed explanation-4: -Because they have large and connected spaces, materials such as sand and gravel allow water to pass through, or permeate. They are thus known as permeable materials. As water soaks down through permeable rock and soil, it eventually reaches layers of material that it cannot pass through.

Detailed explanation-5: -Permeability is a measure of the interconnectedness of pores. The connection between pore spaces allows groundwater to flow through the sediment or rock. The combination of water storage (porosity) and flow (permeability) makes a good aquifer-a rock unit or sediment that contains usable groundwater.