Aquifers are replenished by infiltrating rainfall or surface streams that can penetrate overlying soils. Any changes that occur in the elevation of the water table reflect a net recharge to or discharge from the aquifer. The aquifers in Tennessee are composed of several different rock types. Typical Features of Carbonate Rock Land forms that develop in carbonate terrain are referred to as karst , and are characterized by gently rolling hills, with depressions and sinkholes. Some sinkholes are created by collapse of overlying soils into underground cavities in the carbonate rock.
Sinkholes also form by the weathering and dissolving of surface carbonate rocks.
As the rock dissolves, small fractures and cracks become larger and may connect to form an extensive subterranean drainage system. Under certain conditions caves may form, and if the water table falls, surface streams may disappear into the underground tunnels. In karst terrain it is not unusual for a disappearing surface stream to reemerge elsewhere as a natural spring. In the event that a potential migrating contaminant can enter a stream, it is highly likely that the same contaminant may resurface at a spring. Carbonate rock exhibiting fractures and caves.