Rain water and precipitation flow into permeable layers of the Floridan aquifer to become groundwater. Once in the ground, some of this water travels close to the land surface and emerges very quickly as discharge into streambeds. However, due to gravity, much of it continues to sink deeper into the ground. When this water falls below the water table, which is the underground depth at which point the ground is totally saturated by water, it can move both vertically and horizontally.
The Floridan aquifer system has been defined on the basis of permeability. The Upper Floridan is highly permeable in most places and yields sufficient water supplies for most purposes, so there is generally less need to drill into the deeper Lower Floridan aquifer. The confining unit separating the Upper and Lower Floridan aquifers is present at different altitudes and consists of different rocks from place to place. Wherever the middle confining unit is present, it restricts the movement of ground water between the Upper and Lower Floridan aquifers.
The geologic characteristics and hydraulic properties of the Lower Floridan aquifer have not been studied as extensively as the Upper Floridan aquifer due to its greater depths. Much of the Lower Floridan aquifer contains saltwater. Two important and highly permeable zones are present within the Lower Floridan aquifer. One of these zones is the source of a considerable volume of fresh to brackish water that moves upward through the middle confining unit and ultimately reaches the Upper Floridan aquifer. The second zone is an extremely permeable cavernous zone in Southeastern Florida. This zone contains saltwater and is used as the receiving zone for treated sewage and other wastes disposed through injection wells. This zone is overlain in most places by a confining unit that prevents upward movement of the injected waste. The cavernous nature of these two zones was created by vigorous circulation of ground water through the carbonate rocks in the geologic past, and does not results from the present ground-water flow system.
The Floridan aquifer system has been defined on the basis of permeability. The Upper Floridan is highly permeable in most places and yields sufficient water supplies for most purposes, so there is generally less need to drill into the deeper Lower Floridan aquifer. The confining unit separating the Upper and Lower Floridan aquifers is present at different altitudes and consists of different rocks from place to place. Wherever the middle confining unit is present, it restricts the movement of ground water between the Upper and Lower Floridan aquifers.
The geologic characteristics and hydraulic properties of the Lower Floridan aquifer have not been studied as extensively as the Upper Floridan aquifer due to its greater depths. Much of the Lower Floridan aquifer contains saltwater. Two important and highly permeable zones are present within the Lower Floridan aquifer. One of these zones is the source of a considerable volume of fresh to brackish water that moves upward through the middle confining unit and ultimately reaches the Upper Floridan aquifer. The second zone is an extremely permeable cavernous zone in Southeastern Florida. This zone contains saltwater and is used as the receiving zone for treated sewage and other wastes disposed through injection wells. This zone is overlain in most places by a confining unit that prevents upward movement of the injected waste. The cavernous nature of these two zones was created by vigorous circulation of ground water through the carbonate rocks in the geologic past, and does not results from the present ground-water flow system.
Sinkholes are a common feature of the Floridan aquifer system. Sinkholes are found in places underlain by soluble rocks such as the limestone and dolomite that form the aquifer system. They usually form by gradual subsidence of the land surface in response to dissolution of limestone. Sinkholes naturally form slowly and expand gradually, however, some sinkholes can form abruptly, which are known as collapse sinkholes.