Aquifers & Springs

Aquifers are underground rocks that hold water. In Florida, three aquifers are used for water supply: the Floridian aquifer, the intermediate aquifer and the surficial aquifer. In some parts of the state the intermediate aquifer is between the surficial aquifer and the Floridian aquifer. In northwest Florida, the surficial aquifer is called the sand and gravel aquifer, and in southeast Florida it is called the Biscayne aquifer.

The Floridian aquifer has been called Florida’s rain barrel (Parker 1951) and is one of the most productive aquifers in the world. Each day Floridians use about 2.5 billion gallons of water from the Floridian aquifer. It underlies 250,000 square kilometers (100,000 square miles) in southern Alabama, southeastern Georgia, southern South Carolina and all of Florida. Over most of Florida, the Floridian aquifer is covered by sand, clayA fine-grained, firm earthy material that is plastic when wet and hardens when heated, consisting primarily of hydrated silicates of aluminum and widely used in making bricks, tiles, and pottery; used for liners in landfills because it is impervious. or limestoneSedimentary rock composed of carbonate minerals, especially calcium carbonate. Limestone can be created by clastic and non-clastic processes. Clastic limestones are formed from the break up and deposition of shells, coral and other marine organisms by wave-action and ocean currents. Non-clastic limestones can be formed either as a precipitate or by the lithification of coral reefs, marine organism shells, or marine organism skeletons. that ranges in thickness from a few feet in parts of west-central and north-central Florida to hundreds of feet in southeastern Georgia, northeastern Florida, southeastern Florida and the westernmost Panhandle.

Within the aquifer, water may travel quickly or very slowly. In parts of the aquifer with caves and large conduits, water may travel several miles in only a few hours. Where water-filled spaces are small and underground routes convoluted, it may take days, weeks or even years for water to travel the same distance. In the past several decades, increased pumping of ground water has lowered water levels in the Floridian aquifer in several places in Florida and Georgia, including the Panhandle, northeastern and southwestern Florida, and southeastern and coastal Georgia (Berndt et al. 1998).

Water is replaced in the Floridian aquifer by rainfall that soaks into the ground. This is referred to as recharge. Recharge does not occur everywhere. In some places (mostly along the coasts and south of Lake Okeechobee) water flows out of, rather than into, the aquifer. This is referred to as discharge. In other areas, thick clay covers the aquifer and slows or stops the downward flow of water. Areas of high recharge only occur in about 15 percent of the state and include the well drained sand ridges of central and west central Florida. Sand is porous, which means water can easily flow through it.

Limiting intensive development in high recharge areasThe area on the Earth's surface that receives water for storage into a particular aquifer. is critical for maintaining water supplies: water cannot soak through pavement.

In some parts of Florida, the Floridian aquifer is not a suitable or drinkable source of fresh waterWater that is relatively free of salts.. In some places, it is too far below the surface; in other places, the water is salty. The surficial sand and gravel aquifer is the major source of fresh water in Escambia and Okaloosa counties in northwest Florida, and the surficial Biscayne aquifer is the major source of fresh water in Dade and Broward counties in southeast Florida. This aquifer is an important source of fresh waterWater that is relatively free of salts. in Sarasota, Charlotte and Glades counties. The remainder of the state uses the Floridian aquifer as its main source of drinking water.

The pages below with respect to Citrus County and Levy County depict a detailed analysis conducted for the THE CITRUS COUNTY AQUIFER VULNERABILITY ASSESSMENT - Part of Phase II of the Florida Aquifer Vulnerability Assessment (FAVA) Project, Florida Department of Environmental Protection Contract No. RM059, completed in July , 2008.

Ground water flows are not considered in the FAV/CAVA/LCAVA studies. Essentially there are two primary influences which contribute to underground direction and rate of flow.

PiezometricA measure of pressure of water, especially in an aquifer. Shows altitude at which water would have stood in a tightly cased well relative to a given sea level. See also potentiometric surface. flows occur from higher levels to lower levels of the potentiometric surfacean imaginary surface defined by the level to which water in an aquifer would rise in a well due to the natural pressure in the rocks., in a direction normal (at right angle) to lines joining points of equal pressure (also termed contours). Rates of flow depend upon the permeability of the type of rock formation encountered in the path of flow. In geology, when a tilted formation receives water (from rainfall or otherwise), water enters the formation and flows downward. If the bottom of this formation is exposed to the air, this water will flow up and out of the formation in an artesian well, or a spring vent, because of the force of the water behind it that is also flowing downhill.

When piezometricA measure of pressure of water, especially in an aquifer. Shows altitude at which water would have stood in a tightly cased well relative to a given sea level. See also potentiometric surface. flows encounter fracture sets in a formation the flow direction changes to follow the path of least resistance, and faster flow rate, to follow the direction of the fracture set. This may be observed in the direction taken in a river fed from spring vents occurring along fracture sets as seen in Kings Bay in the direction to Bagley Cove, a direction from southeast to northwest. A fracture set can be clearly seen linking Black Spring with a spring to the southeast in Kings Creek.

For a discussion on how geology of a region effects ground water flows click here.