The Floridan aquifer system, composed of the Upper and Lower Floridan aquifers, is a sequence of Paleogene carbonate rock which spans an area of about in the southeastern United States. It underlies the entire state of Florida and parts of Alabama, Georgia, Mississippi, and South Carolina.
The Floridan aquifer system is one of the world's most productive aquifers and supplies drinking water for nearly 10 million people.Marella, R.L., and Berndt, M.P., 2005, Water withdrawals and trends from the Floridan aquifer system in the southeastern United States, 1950-2000: U.S. Geological Survey Circular 1278, 20 p., https://pubs.er.usgs.gov/publication/cir1278. According to the United States Geological Survey, total withdrawals from the Floridan aquifer system in 2000 were ranked 5th highest of all principal aquifers in the nation at 3,640 million gallons per day (Mgal/d) ().Maupin, M.A., and Barber, N.L., 2005, Estimated withdrawals from principal aquifers in the United States, 2000: U.S. Geological Survey Circular 1279, 46 p., https://pubs.er.usgs.gov/publication/cir1279 Usage was broken down as 49% (1,949 Mgal/d; ) for irrigation, 33% (1,329 Mgal/d; ) for public water supply, 14% (576 Mgal/d, ) for industrial purposes, and 4% for domestic self-supplied withdrawals. The system is the primary source of drinking water for most cities in central and northern Florida as well as eastern and southern Georgia.
History
In 1936, geologist Victor Timothy (V.T.) Stringfield first identified the existence of the Floridan Aquifer in peninsular Florida and referred to the carbonate units as the "principal artesian formations."Stringfield, V.T., 1936, Artesian water in the Florida peninsula: Water Supply Paper 773-C, https://pubs.er.usgs.gov/publication/wsp773C In 1944, M.A. Warren of the Georgia Geological Survey described an extension of this system in southern Georgia and applied the term "principal artesian aquifer" to the carbonate rock involved.Warren, M.A., 1944, Artesian water in southeastern Georgia, with special reference to the coastal area: Georgia Geological Survey Bulletin 49, 140 p., https://epd.georgia.gov/sites/epd.georgia.gov/files/related_files/site_page/B-49.pdf In 1953 and 1966 Stringfield also applied the term "principal artesian aquifer" to these rocks.Stringfield, V.T., 1953, Artesian water in the Southeastern States, in McCrain, Preston, eds, Proceedings of the southeastern mineral symposium 1950: Kentucky Geological Survey Series 9, Special Publication 1, p. 24-39.Stringfield, V.T., and LeGrand, H.E., 1966, Hydrology of Limestone Terranes in the Coastal Plain of the Southeastern United States: Geological Society of America Special Papers, v. 93, p. 1–46. In 1955, Garald G. Parker noted the hydrologic and lithologic similarities of the Tertiary carbonate formations in southeast Florida, concluded that they represented a single hydrologic unit, and named that unit the "Floridan aquifer".Parker, G.G., Ferguson, G.E., and Love, S.K., 1955, Water resources of southeastern Florida, with special reference to geology and ground water of the Miami area: U.S. G.P.O., Water Supply Paper 1255, https://pubs.er.usgs.gov/publication/wsp1255. With additional information collection, more zones of high and low hydraulic conductivity have been identified. As a result, the name Floridan Aquifer has evolved into "Floridan aquifer system", which contains the Upper and Lower Floridan aquifers.Williams, L.J., and Kuniansky, E.L., 2015, Revised hydrogeologic framework of the Floridan aquifer system in Florida and parts of Georgia, Alabama, and South Carolina: U.S. Geological Survey Professional Paper 1807, 140 p., 23 pls., (https://pubs.usgs.gov/pp/1807/)
Withdrawals from the Floridan aquifer system began in 1887 when the city of Savannah, Georgia, began to supplement surface water withdrawals from the Savannah River with groundwater. At that time artesian heads in the system were above land surface, and no pumps were needed; by 1898, it was estimated that between 200 and 300 wells had been finished in southern Georgia, and by 1943 about 3,500 wells had been completed in the six coastal counties of Georgia. By around 1910, development of the Floridan aquifer system had already occurred in Fernandina and Jacksonville and south along the east coast of Florida, as well as from Tampa south to Fort Myers on the west coast. Over time, the number of wells increased, as did the finished depths, as demand increased. Industrial supply for pulp and paper mills became a large proportion of the water withdrawn starting in the late 1930s. In the 1950s, all municipal, domestic, and industrial supply (except cooling), and about half of agricultural supply in Orlando had been converted to groundwater from the Floridan aquifer system. Groundwater withdrawals increased steadily from 630 Mgal/d () in 1950 to 3,430 Mgal/d () in 1990. Permitting and regulations enacted during the 1990s curtailed the year-on-year increases in withdrawal; however, withdrawals in 2000 increased to 4,020 Mgal/d () due to extreme drought conditions between 1999 and 2001 that prevailed over much of the southeastern United States. Much of the increase was for agricultural demand.Miller, J.A., 1986, Hydrogeologic framework of the Floridan aquifer system in Florida and in parts of Georgia, South Carolina, and Alabama: U.S. Geological Survey Professional Paper 1403-B, 91 p., https://pubs.er.usgs.gov/publication/pp1403B
Location
The Floridan aquifer system spans an area of about in the southeastern United States and underlies all of Florida and parts of southern Alabama, southeastern Georgia, and southern South Carolina. The Upper Floridan aquifer contains freshwater over much of its extent, though it is brackish with increasing salinity south of Lake Okeechobee.
The Floridan aquifer system crops out in central and southern Georgia where the limestone and its weathered byproducts are present at land surface. The aquifer generally dips below the land surface to the south where it becomes buried beneath surficial sand deposits and clay. In areas depicted in brown in the image at the right, the aquifer crops out and is again exposed at land surface. These regions are particularly prone to sinkhole activity due to the proximity of the karstified limestone aquifer to land surface.Florida sinkhole at Mosaic fertilizer site leaks radioactive water, September 17, 2016Land O'Lakes sinkhole deepens slightly, now stable, July 15, 2017 Some of the fractures/conduits within the aquifer are large enough for scuba divers to swim through.Underwater Archaeology Photos by Wes Skiles: Diepolder CaveWater's Journey: Hidden Rivers of Florida, Part 1 of 3
Hydrology and geology
The carbonate rocks that form the aquifer are of late Paleocene to early Oligocene age and are overlain by low-permeability clays of Miocene age (upper confining unit) and surficial sands of Pliocene and Holocene age (surficial aquifer system). In west-central Florida, northern Florida, and along the updip margin of the system, the limestone crops out and the aquifer system is unconfined. Where low-permeability clays of the upper confining unit are present and substantial, the system is confined and groundwater is contained under pressure. The upper confining unit is particularly thick in coastal Georgia and south Florida; downward leakage of water through the upper confining unit in these areas is minimal, and the aquifer system is thickly confined. Low permeability limestone rocks of Paleocene age (e.g. Cedar Keys Formation) form the base of the Floridan aquifer system. The aquifer ranges in thickness from less than in updip areas where the rocks outcrop to more than in southwestern Florida. Recharge, flow, and natural discharge are largely controlled by the degree of confinement provided by upper confining units, the interaction of streams with the aquifer in its unconfined areas, and the interaction between fresh and saline water along the coastlines.Williams, L.J., Dausman, A.D., and Bellino, J.C., 2011, Relation of Aquifer Confinement and Long-Term Groundwater-Level Decline in the Floridan Aquifer System, in Proceedings of the 2011 Georgia Water Resources Conference – University of Georgia, Athens, Ga., http://www.gwri.gatech.edu/sites/default/files/files/docs/2011/3.1.2_Williams_48.pdf
Where the system is at or near land surface (areas shaded brown in image above), clays are thin or absent, dissolution of the limestone is intensified, and many artesian springs and sinkholes are apparent. Transmissivity of the aquifer in karstified areas such as these is much higher owing to the development of large, well-connected conduits within the rock (see image at right). Springs form where the water pressure is great enough for the groundwater to flow out on the land surface. More than 700 springs have been mapped in Florida.Scott, T.M., Means, G.H., Meegan, R.P., Means, R.C., Upchurch, S., Copeland, R.E., Jones, J., Roberts, T., and Willet, A., 2004, Springs of Florida: Florida Geological Survey Bulletin 66, 677 p., http://aquaticcommons.org/1284/. For example, Wakulla Springs in Wakulla County has a flow rate of of water per day. A record peak flow from the spring on April 11, 1973, was measured at per secondequal to per day.
The system is composed of two main aquifers: the Upper Floridan aquifer and the Lower Floridan aquifer. These aquifers are separated by sediments that range from low-permeability clays in the panhandle (Bucatunna Clay) and low-permeability dolomites and gypsiferous anhydrite in west-central Florida to permeable limestones along the east coast of Florida and elsewhere. Where these intervening sediments and rock are permeable, the Upper and Lower Floridan aquifers behave as a single unit. Conversely, where the intervening sediments are less permeable, there is less hydraulic connection between the Upper and Lower Floridan aquifers.
Upper Floridan aquifer The Upper Floridan aquifer is the main source of water withdrawn from the Floridan aquifer system due to high yields and proximity to land surface. Groundwater is fresh in most areas, though locally may be brackish or saline, particularly in coastal areas with saltwater intrusion problems, and in South Florida. The Upper Floridan aquifer includes the uppermost or shallowest permeable zones in the Floridan aquifer system. In the northern half of the study area, this aquifer behaves as a single hydrogeologic unit and is undifferentiated. In the southern half of the study area, including most of central and southern Florida, the aquifer is thick and can be differentiated into three distinct zones, namely the uppermost permeable zone, the Ocala Lower-Permeability Zone, and the Avon Park Permeable Zone.