USGS Science⌕ Search

Geology topics

Research about Floridan aquifer

Source-linked reports with geographic coverage including Floridan aquifer.

8 recordsLinked to original sources
USGS2002

Variations in water levels and chloride concentrations in the Floridan aquifer system in Duval County, Florida

The Floridan aquifer system is the principal source of water supply in northeastern Florida. Increasing demands for water from the Floridan aquifer system in Duval County (fig. 1) have resulted in a need to evaluate changes in water levels and chloride concentrations. Rapid population growth in Duval County is creating an increasing demand for freshwater. In 1960, the population of Duval County was about 455,000 (Brown and others, 1986), and in 2000 it was estimated to be about 779,000. As population continues to increase, additional water supplies will be needed. Increases in pumpage to meet these demands will lower the potentiometric surface and increase the potential for the upward movement of saline water from deeper zones of the aquifer system (Spechler, 1994; and Phelps and Spechler, 1997). The increased demand for water from the Floridan aquifer system requires that this valuable resource be adequately managed. Information on the trends in the potentiometric surface and chloride concentrations in the Floridan aquifer system is necessary for proper planning and management. This map report, prepared in cooperation with the City of Jacksonville, depicts the altitude of the potentiometric surface of the Upper Floridan aquifer in Duval County, and shows trends in the potentiometric surface and in chloride concentrations in the Floridan aquifer system at selected locations. The information presented in this report includes: (1) graphs showing water use for Duval and adjacent counties from 1965 to 1999; (2) maps showing the altitude of the potentiometric surface of the Upper Floridan aquifer in Duval County for January-February 1960, September 1998, and May 1999; (3) a map showing changes in the potentiometric surface of the Upper Floridan aquifer from January-February 1960 to May 1999; (4) hydrographs showing long-term water levels of selected wells in Duval County; and (5) graphs showing chloride concentrations in water at selected wells in Duval County.

Florida↗
USGS1989

Geochemistry of the Floridan aquifer system in Florida and in parts of Georgia, South Carolina, and Alabama

The chemical quality of the ground water in the Floridan aquifer system is determined primarily by mineral-water interaction. However, some changes in water quality have been imposed by development, particularly near coastal pumping centers. A total of 601 chemical analyses, all from different wells, most completed in the upper part of the aquifer system, were used to describe the variations in water chemistry and to study the processes responsible for observed changes. The Floridan aquifer system is a vertically continuous sequence of Tertiary carbonate rocks that are of generally high permeability and are hydraulically connected in varying degrees. The rocks are principally limestone and dolomite, but they grade into limy sands and clays near the aquifer system's updip limits. Major minerals in the aquifer system are calcite, dolomite, and, locally, gypsum or quartz; minor minerals include apatite, glauconite, and clay minerals such as kaolinite and montmorillonite. Trace amounts of metallic oxides or sulfides are present in some areas. The aquifer system consists of the Upper and Lower Floridan aquifers, separated in most places by a less permeable confining unit that has highly variable hydraulic properties. Only the Upper Floridan aquifer is present throughout the study area. Freshwater enters the aquifer system in outcrop areas located primarily in central Georgia and north-central Florida. Discharge occurs chiefly to streams and springs and, to a lesser extent, directly into the sea. Most of the flow into and out of the system takes place where it is unconfined or where the upper confining unit is thin. Secondary permeability developed by dissolution of aquifer material is most prominent in these areas of dynamic flow. Dissolved-solids concentrations in water from the Upper Floridan aquifer generally range from less than 25 milligrams per liter near outcrops to more than 25,000 milligrams per liter along the coasts. The dominant cations in the ground water are Ca2+, Mg2+, and Na+; the dominant anions are HCO3-, Cl-, and SO42-, The concentration of Ca2+ is controlled primarily by calcite saturation. Concentrations of Mg2+, NA+, and Cl- are highest where mixing of freshwater and saltwater occurs. Concentrations of HCO3- reflect the control of calcite solubility. The concentration of SO42- is highest where gypsiferous rock units are present in the aquifer system. The major geochemical processes that occur in the Upper Floridan aquifer, based on water-quality maps and computations using a geochemical model, are (1) dissolution of aquifer minerals toward equilibrium, (2) mixing of ground water with recharge, leakage, or seawater, (3) sulfate reduction, and (4) cation exchange between water and aquifer minerals. Similar processes apparently control minor dissolved constituents, although quantification is difficult with the available data. Statistical tests of available nutrient data indicate that concentrations of N (nitrogen) species in unconfined recharge areas may be increasing over time; more detailed studies of all N species are needed to test this hypothesis, however. Data on trace metals, radionuclides, and man-made organic contaminants are limited. Available data indicate that most freshwater within the Upper Floridan is potable, but detection of pesticides in a few samples indicates that the system is susceptible to contamination from the land surface in some areas, particularly where its upper confining unit is thin or absent. Geochemical models were used to examine changes in major chemical elements along selected ground-water paths within the Upper Floridan aquifer. Water in the Upper Floridan aquifer can be categorized into four hydrochemical facies, whose exact distribution is determined by confined or unconfined conditions of the aquifer and by chloride concentrations. The reaction models are considered plausible based on available chemical, isotopic, and hydrologic information, and they

Alabama, Florida, Georgia, South Carolina↗
USGS1988

Ground-water hydraulics, regional flow, and ground-water development of the Floridan aquifer system in Florida and in parts of Georgia, South Carolina, and Alabama

The Floridan aquifer system is one of the major sources of groundwater supplies in the United States. This productive aquifer system underlies all of Florida, southeast Georgia, and small parts of adjoining Alabama and South Carolina, for a total area of about 100,000 square miles. About 3 billion gallons of water per day were withdrawn from the aquifer system in 1980, and in many areas the Floridan is the sole source of freshwater. The Floridan aquifer system is a sequence of hydraulically connected carbonate rocks (principally limestone with some dolomite) ranging in age generally from late Paleocene to early Miocene. The rocks vary in thickness from a featheredge where they crop out to more than 3,500 feet where the aquifer is deeply buried. The aquifer system generally consists of an upper aquifer and a lower aquifer separated by a lesspermeable confining unit of highly variable properties. In parts of north Florida and southwest Georgia, where little permeability contrast exists among the units, the Floridan is effectively one continuous aquifer. The upper and lower aquifers, named the Upper Floridan aquifer and the Lower Floridan aquifer, are defined on the basis of permeability and their boundaries locally do not coincide with those for either time-stratigraphic or rock-stratigraphic units. Overlying much of the Floridan aquifer system are low-permeability clastic rocks. The lithology, thickness, and integrity of these rocks determine the degree of confinement and influence the distribution of natural recharge, discharge, and ground-water flow in the Floridan. The permeability of the Floridan aquifer system is derived from small openings including fossil hashes and solution-widened joints as well as large cavernous openings in karst areas. Diffuse flow predominates where the small openings occur, whereas conduit flow may occur where large cavernous openings are. Transmissivities are highest (greater than 1,000,000 feet squared per day) in the unconfined karst areas of central and northern Florida. Lowest transmissivities (less than 50,000 feet squared per day) occur in panhandle Florida and southernmost Florida where the Upper Floridan aquifer is confined by thick clay sections. The hydraulic properties of the Lower Floridan aquifer are not well known; however, intervals of high transmissivity occur that have been attributed to paleokarst development. Springs, nearly all of which occur in unconfined and semiconfined parts of the Upper Floridan aquifer in Florida are the dominant feature of the Floridan flow system. Before ground-water development, spring flow and point discharge to surface-water bodies were about 88 percent of the estimated 21,500 cubic feet per second total discharge, or about 19,000 cubic feet per second. Diffuse upward leakage, which occurs primarily in confined areas, accounted for the remaining 12 percent or about 2,500 cubic feet per second. Most of the recharge necessary to sustain springflow and aquifer discharge to streams and lakes occurs relatively close to springs and areas of point discharge to surface-water bodies. Recharge to the Upper Floridan is highest, averaging 10-20 inches per year, in unconfined or semiconfined spring areas. The proximity of high recharge to high discharge implies a vigorous and well-developed shallow flow system in the unconfined and semiconfined parts of the Upper Floridan aquifer. Ground-water flow is very sluggish in the parts of the aquifer system that are deeply buried and tightly confined, primarily southeast Georgia and northeast Florida, south Florida, and far-west panhandle Florida. Discharge to springs, streams, and lakes is practically nonexistent in the tightly confined areas and natural discharge occurs almost exclusively by diffuse upward leakage through thick overburden. The regional flow system has not been appreciably altered by groundwater development. However, increasing pumpage that reached 3 billion gallons per day by 1980 has resulted in long-term regional water level decline of more than 10 feet in three broad areas: coastal Georgia, adjacent South Carolina, and northeast Florida; west-central Florida; and panhandle Florida. Saltwater encroachment as a result of pumping has occurred locally in coastal areas. Pumpage from the Upper Floridan aquifer is supplied primarily by reduction of natural discharge and by increased recharge rather than by depletion of aquifer storage. About 20 percent is from reduced discharge to springs, streams, and lakes, about 20 percent is from reduced upward leakage, and about 60 percent is from increased recharge. Compared to predevelopment conditions, discharge to springs, streams, and lakes is reduced by less than 5 percent, upward leakage is reduced by about 30 percent, and recharge is increased by about 12 percent. Total recharge and, therefore, discharge increased from a predevelopment rate of 21,500 cubic feet per second to about 24,100 cubic feet per second by 1980. A considerable area remains of the Floridan aquifer system where large ground-water supplies may be developed. This area is largely inland from the coasts and characterized by high transmissivity and minimal development prior to the early 1980's. The major constraint on future development probably is degradation of water quality rather than water-quantity limitations.

Alabama, Florida, Georgia, South Carolina↗
USGS1985

Water-supply potential of the Floridan aquifer in Osceola, eastern Orange, and southwestern Brevard counties, Florida

The city of Melbourne and adjacent areas in south Brevard County obtain their water supply from Lake Washington. As of 1982, the lake could provide a maximum of 15 million gallons per day but the projected need for the year 2000 is nearly three times that amount. As one alternative for a future water supply, this study investigated with a digital model, the potential yields of well fields completed in the Floridan aquifer. Seven pumping schemes were simulated with the digital model. Each simulation was made under steady-state conditions so that storage properties of the ground-water system were not included. The most advantageous area for ground-water development was in central Osceola County. Poor quality of water precluded locating a well field within Brevard County. If the ground-water alternative is chosen for the future supply, an observation well network is advisable to monitor head changes; chloride concentration trends east of the pumping centers; and chloride concentration trends in zones below the pumped zone.

Florida↗
USGS1982

Simulated effects of ground-water development on the potentiometric surface of the Floridan aquifer, west-central Florida

A digital model of two-dimensional ground-water flow was used to predict changes in the potentiometric surface of the Floridan aquifer, 1976 to 2000, in a 5,938-square-mile area of west-central Florida. In 1975, ground water withdrawn from the Floridan aquifer for irrigation, phosphate mines, other industries, and municipal supplies averaged about 649 million gallons per day. Rates are projected to increase to about 840 million gallons per day by 2000. The model was calibrated under steady-state and transient conditions. Input parameters included transmissivity and storage coefficient of the Floridan aquifer; thickness, vertical hydraulic conductivity, and storage coefficient of the upper confining bed; altitudes of the water table and potentiometric surface; and ground-water withdrawals. Simulation of May 1976 to May 2000, using projected combined pumping rates for municipal supplies, irrigation, and industry (including existing and proposed phosphate mines), resulted in a rise in the potentiometric surface of about 10 feet in Polk County, and a decline of about 35 feet in parts of Manatee and Hardee Counties. The lowest predicted potentiometric level was about 30 feet below sea level. Predicted declines for November 1976 to October 2000 were generally 5 to 10 feet less than those for May 1976 to May 2000. (USGS)

Florida↗