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Research about Upper Floridan aquifer

Source-linked reports with geographic coverage including Upper Floridan aquifer.

9 recordsLinked to original sources
USGS2019

Geology and biostratigraphy of the Upper Floridan aquifer in the greater Savannah region, Georgia and South Carolina

The Upper Floridan aquifer (UFA) of South Carolina, Georgia, Alabama, Mississippi, and Florida has been considered a regionally continuous stratigraphic sequence of Eocene to Miocene carbonate strata, with documented unconformities based on lithology and biostratigraphy. As part of an investigation of the regional subsurface geologic framework in the Atlantic Coastal Plain Province, three deep cores were drilled by the U.S. Geological Survey at Pineora, Effingham County, Georgia; Cockspur Island, Chatham County, Georgia; and Palm Dunes, Beaufort County, South Carolina. The age of the UFAbased on calcareous nannofossil biostratigraphy ranges from early Oligocene to early Miocene in Pineora, late Eocene to late Oligocene in Cockspur Island, and late Eocene to questionably Miocene in Palm Dunes. Thin section analyses identified eleven unique microfacies across the study area and suggests that the sediments were most likely transported by oceanic currents at the time of deposition. Disconformities are identified from the Pineora and Palm Dunes cores and channel incision is documented at the top of the UFA in the Palm Dunes core. This study 1) documents how existing formation and time stratigraphic boundaries cross hydrogeologic units, 2) shows the complex geologic nature of the Upper Floridan aquifer across a relatively limited area, 3) sets forth a better understanding of how lateral and vertical changes in the lithologic units of the UFA affect permeability and porosity, and thus subsurface hydrologic flow, across the region, and 4) highlights the problems faced by legislators when implementing groundwater use regulations intended to slow salt water intrusion and drawdown.

Georgia, South Carolina↗
USGS2013

Simulated effects of Lower Floridan aquifer pumping on the Upper Floridan aquifer at Pooler, Chatham County, Georgia

A revised regional groundwater-flow model was used to assess the potential effects on the Upper Floridan aquifer (UFA) of pumping the Lower Floridan aquifer (LFA) from a new well (35Q069) located at the City of Pooler in coastal Georgia near Savannah. The spatial resolution of the original regional, steady-state, groundwater-flow model was increased to incorporate detailed hydrogeologic information resulting from field investigations at Pooler and existing wells in the area. Simulation results using the U.S. Geological Survey finite-difference code MODFLOW indicated that long-term pumping at a rate of 780 gallons per minute (gal/min) from the LFA well 35Q069 would cause a maximum drawdown of about 2.52 feet (ft) in the UFA (scenario A). This maximum drawdown in the UFA was greater than the observed draw-down of 0.9 ft in the 72-hour aquifer test, but this is expected because the steady-state simulated drawdown represents long-term pumping conditions. Model results for scenario A indicate that drawdown in the UFA exceeded 1 ft over a 163-square-mile (mi 2 ) area. Induced vertical leakage from the UFA provided about 98 percent of the water to the LFA; the area within 1 mile of the pumped well contributed about 81 percent of the water pumped. Simulated pumping changed regional water-budget components slightly and redistributed flow among model layers, namely increasing downward leakage in all layers, decreasing upward leakage in all layers above the LFA, increasing inflow to and decreasing outflow from lateral specified-head boundaries in the UA and LFA, and increasing the volume of induced recharge from the general head boundary to outcrop units. An additional two groundwater-pumping scenarios were run to establish that a linear relation exists between pumping rates of the LFA well 35Q069 (varied from 390 to 1,042 gal/min) and amount of drawdown in the UFA and LFA. Three groundwater-pumping scenarios were run to evaluate the amount of UFA pumping (128 to 340 gal/min) that would produce maximum drawdown in the UFA equivalent to that induced by pumping the LFA well 35Q069 at rates specified in scenarios A, B, and C (390 to 1,042 gal/min). Scenarios in which the LFA well 35Q069 was pumped produced a larger drawdown area in the UFA than scenarios in which the UFA well was pumped to offset the maximum UFA drawdown simulated by scenarios A, B, and C. Three additional groundwater-pumping scenarios were run to evaluate the combination of pumping reductions at existing Pooler UFA public-supply wells with the addition of pumping from the new LFA well. For each scenario, LFA well 35Q069 was pumped at different rates, and pumping at existing Pooler supply wells, located about 3.7 miles northward, was reduced according to UFA drawdown offsets (128 to 340 gal/min) established by scenarios D, E, and F. Decreases in the magnitude and areal extent of drawdown in the UFA in response to pumping the LFA well were realized for scenarios that simulated drawdown offsets (reductions) for the existing UFA wells at Pooler when compared with the magnitude and extent of drawdown resulting from scenarios that did not simulate drawdown offsets for the existing UFA wells at Pooler (scenarios A, B, and C). The revised model was evaluated for sensitivity by altering horizontal and vertical hydraulic conductivity in layers 5 through 7 (Floridan aquifer system) for newly established hydraulic-property zones by factors of 0.1, 0.5, 2.0, and 10.0. Results of the sensitivity analysis indicate that horizontal and vertical hydraulic conductivity of the UFA and LFA are the most important parameters in model simulations. The least sensitive parameters were the horizontal and vertical hydraulic conductivity of the Lower Floridan confining unit; changes to these parameters had little effect on simulated leakage and groundwater levels. The revised model reasonably depicts changes in groundwater levels resulting from pumping the LFA at Pooler at a rate of 780 gal/min. However, results are limited by the same model assumptions and design as the original model and placement of boundaries and type of boundary used exert the greatest control on overall groundwater flow and interaquifer leakage in the system. Simulation results have improved regional characterization of the Floridan aquifer system, which could be used by State officials in evaluating requests for groundwater withdrawal from the LFA.

Georgia↗
USGS2011

Hydrogeology and water quality of the Floridan aquifer system and effects of Lower Floridan aquifer pumping on the Upper Floridan aquifer at Fort Stewart, Georgia

Test drilling, field investigations, and digital modeling were completed at Fort Stewart, GA, during 2009?2010, to assess the geologic, hydraulic, and water-quality characteristics of the Floridan aquifer system and evaluate the effect of Lower Floridan aquifer (LFA) pumping on the Upper Floridan aquifer (UFA). This work was performed pursuant to the Georgia Environmental Protection Division interim permitting strategy for new wells completed in the LFA that requires simulation to (1) quantify pumping-induced aquifer leakage from the UFA to LFA, and (2) identify the equivalent rate of UFA pumping that would produce the same maximum drawdown in the UFA that anticipated pumping from LFA well would induce. Field investigation activities included (1) constructing a 1,300-foot (ft) test boring and well completed in the LFA (well 33P028), (2) constructing an observation well in the UFA (well 33P029), (3) collecting drill cuttings and borehole geophysical logs, (4) collecting core samples for analysis of vertical hydraulic conductivity and porosity, (5) conducting flowmeter and packer tests in the open borehole within the UFA and LFA, (6) collecting depth-integrated water samples to assess basic ionic chemistry of various water-bearing zones, and (7) conducting aquifer tests in new LFA and UFA wells to determine hydraulic properties and assess interaquifer leakage. Using data collected at the site and in nearby areas, model simulation was used to assess the effects of LFA pumping on the UFA. Borehole-geophysical and flowmeter data indicate the LFA at Fort Stewart consists of limestone and dolomitic limestone between depths of 912 and 1,250 ft. Flowmeter data indicate the presence of three permeable zones at depth intervals of 912-947, 1,090-1,139, and 1,211?1,250 ft. LFA well 33P028 received 50 percent of the pumped volume from the uppermost permeable zone, and about 18 and 32 percent of the pumped volume from the middle and lowest permeable zones, respectively. Chemical constituent concentrations increased with depth, and water from all permeable zones contained sulfate at concentrations that exceeded the U.S. Environmental Protection Agency secondary maximum contaminant level of 250 milligrams per liter. A 72-hour aquifer test pumped LFA well 33P028 at 740 gallons per minute (gal/min), producing about 39 ft of drawdown in the pumped well and about 0.4 foot in nearby UFA well 33P029. Simulation using the U.S. Geological Survey finite-difference code MODFLOW was used to determine long-term, steady-state flow in the Floridan aquifer system, assuming the LFA well was pumped continuously at a rate of 740 gal/min. Simulated steady-state drawdown in the LFA was identical to that observed in pumped LFA well 33P028 at the end of the 72-hour test, with values larger than 1 ft extending 4.4 square miles symmetrically around the pumped well. Simulated steady-state drawdown in the UFA resulting from pumping in LFA well 33P028 exceeded 1 ft within a 1.4-square-mile circular area, and maximum drawdown in the UFA was 1.1 ft. Leakage from the UFA through the Lower Floridan confining unit contributed about 98 percent of the water to the well; lateral flow from specified-head model boundaries contributed about 2 percent. About 80 percent of the water supplied to LFA well 33P028 originated from within 1 mile of the well, and 49 percent was derived from within 0.5 mile of the well. Vertical hydraulic gradients and vertical leakage are progressively higher near the LFA pumped well which results in a correspondingly higher contribution of water from the UFA to the pumped well at distances closer to the pumped well. Simulated pumping-induced interaquifer leakage from the UFA to the LFA totaled 725 gal/min (1.04 million gallons per day), whereas simulated pumping at 205 gal/min (0.3 million gallons per day) from UFA well 33P029 produced the equivalent maximum drawdown as pumping LFA well 33P028 at 740 gal/min during the aquifer test. This equivalent pumpin

Georgia↗
USGS2005

Ground-water flow and water quality in the Upper Floridan aquifer, southwestern Albany area, Georgia, 1998-2001

During 1997, the Dougherty County Health Department sampled more than 700 wells completed in the Upper Floridan aquifer in Dougherty County, Georgia, and determined that nitrate as nitrogen (hereinafter called nitrate) concentrations were above 10 milligrams per liter (mg/L) in 12 percent of the wells. Ten mg/L is the Georgia primary drinking-water standard. The ground-water flow system is complex and poorly understood in this predominantly agricultural area. Therefore, the U.S. Geological Survey (USGS) - in cooperation with Albany Water, Gas and Light Commission - conducted a study to better define ground-water flow and water quality in the Upper Florida aquifer in the southwestern Albany area, Georgia. Ground-water levels were measured in the southwestern Albany area, Georgia, during May 1998 and March 1999 (spring), and October 1998 and September 1999 (fall). Groundwater levels measured in 75 wells open only to the Upper Floridan aquifer were used to construct potentiometric-surface maps for those four time periods. These maps show that ground water generally flows from northwest to southeast at gradients ranging from about 2 to greater than 10 feet per mile. During spring and fall 1998, ground-water levels were high and mounding of the potentiometric surface occurred in the central part of the study area, indicating a local recharge area. Water levels declined from December through February, and by March 1999 the mound in the potentiometric surface had dissipated. Of the 75 wells in the potentiometric network, 24 were selected for a water-quality network. These 24 wells and 1 spring were sampled during fall 1998 and spring 1999. Samples were analyzed for major chemical constituents, selected minor constituents, selected nutrients, and chlorofluorocarbons (CFC). Water-quality field measurements - such as water temperature, pH, specific conductance (SC), and dissolved oxygen (DO) - were taken at each well. During August 2000, a ground-water sample was collected and analyzed for selected sewage tracers. During March 2001, water samples from selected wells were analyzed for nitrogen and oxygen isotopes. Age-dating analysis using CFCs yield apparent groundwater ages that range from modern to greater than 50 years. The chemistry of ground water in the Upper Floridan aquifer varies widely throughout the southwestern Albany area, Georgia, and in general represents the chemistry commonly found in recharge areas. From fall 1998 through spring 1999, median values of pH, SC, and DO concentration were 7.6 standard units, 266 microsiemens per centimeter at 25 degrees Celsius (uS/cm), and 5.6 mg/L, respectively. The SC is highest (350 - 400 uS/cm) where mounding of the potentiometric surface exists. Specific DO concentrations indicate an area of anoxic ground water in the north-central part of the study area. Water samples indicate that ground water in the study area is dominated by calcium and bicarbonate ions, which is consistent with the limestone lithology of the aquifer. About 25 percent of the samples contained sodium and chloride at ratios similar to those in rainfall, indicating a close proximity to recharge areas. The remaining water samples, however, had sodiumchloride ratios less than 0.90, the ratio in Tift County, Georgia, rainfall samples. These low sodium-chloride ratios are consistent with chloride enrichment. Minor constituent and nutrient concentrations typically are below laboratory reporting limits; however, the maximum nitrate concentration measured during the study period was 12.2 mg/L, and the median concentration for the study period was 3.0 mg/L. Samples collected during 1999 had a higher median nitrate concentration than the 1998 samples. Regression analysis indicated that nitrate concentrations are related exponentially to chloride concentrations. Four distinct groups of ground-water-quality samples, plus four unique samples, were identified using cluster analysis. Water-quality groups I and

Georgia↗
USGS1991

Geohydrology and evaluation of water-resource potential of the Upper Floridan aquifer in the Albany area, southwestern Georgia

In the Albany area of southwestern Georgia, the Upper Floridan aquifer lies entirely within the Dougherty Plain district of the Coastal Plain physiographic province, and consists of the Ocala Limestone of late Eocene age. The aquifer is divided throughout most of the study area into an upper and a lower lithologic unit, which creates an upper and a lower water-bearing zone. The lower water-bearing zone consists of alternating layers of sandy limestone and medium-brown, recrystallized dolomitic limestone, and ranges in thickness from about 50 to 100 feet. It is highly fractured, and exhibits well-developed permeability by solution features that are responsible for transmitting most of the ground water in the aquifer. Transmissivity of the lower water-bearing zone ranges from about 90,000 to 178,000 feet squared per day. The upper water-bearing zone is a finely crystallized-to-oolitic, locally dolomitic limestone having an average thickness of about 60 feet. Transmissivities in the upper water-bearing zone are considerably less than those in the lower water-bearing zone. The Upper Floridan aquifer is overlain by about 20 to 120 feet of undifferentiated overburden consisting of fine-to-coarse quartz sand and noncalcareous clay. A clay zone about 10 to 30 feet thick may be continuous throughout the southwestern part of the Albany area, and where present, causes confinement of the Upper Floridan aquifer and creates perched ground water after periods of heavy rainfall. The Upper Floridan aquifer is confined below by the Lisbon Formation, a mostly dolomitic limestone that contains trace amounts of glauconite. The Lisbon Formation is at least 50 feet thick in the study area, and acts as an impermeable base to the Upper Floridan aquifer. The quality of ground-water in the Upper Floridan aquifer is suitable for most uses; wells generally yield water of the hard, calcium-bicarbonate type that generally meets the U.S. Environmental Protection Agency's Primary or Secondary Drinking Water Regulations. The water-resource potential of the Upper Floridan aquifer was evaluated by compiling results of test drilling and aquifer testing in the study area, and by conducting computer simulations of the ground-water-flow system under the seasonal-low conditions of November 1985, and under conditions of pumping within a 12square-mile area located southwest of Albany. Results of test drilling, aquifer testing, and water-quality analyses indicate that, in the area southwest of Albany, geohydrologic conditions in the Upper Floridan aquifer, undifferentiated overburden, and Lisbon Formation were favorable for the aquifer to provide a large quantity of water without having adverse effects on the ground-water system. The confinement of the Upper Floridan aquifer by the undifferentiated overburden and the rural setting of the area of potential development decreases the likelihood that chemical constituents will enter the aquifer during development of the ground-water resources. Computer simulations of ground-water flow in the Upper Floridan aquifer, incorporating conditions for regional flow across model boundaries, leakage from rivers and other surface-water features, and vertical leakage from the undifferentiated overburden, were conducted by using a finite-element model for groundwater flow in two dimensions. Comparison of computed and measured water levels in the Upper Floridan aquifer for November 1985 at 74 locations indicated that computed water levels generally were within 5 feet of the measured values, which is the accuracy to which measured water levels were known. Water-level altitudes ranged from about 260 feet to 130 feet above sea level in the study area during calibration. Aquifer discharge to the Flint River downstream from the Lake Worth dam was computed by the calibrated model to be about 1 billion gallons per day; about 300 million gallons per day greater than was measured for similar low-flow conditions. The excess computed discharge was attributed partially to stream withdrawals for industrial use, non-reported use, and channel evaporation, but mostly to increased gradients and increased flow from the aquifer to the river than existed during calibration. Results from the calibrated finite-element model indicate that ground-water flow is dominated by inflow from regional-flow components to the west, north, and east of the study area, and by outflow to the Flint River downstream from the Lake Worth dam. Simulation results indicated that directions of ground-water flow were not changed appreciably by pumping at the November 1985 rates. However, vertical leakage from the undifferentiated overburden caused local deviations in the regional flow pattern. A sensitivity analysis that was performed on 18 hydrologic factors affecting the flow system in the Upper Floridan aquifer showed that computed water levels changed the most (were the most sensitive) in response to changes in hydraulic conductivity of the aquifer, vertical leakage coefficient and water level in the undifferentiated overburden, and stage of the Flint River downstream from the Lake Worth dam. Computed water levels were least sensitive to changes in well pumpage, flow across the northern boundary and from Lake Worth, the boundary coefficient for the Flint River downstream from the Lake Worth dam, and flow from Cooleewahee Creek. Simulations of six pumping scenarios in the area of potential development southwest of Albany showed that the Upper Floridan aquifer is capable of providing at least 72 million gallons per day from five locations (14.4 million gallons per day each) within this area without causing adverse affects on the flow system. The 72million-gallon-per-day scenario yielded a maximum drawdown of about 9.4 feet, which placed the water level in the Upper Floridan aquifer about 50 feet above the top of the lower water-bearing zone. Hence, the likelihood of aquifer dewatering, well interference, or sinkhole development from pumping as much as 72 million gallons per day from within the area of potential development is small. All pumping scenarios showed that about 81 percent of the ground-water pumpage was derived from regional flow that would have discharged to the Flint River downstream from the Lake Worth dam. The dominant ground-water-flow direction toward the Flint River was not changed and no induced recharge from the Flint River entered the potential-development area. Induced recharge from the undifferentiated overburden contributed to about 1.5 percent of the total volume pumped during the simulations.

Georgia↗
USGS1987

Hydrogeology, chemical quality, and availability of ground water in the Upper Floridan aquifer, Albany area, Georgia

Large withdrawals of groundwater in the 1500 sq mi Albany area of southwestern Georgia have lowered water levels in deep aquifers as much as 140 ft. This study was conducted to evaluate the development potential of the shallow Upper Floridan aquifer as an alternate source of groundwater, especially for public supply. The Upper Floridan stores and transmits large quantities of water, mainly in a zone of high permeability in the lower part of the aquifer. The transmissivity of the aquifer ranges from < 10,000 sq ft/day northwest of Albany, to as much as 150 ,000 sq ft/day south and southeast of Albany. Twenty-eight years of agricultural and industrial pumping has not produced a long-term decline of the water level in the Upper Floridan; the aquifer system remains at equilibrium. The Upper Floridan yields hard, calcium bicarbonate-type water but concentrations do not exceed State drinking water standards. In most of the study area , contaminants applied to or spilled on the land surface eventually can be expected to percolate through the overburden and reach the aquifer. Thus, it is important that wells be sited away from areas that have been used for the storage and disposal of potential contaminants and, probably to a lesser extent, the application of agricultural chemicals. In the area of greatest development potential east of the Flint River, wells may penetrate major groundwater conduits. By limiting drawdown during well development and during production, the likelihood of causing sinkholes to form can be minimized. Closed depressions, or sinks, throughout the Dougherty Plain probably are unsuitable as well sites, because (1) they are subject to flooding, (2) they collect water from upgradient areas and could concentrate potential contaminants, (3) water probably percolates through their bottoms and could transport contaminants into the aquifer, and (4) the depressions may overlie limestone cavities filled with sand or clay that could interfere with well yield, development, and production. (Author 's abstract)

Georgia↗