Thesis (Ph. D.)--Florida State University, 2004. / Advisor: Dr. David E. Loper, Florida State University, College of Arts and Sciences, Geophysical Fluid Dynamics Institute. Title and description from dissertation home page (viewed Jan 14, 2005). Includes bibliographical references.

Caves, the cornerstone feature of karst aquifers, are little understood in Florida. This dissertation, which analyzes the morphology, elevation, lithologic setting, and hydrology of caves in west-central Florida, demonstrates that the karst of the unconfined Floridan aquifer differs from the paradigm view of karst presented in modern geology textbooks. The differences reflect setting: eogenetic (west-central Florida) vs. telogenetic (conventional). Interpretations about the architecture of cavernous porosity in this dissertation come from detailed surveys (497 stations) of seven air-filled caves.The surveys reveal that solution cavities within the unconfined Floridan aquifer align along NE-SW and NW-SE fractures. The surveys further identify tabular zones of cavernous porosity that extend for tens of meters. Characteristic "plus-sign" passages occur at the intersection of solution-enlarged fractures and the tabular horizons. The caves, as surveyed, do not connect points of discrete aquifer input to springs. Rather, they are separated by intact bocks of aquifer matrix, ever- narrowing fissures, sediment fills, and breakdown. With an additional 574 spot elevations from 63 previously surveyed air-filled and submerged caves and 526 foot-length cavities encountered in 26 drilled wells, the assembled data reveal that cave passages above and below the watertable of the unconfined Floridan aquifer cluster at similar elevations throughout west-central Florida. At the largest scale, the levels of cavities cut across geologic structure, thus suggesting a water-table origin. The close linkage of the water table and sea level this coastal setting suggests the levels reflect positions of paleosea level. Given that the air-filled caves in west-central Florida reflect higher sea levels,the coastline would have been close when the air-filled caves formed. The levels organize according to a sea-level datum at elevations of 30 m, 20-22 m, 12-15 m,and 3-5 m. The levels are similar in elevation to nearby terraces evident in GIS and LIDAR topographic data. The terraces correspond to the classic, Quaternary marine terraces of the coastal plain of the southeastern U.S.A. Given that the now-submerged caves reflect lower sea levels, the coastline was far from the caves when they formed. They organize according to a watertable datum at depths of 15 m, 30-40 m, 60-70 m, and > 100 m with some correspondence to marine terrace and paleoshoreline features identified on the sea floor of the west florida shelf using GIS and multibeam bathymetry. The multigenerational origin of these deeper caves masks the correspondence. Although past water tables are seen to be the first-order control of cave passages regionally, lithology appears to play a significant role at the scale of an individual cave. Approximately 2,000 measurements of matrix permeability from more than 228 m of continuous core from the unconfined Floridan aquifer of west-central Florida reveal a wide-ranging facies-dependent matrix permeability[log k(m2)= -12.9 +/- 1.6, total range]. Solution passages tend to be wider where the matrix permeability is greater. Time-series analysis on measurements of spring discharge from 31 springs and published time series from 28 additional sites reveal key differences between eogenetic and telogenetic karst aquifers, reflecting the difference in matrix permeability of the eogenetic [log k(m2) from -14 to -11] and telogenetic[log k(m2) from -15 to -20] limestones. For instance, log Q/Qmin flow-duration curves have greater slopes at eogenetic karst springs, a manifestation of lowerratios between the maximum and mean discharge (Qmax/Qmean). Additionally,aquifer inertia as defined on auto correlograms is greater in eogenetic karst than telogenetic karst.Hydrographs of spring flow and water level vary on a seasonal or longertime scale. The localized, convective-style storm events typical of the Florida summer rainy season are not realized as individual peaks in these hydrographs.Apparently, large, widespread, storm events, such as hurricanes in the late summer and fall and frontal systems in the winter and spring, are necessary to produce significant changes in storage. Data from nine pressure transducers in caves and in the aquifer matrix across the unconfined Floridan aquifer all record immediate increases in the water level due to Hurricanes Frances and Jeanne in September of 2004. The increases are simultaneous over large regions. These changes do not propagate through the aquifer as a pulse like the classic scenario of conduit flow in telogenetic karst aquifers.

Aquifer storage and recovery (ASR) is a strategy in which water is injected into an aquifer when it is plentiful and pumped from the aquifer when water is scarce. An impediment to ASR in Florida is leaching of naturally-occurring arsenic from limestone of the Upper Floridan Aquifer System (UFAS) into stored water. The concentration of arsenic in surface water, which serves as the recharge water for many ASR systems, and native groundwater is usually much less than 3.0 µ/L. However, data from ASR wells in Florida show that arsenic in recovered water frequently exceeded the 10 µg/L maximum contaminant level (MCL) established by the Environmental Protection Agency and were as high as 130.0 µg/L. The cause of elevated arsenic concentrations is displacement of reduced native groundwater with oxygenated surface water that dissolves arsenic-bearing pyrite in limestone. Although arsenic can be removed from recovered water during final treatment, mobilization of arsenic in the aquifer at levels that exceed the MCL is problematic under federal regulations. This dissertation investigated a number of aspects of the ASR/arsenic problem to provide additional insights into the mechanisms of arsenic mobilization and measures that could be taken to avoid or reduce the release of arsenic during ASR operations. Chapter 2, involved development of a geochemical model to simulate an ASR system’s injection of oxygenated surface water into reduced groundwater to determine whether aquifer redox conditions could be altered to the degree of pyrite instability. Increasing amounts of injection water were added to the storage-zone in a series of steps and resulting reaction paths were plotted on pyrite stability diagrams. Unmixed storage-zone water in wells plotted within the pyrite stability field indicating that redox conditions were sufficiently reducing to allow for pyrite stability. Thus arsenic is immobilized in pyrite and its concentration in groundwater should be low. During simulation, as the injection/storage-zone water ratio increased, redox conditions became less reducing and pyrite became unstable. The result would be release of arsenic from limestone into storage-zone water. Chapter 3 examined the importance of maintaining a substantial volume of stored water around an ASR well to prevent recovery of reduced native groundwater to the vicinity of the well. Depleting the stored water and recovering reduced native groundwater would result in dissolution of arsenic-bearing hydrous ferric oxide (HFO) and release of arsenic into water recovered from the ASR well. Injection/recovery volumes for each cycle for each well were tracked to determine if a substantial volume of stored water was maintained for each cycle or if it was depleted so that reduced native groundwater was brought back to the well. Each well was assigned to either the “storage zone maintained group” where a zone of stored water was established in early cycles and largely maintained through the period of investigation, or the “storage-zone depleted group” where a zone of stored water was either established in later cycles and/or was depleted during the period of investigation. Graphical and statistical analyses verified that maximum arsenic concentrations for storage-zone maintained wells were nearly always lower in each cycle and declined below the MCL after fewer cycles than those of storage-zone depleted wells. Chapter 4 was a mineralogical investigation of cores located at 20 m (ASR core 1), 152 m (ASR core 2), and 452 m (ASR core 3) from operating ASR wells to determine where mobilized arsenic in limestone is precipitated during ASR. If arsenic is precipitated distally, reduced concentrations of elements in pyrite, (iron, sulfur, arsenic, etc.) would be expected in ASR core 1 relative to more distant cores and there would be noticeable changes in appearance of pyrite crystals due to enhanced oxidation. The results showed that mean concentrations of the elements were lowest in ASR core 2, which did not support distal precipitation. However, scanning electron microscopy identified well-defined pyrite framboids only in core 3 while framboids in ASR cores 1 and 2 were less clear and distinct, indicating pyrite oxidation in cores closest to ASR wells. Statistical comparison of concentrations of iron, sulfur, and arsenic between the three ASR cores and 19 control cores not subject to ASR, showed that mean concentrations in ASR cores 1 and 2 were statistically similar to concentrations in control cores. This indicated that concentrations in ASR cores 1 and 2 had not been significantly reduced by ASR. The concentrations of elements were higher in ASR core 3 than in ASR cores 1 and 2 and control cores and statistically dissimilar to all but one control core. This indicated natural heterogeneity in core 3 rather than diminution of elements in ASR cores 1 and 2 due to ASR. The statistical analysis supported local precipitation. Once arsenic is mobilized from dissolved pyrite, it is rapidly complexed with precipitated HFO near the well. As long as all of the stored water is not removed during recovery so that reduced native groundwater is brought back to the well, HFO remains stable and complexed with arsenic. The concentration of elements would not have been lowest in ASR core 1 for this reason and because calculations showed that the mass of arsenic removed during recovery events prior to coring was minor compared to the total in limestone surrounding the well. The implications of this are that while large quantities of arsenic are present near the ASR well, only a small percentage may be available for dissolution. Most arsenic occurs with pyrite in limestone, which may insulate it from exposure to oxidized injection water. Water recovered from ASR wells may continue to have low concentrations of arsenic indefinitely because as limestone is dissolved, more pyrite becomes exposed and available for dissolution. The primary contribution of this dissertation to understanding and overcoming the arsenic problem in ASR systems is the empirical data developed to support or challenge important ASR/arsenic hypotheses. These data were used to 1) establish that background concentrations of arsenic in groundwater of the Suwannee Limestone were less than 1µg/L, 2) demonstrate that redox conditions necessary for pyrite in limestone to become unstable and dissolve occur when oxygenated surface water is injected into the aquifer, 3) demonstrate that the concentration of pyrite in the Suwannee Limestone is spatially variable to a high degree, 4) support the hypothesis that following injection of oxygenated surface water, pyrite in limestone dissolves and releases arsenic into solution and HFO forms and complexes with the arsenic near the ASR well, 5) propose that only a small percentage of pyrite near an ASR well may be available for dissolution during each cycle because most occurs in the limestone matrix and is isolated from injection water, 6) propose that as a result of the previous conclusion, water recovered from ASR systems may continue to have low concentrations of arsenic indefinitely because as limestone that contains pyrite is dissolved with each cycle, additional pyrite is exposed and is available for dissolution, and 7) support the effectiveness of maintaining a zone of stored water in an ASR well as an effective means of minimizing arsenic in recovered water during ASR.

Ground water resources are heavily used for drinking water supply and often as a receptacle for waste water. One concern is the possible contamination of wetland areas by ground water receiving septic system infiltration. To investigate this, two tracer studies were performed using the bacteriophage PRD-1 by seeding septic systems adjacent to wetlands with the phage and monitoring migration towards wetland areas. Transport velocities were evaluated based on appearance of tracer in sampling wells at various distances from the injection point. Velocities were estimated to be 0.25 m/d and 0.4 m/d at the two sites. Some retardation with respect to the conservative tracer SF6 was observed, with a factor of about 1.5. Due to dry conditions, the water table was well below surface, so transport of the virus into surface water was not observed. Survival of public-health-related microorganisms in ground water is also a concern. The effects of temperature and total dissolved solids (TDS) on survival of 5 groups of indicator organisms were evaluated in controlled experiments. TDS did not have significant effects on inactivation of these microbes up to 1000 mg/l, but there was indication of reduced inactivation of enterococci at TDS concentrations of 3000 mg/l. Increased temperature consistently resulted in more rapid inactivation. Survival in aquifer and reservoir water samples was also evaluated, and significant effects due to water type, temperature, and pasteurization treatment were observed. Inactivation was more rapid in surface water sources, and pasteurization enhanced survival. For enterococci and DNA coliphage, pasteurization effects were more pronounced in surface water. DNA coliphage and perhaps fecal coliform appeared to be the more-conservative indicator organisms for aquifer injection monitoring. Lastly, it was observed that inactivation rates were considerably slower in pore water of saturated limestone than in the bulk water column of similar water sources and conditions, particularly for enterococci and fecal coliform.

Density-dependent groundwater flow in the Floridan aquifer system (FAS) depends on chloride concentrations and fluid temperature. Previous studies addressing the role of chloride concentration and temperatures on groundwater flow in the FAS have relied on observation data or simplified two-dimensional numerical models. A three-dimensional hydrologic analysis of FAS in peninsular Florida was performed using a modified version of SUTRA (SUTRA-MS) capable of simulating multi-species solute and heat transport. SUTRA-MS was developed during this investigation and is capable of reproducing results for several problems with known solutions.The model was developed using available geometric and hydraulic parameter data and calibrated using hydraulic head, chloride concentrations, and temperatures representative of conditions prior to significant groundwater pumpage from the FAS. The calibrated model is capable of reproducing observed pressures and temperatures but in general ov er-simulates chloride concentrations. The inability of the model to simulate observed chloride concentrations suggests chloride concentrations in the FAS are not in equilibrium with current sea level. Previous hydrologic studies of the FAS have attributed anomalous chloride concentrations to incomplete flushing of relict seawater that entered the aquifer during previous sea-level highstands.Three hypothetical, sinusoidal sea-level changes occurring over 100,000-years were used to evaluate how the aquifer responds to sea-level fluctuations. Model results indicate pressure equilibrates most rapidly and is followed by temperatures and then chloride concentrations. Confining unit thicknesses directly affect response times of pressure, temperature, and chloride concentrations in the FAS.Simulation of the system with ("geothermal case") and without ("isothermal case") the geothermal component reveals that the inflow of seawater from the Florida Straits would be similar without the heat f low but the distribution would differ significantly. The addition of heat flow also reduces the asymmetry of the circulation. Simulations evaluating aquifer responses to sea-level fluctuations and the thermal component indicate that the complicated three-dimensional setting of the FAS is a key component of the groundwater flow system and steady state conditions may not exist for relatively thick coastal aquifers that have experienced multiple sea-level cycles.

Title from PDF of title page. / Document formatted into pages; contains 322 pages. / Thesis (Ph.D.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: Ground water resources are heavily used for drinking water supply and often as a receptacle for waste water. One concern is the possible contamination of wetland areas by ground water receiving septic system infiltration. To investigate this, two tracer studies were performed using the bacteriophage PRD-1 by seeding septic systems adjacent to wetlands with the phage and monitoring migration towards wetland areas. Transport velocities were evaluated based on appearance of tracer in sampling wells at various distances from the injection point. Velocities were estimated to be 0.25 m/d and 0.4 m/d at the two sites. Some retardation with respect to the conservative tracer SF6 was observed, with a factor of about 1.5. Due to dry conditions, the water table was well below surface, so transport of the virus into surface water was not observed. Survival of public-health-related microorganisms in ground water is also a concern. / ABSTRACT: The effects of temperature and total dissolved solids (TDS) on survival of 5 groups of indicator organisms were evaluated in controlled experiments. TDS did not have significant effects on inactivation of these microbes up to 1000 mg/l, but there was indication of reduced inactivation of enterococci at TDS concentrations of 3000 mg/l. Increased temperature consistently resulted in more rapid inactivation. Survival in aquifer and reservoir water samples was also evaluated, and significant effects due to water type, temperature, and pasteurization treatment were observed. Inactivation was more rapid in surface water sources, and pasteurization enhanced survival. For enterococci and DNA coliphage, pasteurization effects were more pronounced in surface water. DNA coliphage and perhaps fecal coliform appeared to be the more-conservative indicator organisms for aquifer injection monitoring. / ABSTRACT: Lastly, it was observed that inactivation rates were considerably slower in pore water of saturated limestone than in the bulk water column of similar water sources and conditions, particularly for enterococci and fecal coliform. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

The Biscayne Aquifer is a primary source of water supply in Southeast Florida. As a coastal aquifer, it is threatened by saltwater intrusion (SWI) when the natural groundwater flow is altered by over-pumping of groundwater. SWI is detrimental to the quality of fresh groundwater sources, making the water unfit for drinking due to mixing and reactions with aquifer minerals. Increasing water demand and complex environmental issues thus force water utilities in South Florida to sustainably manage saltwater intrusion and develop alternative water supplies (e.g., aquifer storage and recovery, ASR). The objectives of this study were to develop and use calibrated geochemical models to estimate water quality changes during saline intrusion and during ASR in south Florida. A batch-reaction model of saltwater intrusion was developed and important geochemical reactions were inferred. Additionally, a reactive transport model was developed to assess fate and transport of major ions and trace metals (Fe, As) at the Kissimmee River ASR. Finally, a cost-effective management of saltwater intrusion that involves using abstraction and recharge wells was implemented and optimized for the case of the Biscayne Aquifer. Major processes in the SWI areas were found to be mixing and dissolution-precipitation reactions with calcite and dolomite. Most of the major ions (Cl, Na, K, Mg, SO4) behaved conservatively during ASR while Ca and alkalinity were affected by carbonate reactions and cation exchange. A complex set of reactions involving thermodynamic equilibrium, kinetics and surface complexation reactions was required in the ASR model to simulate observed concentrations of Fe and As. The saltwater management model aimed at finding optimal locations and flow rates for abstraction and recharge wells. Optimal solutions (i.e., minimum total salt and total cost Pareto front) were produced for the Biscayne Aquifer for scenarios of surface recharge induced by climate change-affected precipitation. In general, abstraction at the maximum rate near the coast and artificial recharge at locations much further inland were found to be optimal. Knowledge developed herein directly supports the understanding of SWI caused by anthropogenic stressors, such as over-pumping and sea level rise, on coastal aquifers.