Browsing by Author "Zheng, Chunmiao"
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Item Application of phosphate and surfactant-modified zeolite for remediation/attenuation of trace elements in soil and coal fly ash(University of Alabama Libraries, 2012) Neupane, Ghanashyam; Donahoe, Rona Jean; University of Alabama TuscaloosaThis dissertation presents results of a research work aimed at understanding and addressing trace element contamination sourced by coal fly ash and arsenic trioxide herbicide. Both alkaline and acidic fly ash samples were found to contain significant concentrations of environmentally available trace elements. The treatment of fly ash leachate with surfactant-modified zeolite (SMZ) decreased the mobility of several trace elements. In general, up to 30% of the As, Mo, and V; up to 80% of the Cr; and up to 20% of the Se and Sr were removed from the leachate after SMZ treatment. Batch experiments, surface complexation modeling, and X-ray spectroscopic tools were used to elucidate the kinetics and mechanisms of arsenate (As(V)) and phosphate (Pi) adsorption on ferric hydroxide. Both oxyanions showed similar adsorptions during single-ion adsorption experiments; however, As(V) was preferentially adsorbed during competitive adsorption experiments. Similarly, more As(V) was adsorbed when it was loaded in sequence in Pi-equilibrated system than vice versa. Both oxyanions competed for adsorption on ferric-hydroxide and each of them showed a limited capacity to desorb the other, and relatively, more pre-equilibrated Pi was desorbed by sequentially added As(V) than vice versa. The As K-edge EXAFS analysis indicated the presence mononuclear and binuclear bidentate As(V) surface complexes. The Fe coordination numbers (CN) of these complexes increased with increasing time and decreased with addition of Pi into the system. Finally, an arsenic-contaminated soil collected from an industrial site located in the southeastern United States was amended with Pi and Ca to precipitate the arsenic as As-bearing apatite-like minerals. Phosphoric acid amendment of the soil with simultaneous addition of Ca dramatically decreased the mobility of soil As to near zero at pH > 6. Characterization of precipitate separated from the Ca-Pi treated soil by X-ray diffraction indicated that a carbonate-apatite mineral was formed in the soil and likely incorporated As(V) into its structure. The low solubilities of many of the Ca-Pi-As(V) minerals suggest that Ca-Pi treatment has promise as an effective, long-term method for in situ chemical fixation of As in contaminated soils and wastewaters.Item Assessment of Groundwater Susceptibility to Non-Point Source Contaminants Using Three-Dimensional Transient Indexes(MDPI, 2018) Zhang, Yong; Weissmann, Gary S.; Fogg, Graham E.; Lu, Bingqing; Sun, HongGuang; Zheng, Chunmiao; Hohai University; University of Alabama Tuscaloosa; University of New Mexico; University of California Davis; Southern University of Science & TechnologyGroundwater susceptibility to non-point source contamination is typically quantified by stable indexes, while groundwater quality evolution (or deterioration globally) can be a long-term process that may last for decades and exhibit strong temporal variations. This study proposes a three-dimensional (3-d), transient index map built upon physical models to characterize the complete temporal evolution of deep aquifer susceptibility. For illustration purposes, the previous travel time probability density (BTTPD) approach is extended to assess the 3-d deep groundwater susceptibility to non-point source contamination within a sequence stratigraphic framework observed in the Kings River fluvial fan (KRFF) aquifer. The BTTPD, which represents complete age distributions underlying a single groundwater sample in a regional-scale aquifer, is used as a quantitative, transient measure of aquifer susceptibility. The resultant 3-d imaging of susceptibility using the simulated BTTPDs in KRFF reveals the strong influence of regional-scale heterogeneity on susceptibility. The regional-scale incised-valley fill deposits increase the susceptibility of aquifers by enhancing rapid downward solute movement and displaying relatively narrow and young age distributions. In contrast, the regional-scale sequence-boundary paleosols within the open-fan deposits protect deep aquifers by slowing downward solute movement and displaying a relatively broad and old age distribution. Further comparison of the simulated susceptibility index maps to known contaminant distributions shows that these maps are generally consistent with the high concentration and quick evolution of 1,2-dibromo-3-chloropropane (DBCP) in groundwater around the incised-valley fill since the 1970s'. This application demonstrates that the BTTPDs can be used as quantitative and transient measures of deep aquifer susceptibility to non-point source contamination.Item Coseismic and postseismic deformation of the great 2004 Sumatra-Andaman Earthquake(University of Alabama Libraries, 2011) Hughes, Kristin; Masterlark, Timothy; University of Alabama TuscaloosaThe 26 December 2004 M9.2 Sumatra-Andaman earthquake (SAE) induced a devastating tsunami when it ruptured over 1300 km of the boundary between the Indo-Australian plate and Burma microplate (Vigny et al., 2005; Bilek, 2007). Three months later on 28 March 2005, the M8.7 Nias earthquake (NE) ruptured over 400 km along the same trench overlapping and progressing to the south of the M9.2 rupture (Banerjee et al., 2007). The spatial and temporal proximity of these two earthquakes suggests that the SAE mechanically influenced the timing of the NE. I analyze the coseismic and postseismic deformation, stress, and pore pressure of the 2004 SAE using 3D finite element models (FEMs) in order to determine the mechanical coupling of the SAE and NE. The motivation for using FEMs is two-fold. First, FEMs allow me to honor the geologic structure of the Sumatra-Andaman subduction zone, and second, FEMs simulate the mechanical behavior of quasi-static coseismic and postseismic deformation systems (e.g., elastic, poroelastic, and viscoelastic materials). The results of my study include: 1) Coseismic slip distributions are incredibly sensitive to the distribution of material properties (Masterlark and Hughes, 2008), 2) Slip models derived from tsunami wave heights do not match slip models derived from GPS data (Hughes and Masterlark, 2008), 3) These FEMs predict postseismic poroelastic deformation and viscoelastic deformation simultaneously (Masterlark and Hughes, 2008), 4) Pore pressure changes induced by the SAE triggered the NE via fluid flow in the subducting oceanic crust and caused the NE to occur 7 years ahead of interseismic strain accumulation predictions (Hughes et al., 2010; Hughes et al., 2011), 5) Global Conductance Matrices provide a way to smooth an underdetermined FEM for arbitrarily irregular surfaces, and 6) FEMs are capable and desired to model subduction zone deformation built around the complexity of a subducting slab which is usually ignored in geodetic studies (Masterlark and Hughes, 2008; Hughes et al., 2010). Rapidly advancing computational capabilities recently placed FEMs at the forefront of earthquake deformation analyses. The results and conclusions of this study will strongly influence future analyses of coseismic and postseismic deformation, stress, pore pressure, and tsunami genesis.Item Evaluation of submarine groundwater discharge and groundwater quality using a novel coupled approach: isotopic tracer techniques and numerical modeling(University of Alabama Libraries, 2013) Ellis, John H.; Tick, Geoffrey R.; Dimova, Natasha T.; University of Alabama TuscaloosaIt has been recognized that submarine groundwater discharge (SGD) may be one of the principal pathways for delivering nutrients to surface water bodies, resulting in eutrophication of many nearshore coastal areas throughout the world. A one-year study of the coastal aquifer system (A1, A2, A3-Aquifers) of Gulf Shores, Alabama was conducted to assess SGD fluxes, characterize contaminant and nutrient transport through the aquifer system, and determine the availability of future aquifer resources. A three-dimensional density-dependent groundwater flow and transport model (SEAWAT), based on the coupling of MOFLOW and MT3DMS, was used to simulate the transport of nitrate and sulfate through the groundwater system to the coast. The model was refined and calibrated using independently determined field-based radon (222Rn, t1/2=3.82 d) isotopic tracer time-series surveys across a portion of the model area to enhance estimates of nearshore SGD. Two SGD approaches, integrated with 222Rn-determined seepage rates, were developed to determine (1) localized; and (2) entire-shoreline SGD. Thirty-two groundwater wells within the study area were sampled to constrain the groundwater 222Rn end-member in the model and characterize the extent of nutrient contamination. The ArcGIS database was used to spatially plot and interpret nutrient and 222Rn data, and generate iso-concentration maps detailing groundwater contamination and aquifer piezometric surfaces across the study area. Radon concentrations measured in groundwater from the shallow A1 and deeper A2 Aquifers were statistically identical, an indication that there is direct connection between the two systems. Elevated nitrate and sulfate concentration (up to 30 mg/L and 724 mg/L, respectively) were observed through active monitoring with zones of principal discharge identified in the lower A2 Aquifer. A groundwater seepage rate of 18.3 cm/day, calculated through the radon mass-balance model at a model area lake, was used to calibrate the numerical model surficial aquifer zone. Final shoreline seepage fluxes of 6.41 and 8.62 cm/day were determined from the results of both the multi-cell and shoreface numerical model simulation SGD approaches, respectively. The results of the two numerical SGD methods demonstrate good agreement with the 222Rn-derived methods, and provided an effective approximation technique that can be inexpensively duplicated in other similar shoreline areas.Item Groundwater flow dynamics and contaminant transport to coastal waters under low recharge conditions: regional-scale study of the aquifer system underlying southern Baldwin County, Alabama(University of Alabama Libraries, 2009) Murgulet, Dorina; Tick, Geoffrey R.; University of Alabama TuscaloosaThis study examined the influence of drought conditions and increased hydrological stresses on the groundwater system flow dynamics, submarine groundwater discharge, and nitrate transport and discharge to the Gulf of Mexico. The results of these studies demonstrate that current stresses on the aquifer have led to significant saltwater intrusion and or direct infiltration into fresh groundwater, especially within the upper aquifers of the region. The nitrate and chloride data analyses reveal the persistent presence of multiple nitrate impacted zones within the study area. Stable isotope data support the hypothesis that nitrate in the investigated aquifers originates from the nitrification of ammonium in soils from a mixture of sources ranging from fertilizer to sewer and/or manure and that denitrification, the breakdown of nitrates to nitrogen gas, is not significant in the investigated aquifer system. Furthermore, groundwater isotope data indicates that water in the aquifer system of the study area is most likely to have originated from precipitation and soil infiltration through relatively localized recharge and that the aquifer system in the study area is highly dynamic, experiencing mixing of recent recharged waters with older, ambient groundwaters. The presence of low residence times and the absence of denitrification reveal the oxic character of this system. As a proxy for a number of contaminant types, the groundwater flow and transport model was used to simulate nitrate transport in response to variable-density groundwater flow. The simulation results indicate that in the investigated aquifer system complexities arise because groundwater flow dynamics and contaminant transport are additionally influenced by density variations that can occur from the incursion of saltwater. The model predicts that the Beach Sand and Gulf Shores Aquifers will be impacted by severe saltwater intrusion whereas the deeper 350 and 500-Foot Aquifers will experience no saltwater intrusion for the entire simulation period. Consequently, nitrate discharge to the Gulf of Mexico originates from the lower part of the aquifer system through submarine groundwater discharge. This research will serve as a tool which may be applied to other similar coastal systems for more effective management strategies.Item High resolution molecular characterization of photochemical and microbial transformation of dissolved organic matter in temperate streams of different watershed land use(University of Alabama Libraries, 2014) Li, Xiaping; Lu, Yuehan; Zheng, Chunmiao; University of Alabama TuscaloosaThe objective of the present study was to provide better understanding of the effects of watershed land use on molecular composition of streamwater DOM and molecular transformations associated with photochemical and microbial processing of DOM. We compared DOM from headwater streams draining forest-dominated watersheds (FW) and pasture-dominated watersheds (PW) in the lower Chesapeake Bay region (Virginia, USA). Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry analysis was conducted on streamwater DOM prior to and after laboratory incubations: 1) bacteria-only incubations; 2) light-only incubations; and 3) combined light+bacterial incubations. Results showed that DOM in FW streams and PW streams differed in molecular characteristics--the former was characterized by greater structural complexity and aromaticity, higher proportions of condensed aromatic molecules and black carbon-like components, while the latter was higher in the proportions of lipid-like components, protein-like components and aliphatic compounds. Relative to DOM from FW streams, DOM from PW streams was more reactive to bacterial transformation. Protein-like components, lipid-like components and unsaturated hydrocarbon-like components are primarily responsible for the changes associated with bacterial transformation of DOM. However, similar behavior was also observed for DOM in FW streams and PW streams under the influence of bacterial and photochemical processes. Bacterial transformation reduced the proportions of lipid-like components but increased the proportions of lignin-like components and carboxyl-rich alicyclic molecule-like components, indicating that lipid-like components was a bioreactive class while lignin-like components and carboxyl-rich alicyclic were resistant to bacterial processing. Photochemical processes, alone or combined with microbial alterations, increased the proportions of protein-like components, which may be due to the light stimulation of autochthonous production of protein-like components, and increased the relative abundance of carboxyl-rich alicyclic molecule-like components, which indicates the refractory nature of these molecules. Photochemical processes also significantly reduced the amount of dissolved black carbon-like components, which suggests dissolved black carbon was a photoreactive class, countering the conventional view that black carbon was an inter group in carbon cycle. Collectively, these findings suggest that human land use in upstream watersheds may lead to alterations to the molecular composition of streamwater DOM as well as to its behavior to photochemical and microbial processing.Item Impact of elevated dissolved CO_2 on aquifer water quality(University of Alabama Libraries, 2015) Pugh, John David; Donahoe, Rona Jean; University of Alabama TuscaloosaCarbon capture and storage (CCS), specifically by means of geologic sequestration (GS), is a developing technology to reduce CO2 emissions to the atmosphere. This technology involves separating CO2 from flue gas and transporting the CO2 to underground storage locations that are isolated from the atmosphere. These storage locations are typically permeable and porous geologic formations that are not useful for any other purpose, such as drinking water. Geologic carbon sequestration operated at full-scale will require extensive performance monitoring, including potable groundwater monitoring. However, researchers and regulators do not fully understand what impact elevated CO2 levels would have on groundwater quality in the event that CO2 should leak into an overlying aquifer. The focus of the current study was to thoroughly characterize the properties of a typical Gulf Coast potable aquifer for purposes of performing a controlled CO2 release experiment and to construct coupled geochemical and transport models capable of predicting impacts from CO2 migration into a drinking water aquifer. The aquifer is a methanogenic environment composed primarily of quartz and feldspars, with minor or trace amounts of pyrite, mica, illite, smectite, and kaolinite. The formation water is dominantly Na-HCO3, consistent with the theory and PHREEQC modeling results that suggest aquifer freshening and ion exchange have played dominant roles in determining the present-day dissolved major ion composition. This study also presents the design and implementation of a closed loop pumping and injection system designed to simulate CO2 leakage into a test site aquifer. Process monitoring results indicated that the test was performed with minimal variation in key process parameters, including temperature, pressure and injectate pH. In situ instrumentation deployed in monitoring wells allowed continuous readings of groundwater pH and conductivity, which were critical parameters for evaluating the aquifer response to carbonation and acidification. Successful modeling simulation of the pH response using results from the aquifer testing program suggested that the test was implemented and monitored appropriately and that that future data interpretations and modeling of the field experiment were not compromised by test design. Test results showed that no constituent was mobilized in excess of US EPA maximum contaminant levels, but that many constituents (primarily major and minor cations) were released in a pulse-like response at levels above their baseline concentrations. Dissolution of trace carbonate and pyrite in the aquifer are hypothesized to have triggered cation exchange reactions, a dominant geochemical process affecting major and minor cation behavior in the aquifer. Overall, the test has shown that the migration of carbon dioxide into a drinking water aquifer can mobilize ions into solution, but at levels that may not exceed EPA MCLs under the field conditions tested for this specific system. Data presented here are potentially applicable to assessments across the Gulf Coast, where the potential for deep geologic carbon sequestration and continued reliance upon groundwater resources are high.Item Influence of flow regime on U(VI) sorption kinetics in fine sediments at the Hanford site, Washington, USA(University of Alabama Libraries, 2012) Moser, Jessa V.; Zheng, Chunmiao; University of Alabama TuscaloosaThe effect of flow rate on U(VI) sorption kinetics was investigated by a series of column tests using the reactive mass fraction (<2mm) of sediments from the 300 Area in Hanford, WA. Three sets of constant flow rates subject to multiple stop flow events were employed to obtain U(VI) breakthrough curves at the column outlet. A lognormal distributed multi-rate surface complexation model was used to match the experimental breakthrough curves and calibrate the parameters of the multi-rate distribution. The results from the column tests clearly show that the mean of the lognormal distributed sorption rate constants increase with the flow rate, while the standard deviation of the lognormal distributions decreases with the flow rate. This finding is the first empirical evidence for the flow rate dependence of the multi-rate sorption kinetics and is thus of fundamental importance for future efforts to further improve the predictive modeling and remediation of U contamination.Item Integrated modeling and management of groundwater and surface water, zhangye basin, northwest China(University of Alabama Libraries, 2016) Huang, Li; Zheng, Chunmiao; University of Alabama TuscaloosaThis dissertation consists of three self-contained, yet closely related, papers summarizing the results of a comprehensive study aimed at the development of a decision support system for sustainable water resources management for the Zhangye Basin in northwestern China. The first paper presents a 3D groundwater flow model to represent groundwater dynamics of the basin from 1999 through 2010 using MODFLOW-2005. The regional 3D groundwater model provides reliable information of the flow field and produces detailed water budgets for management purposes. It defines the intensive groundwater-surface water interaction zones, and reveals the increasing flux exchange due to both climate change and human activities. The second paper presents an integrated 3D groundwater-surface water flow model using GSFLOW. The model calibration was done by first running PRMS and MODFLOW-2005 models separately, and then followed by the calibration of the integrated GSFLOW model. The model shows a detailed trend of water storage changes and their relationship with each inflow and outflow item. More importantly, this study demonstrates the applicability of integrated basin-scale models in characterizing the groundwater-surface water(GWSW) interaction, reproducing the flow system, and supporting sustainable water resources management while accounting for the effects of climate change in arid inland river basins. The third paper presents an efficient decision support tool, taking into consideration the relevant complexities and interactions in different water resource components, to inform decision making for water resources management for the Zhangye basin. On the basis of data collection and data mining, incorporated with integrated hydrological conceptual models and numerical models, a Bayesian network (BN) has been developed and calibrated by K-fold cross validation. The trained BN model captures the important hydrological cycle characteristics and uncertainty of related factors to provide the optimal management solutions under consideration. While this study is based on the Zhangye basin, the concepts and approaches developed in this study are of general applicability. The integrated GWSW modeling, coupled with a BN construct, provides an innovative tool to inform decision making in water resources management.Item Investigation of natural weathering processes and artificial treatment techniques in the attenuation of toxic metals from coal fly ash(University of Alabama Libraries, 2010) Bhattacharyya, Sidhartha; Donahoe, Rona Jean; University of Alabama TuscaloosaCoal fly ash contains high levels of hazardous trace elements such as As, B, Cr, Mo, Ni, Se, Sr and V, which may have a negative impact on the environment due to potential leaching by acid rain and groundwater. This study seeks to develop new fly ash management techniques by determining the effects of natural weathering on trace element mobility in fly ash and by evaluating the potential use of surfactant-modified zeolite and ferrous sulfate treatment for attenuating the mobility of trace elements associated with fly ash. The effects of weathering on trace element mobility in fly ash were studied using batch competitive adsorption experiments. Fresh fly ash shows high adsorption capacity for As, V and Mo, while weathered fly ash shows high affinity for Ni, Sr, As and V. Both fresh and weathered fly ash show low adsorption capacity for Se and B. Weathering reduced the adsorption capacities of fresh fly ash for As, B, Cr, Mo, Se and V, indicating increased mobility in ash disposal environments. The effectiveness of surfactant-modified zeolite (SMZ) as a PRB material was studied using batch experiments under competitive adsorption conditions. The results showed that SMZ preferably adsorbed V, Mo and Cr over As and Se. Unmodified zeolite (UMZ) showed high adsorption capacities for Ni and Sr. Both SMZ and UMZ failed to remove B from solution. The use of SMZ as a PRB material in coal fly ash management will be limited by its low affinity for B as well as its relatively low affinity for As, Se and cations. Ferrous sulfate treatment of coal fly ash successfully reduced the mobility of oxyanionic trace elements. The unbuffered 1:30 FS treatment was highly successful; oxyanion mobility reductions were: As (24-91%), Cr (82-97%), Mo (79-100%), Se (41-87%) and V (55-100%). On the other hand, the 1:30 FS fly ash treatment failed to reduce the mobility of B, Ni and Sr. Ferrous sulfate treatment is cost effective and can be applied directly to fresh fly ash produced in electric power plants, as well as to the fly ash already placed in the ash disposal facilities.Item Pore scale study of crude oil distribution and interfacial processes in unconsolidated porous media: an application of synchrotron x-ray microtomography(University of Alabama Libraries, 2011) Ghosh, Jaydeep; Tick, Geoffrey R.; University of Alabama TuscaloosaA pore-scale study was conducted to determine model reservoir systems most amenable to oil recovery by investigating the behavior of three fractions of crude oil distribution and morphology in three types of porous media with increasing heterogeneity (in grain size distribution) during sequential surfactant flooding episodes. Multiple columns, packed with three types of sand, were established with residual saturations of light, heavy, and extra-heavy crude oil fractions, respectively. These columns were then flooded with anionic surfactant solution in various episodes. Synchrotron X-ray microtomography (SXM) was used to obtain high-resolution 3-D images before and after each surfactant flooding event. Results show homogeneous distributions of light and heavy oil fractions, as residual saturation conditions, within the homogeneous sand. Heterogeneous oil blob distributions were observed within the two higher heterogeneous porous media types. Oil blob distributions became more heterogeneous after surfactant flooding for all porous-media systems. Oil recovery was most effective from the homogenous sand (100% recovery) after 5 pore volumes (PVs) of flooding. Mildly-heterogeneous sand yielded a limited but consistent recovery after each flooding episode (23% and 43% recovery for light and heavy after 5-PV flood). The highly-heterogeneous sand showed greater recovery (42% and 16% for light and heavy) only after 5-PVs of flushing. SXM images effectively demonstrate trapping mechanism and mobilization of extra-heavy oil controlled by wettability of porous media. Homogeneous sand showed limited recovery (6%), whereas highly-heterogeneous sand showed consistent 20% recovery of extra-heavy oil after each flooding episode. Although spontaneous in-situ-stable-emulsion was formed in the mildly-heterogeneous sand, no recovery was attained due to the "jamin" effect after the 2-PV flood and 7% recovery after the 5-PV flood. In general, oil blobs within the homogeneous and mildly- heterogeneous sands showed an increase in total surface area, but a gradual reduction of total surface area within the highly-heterogeneous sand after each surfactant flood. This innovative and cutting-edge research, for the first time, implemented SXM technology to understand the pore scale processes affecting enhanced oil recovery techniques. The results of this study can be extremely beneficial to establish 3-D model for pore-scale displacement efficiency for various reservoir media systems.Item Recharge estimation and sustainability assessment of groundwater resources in the North China Plain(University of Alabama Libraries, 2011) Cao, Guoliang; Zheng, Chunmiao; University of Alabama TuscaloosaSustainable use of groundwater resources requires a comprehensive understanding of the groundwater flow system, including recharge mechanisms and system dynamics to quantify future availability and variability of groundwater resources in response to climatic conditions (recharge) and human activities (pumping). This dissertation explores sustainability issues in the North China Plain (NCP), a region plagued by one of the worst groundwater overuse and depletion problems globally. The dissertation is organized as three closely related but self-contained papers. The first paper describes the development of a regional, three-dimensional groundwater flow model, and its application in investigating the overall flow dynamics of the groundwater system across the NCP under both predevelopment and post-development conditions. The output from the groundwater model provides estimates of groundwater depletion rates over the post-development period, which average about 4 km^3/yr. Mean annual groundwater recharge of the overall plain, as estimated through calibration of the groundwater model is ~120 mm, which is in reasonable agreement with previously reported values based on the regional water balance method. Groundwater storage depletion, as estimated from groundwater level fluctuation data and from the numerical simulation is highly correlated with variations in precipitation. The numerical model makes it possible to integrate the available hydrologic data, providing a comprehensive approach to evaluate sustainability of groundwater resources in the NCP. The results show a severe imbalance between groundwater recharge and groundwater extraction (the primary discharge). Finally, some strategies that have been conducted towards more sustainable groundwater management in the NCP are discussed. In the work discussed in the second paper, as a way of mitigating the uncertainty inherent in specifying groundwater recharge as a calibration parameter (as commonly done in regional groundwater modeling), a simplified vertical one-dimensional unsaturated zone flow model was coupled with the regional three-dimensional saturated zone flow model. This allows more realistic simulation of the recharge process at the interface between the unsaturated and saturated zones. Soil hydraulic parameters were estimated using pedotransfer functions. Simulation over 12 years (1993¨C2008) was performed across the NCP. Simulated mean annual recharge ranges from ¡Ü360 mm in the piedmont area to ¡Ü260 mm in the middle and coastal plain areas, with a mean of ~150 mm across the NCP; this figure represents 18% of the average annual precipitation plus irrigation. Variability in soil texture and hydraulic properties is primarily responsible for the large range in simulated recharge rates. Increasing thickness of the unsaturated zone with groundwater depletion was shown to have little effect on long term mean groundwater recharge. The third paper discusses the application of direct simulation of groundwater mean age using a solute transport model to help calibrate the flow model parameters, including recharge rates. The simulated age distribution and the recalibrated flow model were then used to characterize the flow regime both under natural conditions and under conditions as altered by groundwater pumping. The model results indicate that simulated groundwater age in the NCP is affected both by the paleo-hydrologic conditions and by extensive groundwater pumping. Flow path analysis, water budget calculations, and the simulated groundwater age distribution all indicate that the lateral flow to the deep aquifer zone in the NCP is limited, and that the primary water input to the deep aquifer zone is downward leakage from the shallow aquifer zone; the extensive pumping of deep groundwater in recent decades has increased this downward flow. These results confirm that regional pumping has altered the flow regime in the deep aquifer zone, and that widely distributed vertical leakage has become a dominant process shaping the flow pattern both in the shallow and deep aquifers of the NCP.Item Simulating PFAS adsorption kinetics, adsorption isotherms, and nonideal transport in saturated soil with tempered one-sided stable density (TOSD) based models(Elsevier, 2021) Zhou, Dongbao; Brusseau, Mark L.; Zhang, Yong; Li, Shiyin; Wei, Wei; Sun, HongGuang; Zheng, Chunmiao; Hohai University; University of Arizona; University of Alabama Tuscaloosa; Nanjing Normal University; Southern University of Science & TechnologyReliable quantification of per- and polyfluoroalkyl substances (PFAS) adsorption and mobility in geomedia provides critical information (i.e., evaluation and prediction) for risk characterization and mitigation strategy development. Given the limited PFAS data available and various competing theories for modeling pollutant kinetics, it is indispensable to better understand and quantify the adsorption and transport of PFAS in geomedia using generalized models built upon a consistent physical theory. This study proposed a universal physical law (called the tempered stable law) in PFAS adsorption/transport by interpreting PFAS adsorption kinetics and nonideal transport as a nonequilibrium process dominated by adsorption/desorption with multiple rates following the tempered one-sided stable density (TOSD) distribution. This universal TOSD function led to novel TOSD-based models which were then tested by successfully simulating PFAS adsorption kinetics, adsorption isotherms, and nonideal transport data reported in the literature. Model comparisons and extensions were also discussed to further check the feasibility of the TOSD models and their adaptability to capture PFAS transport in more complex geomedia at all scales.Item Solute transport in aquifers characterized by small-scale preferential flowpaths: numerical modeling and field experimental studies(University of Alabama Libraries, 2010) Bianchi, Marco; Zheng, Chunmiao; University of Alabama TuscaloosaGroundwater flow and solute transport are affected by the connectivity of high hydraulic conductivity (K) sediments. This research used numerical modeling and field experiments to assess and quantify connectivity and to compare alternative transport models and approaches for representing connected heterogeneity. Field work was conducted at the well-known Macrodispersion Experiment (MADE) site to investigate transport hypothesized to be controlled by a network of highly connected preferential flow paths (PFP). The research results in three self-contained, closely related, papers. The first paper evaluates the ability of different transport models to reproduce the transport behavior in a synthetic 2-D aquifer system with a high-K network embedded in a low-K matrix. Results confirm that the classical Fickian advection-dispersion model (ADM) is unable to effectively reproduce solute transport unless heterogeneity is explicitly considered. Conversely, two non-Fickian models (dual-domain mass transfer and continuous-time random walk) are able to accurately match the transport behavior using only effective parameters. However, the continuous time random walk model requires a calibrated transport velocity that is physically unrealistic. The second paper investigates flow and transport connectivity in a small block of the MADE site aquifer. K values estimated from grain size analysis of 19 cores are used to generate 3-D conditional realizations of the K field. Anomalous transport in the generated K fields is revealed by particle tracking simulations and significant connectivity is quantified by a variety of connectivity indicators. Particle paths geometry shows that flow and transport connectivity do not require fully percolating high-K clusters. The third paper presents the results of new tracer test. Breakthrough curves measured at the extraction well and at 14 multilevel sampling ports along the vertical extension of the MADE site aquifer clearly reveal the presence of a complex network of PFPs. Numerical modeling based on experimental data shows that the dual-domain mass transfer model successfully captures the characteristics of the integrated breakthrough curve at the extraction well, but it is ineffective in reproducing the concentrations observed at the multilevel sampling locations, indicating that a high-resolution characterization of the aquifer heterogeneity would be needed to fully capture 3D transport details.Item Source, composition, and biodegradability of dissolved organic matter in the Parlung Zangbo river in southern Tibet, China(University of Alabama Libraries, 2019) Warren, Olivia Marie; Lu, Yuehan; Zheng, Chunmiao; University of Alabama TuscaloosaRegions of the Tibetan Plateau are experiencing increasing temperatures and decreasing glacial mass at a faster rate than the global average. Our study area, the Parlung Zangbo River basin, is within the southeastern region of the Tibetan Plateau which is experiencing the greatest degree of glacial mass loss. Glacial loss could mobilize organic matter from the terrestrial landscape to lakes and rivers and thereby influence watershed carbon cycles, water quality, and aquatic ecological functioning. However, the present-day dissolved organic matter (DOM) pool of the river, which could serve as a baseline for future predictions, has not been characterized. This project will characterize spatial distribution of the amount, source, and biodegradability of DOM exported from the Parlung Zangbo River basin. Samples were collected along the main stem of the river over 170 km, nearby tributaries, and a headwater lake and analyzed for DOC concentration and DOM quality based on absorbance and fluorescence properties. The excitation emission matrix coupled with parallel factor analysis (EEM-PARAFAC) yielded three humic-like fluorophores and two protein-like fluorophores. A subset of samples analyzed with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS) analysis showed that the DOM pool was dominated by lignins. Incubation experiments showed microbial utilization of DOM increased with increasing temperature up to an optimum temperature (between 17°C and 25°C) before declining. Lake samples showed characteristics indicative of glacial contribution, including greater proportions of Nitrogen-rich DOM and microbially-derived DOM, as well as higher β:α values that suggest lower degrees of diagenesis and higher bioreactivity. Our results suggest that increasing glacial loss in the future may shift the composition and increase the bioreactivity of DOM pool in Tibetan rivers. Consequently, these shifts in the DOM pool will contribute to global warming through a positive feedback loop.Item Using electrical resistivity tomography to calibrate seawater intrusion models along the Alabama Gulf Coast(University of Alabama Libraries, 2014) Coburn, Nathan L.; Dimova, Natasha T.; University of Alabama TuscaloosaNumerical models (e.g., MODFLOW/SEAWAT) are commonly used to quantify the extent and magnitude of seawater intrusion (SI). Since coastal communities must account for SI into local aquifers, numerical models can be an effective planning and management tool as coastal populations increase. While these models tend to be limited by the availability of hydrological data, uncertainty in these results can be substantially reduced through the integration of field geophysical measurements. Field measurements employing electrical resistivity tomography (ERT) were utilized to calibrate a density-dependent groundwater flow model for Gulf Shores, Alabama. Specifically, six independent ERT profiles were produced within a modeled area adjacent to a shallow lake and along the near-shore boundary. The ERT methods were employed to a depth of 95 meters, encapsulating two aquifer systems with previously identified SI concerns (Chandler et al, 1986; Murgulet and Tick, 2008). Results from the ERT deployments were compared to previously developed models' near shore density boundary constructed from local borehole data, then utilized to calibrate the model freshwater/saltwater mixing zone. Other geophysical investigations employing similar methodology (e.g. Time-Domain Electromagnetics) have been used to calibrate SI models and to explore the extent of SI in a number of coastal regions. This study expands upon previous research through the integration of a 3-D groundwater flow model with greater resolution ERT measurements to more accurately determine the extent of SI, and delineate the near shore freshwater/seawater boundary zone.Item Using linear inverse methods and finite element models to explore sensitivity to homogeneous elastic half-space assumptions in deformation models of the 2000 eruption of Hekla volcano, Iceland(University of Alabama Libraries, 2013) Compton, Sarah K.; Masterlark, Timothy; Hansen, Samantha E.; University of Alabama TuscaloosaOn February 26, 2000, the 12-day, 18th historic eruption of Hekla volcano in Iceland began with an explosive Subplinian eruptive column and pyroclastic basaltic flows fed by column collapses (Höskuldsson et al., 2007). Interferometric synthetic aperture radar (InSAR) captured the deformation pattern associated with the movement of a shallow fissure (i.e. dike) during the eruption (Ofeigsson et al., 2011). These data present the opportunity to use inverse methods to estimate parameters describing the behavior of the eruptive fissure (Fukushima et al., 2010, Anderson and Segall, 2011, Ofeigsson et al., 2011). I use the 2000 eruption of Hekla as an example in linear inversions that investigate the influence of topography and layered rock properties in 3-D finite element models (FEMs) on estimates of parameters associated with the fissure movement. FEMs are used for this study because they are the best type of model which allow for arbitrary geometric configurations of the domain and effectively satisfies the static elastic governing equations. The results of the study are: 1. FEMs of fissure movement are sensitive to a free-surface geometry representing topography but less sensitive to rock property distribution. 2. The estimated magnitude of each movement responds differently to unique inputs. Including topography increased estimates of strike-slip motion and decreased estimates of opening relative to a homogeneous elastic half-space model or a layered elastic half-space model. 3. Including topography directly into the model domain allows exploration of arbitrary dike geometry, such as a dike which changes strike, which is not possible with HEHS assumptions and topographic corrections, but is indicated in this study. The flexibility and power of FEMs far outweighs the computational burden they used to present. The results of this study will guide future modelers to required steps to build the most accurate and efficient model to estimate parameters related to fissure behavior during an eruption. These results can help elucidate the plumbing system of a volcano, including the relationship between processes in the magma chamber and in the conduit during an eruption. This can help geologists, volcanologists, and hazard assessment teams assemble more accurate eruption forecasts.