Browsing by Subject "Environmental geology"

Arsenic (As) exposure via groundwater consumption is a global health problem affecting millions. Monitoring exposure is a key step in understanding and predicating future health outcomes. This thesis explores the relationships between arsenic concentrations in toenails and arsenic in water. Three case studies were investigated, with residents from: North Carolina, USA (n=103); the Rift Valley, Ethiopia (n=60); and the Mekong Delta, Vietnam (n=65). Arsenic concentrations above the WHO's recommended 10ppb limit were found in groundwater from the three research sites.

Arsenic in toenails was analyzed by inductively coupled plasma mass spectrometry (ICP-MS).

In the Rift Valley of Ethiopia, 53% of the tested drinking wells (n=34) had As above the WHO's limit. Arsenic concentrations in toenails (n=60) were significantly correlated to As concentrations in groundwater (r=0.72; p<0.001), reflecting the direct exposure of rural communities to As in well water, which is their principle water source. Male minors (<18 years old) were found to have greater nail-As concentrations compared with adults consuming equal amounts of As (p<0.05). Estimated As dose specifically from drinking water sources was also associated with nail concentrations (p<0.01).

In the Mekong Delta of Vietnam (Dong Thap Province), 36 out of the 68 tested wells had As content above the WHO's recommended limit of 10ppb, with levels as high as 981 ppb. Arsenic contents in nails collected from local residents (n=62) were significantly correlated to As in drinking water (r=0.49, p<0.001). Demographic and survey data show that the ratio of As in nail to As in water varies among residents that reflects differential As accumulation in the exposed population. The data show that water filtration and diet, particularly increased consumption of animal protein and dairy and reduced consumption of seafood, were associated with lower ratios of As in nail to As in water and thus could play important roles in mitigating As exposure.

Sixty-one wells were tested from Union County, North Carolina, with 15 out of 61 wells exceeded the WHO's 10 ppb limit. Arsenic values ranged from below the limit of detection (0.07) to 130ppb, with a mean of 11ppb (median=1.5ppb). Nails were collected from county residents (n=103) and were statistically correlated with As-water concentrations (r=0.48, p<0.001).

Integration of the data from the three cases studies across different populations and ethnicities show high correlation between As concentrations in groundwater and As in nails in all the three locations (r(Union County)= 0.48, p<0.001; r(Ethiopia)=0.72 p<0.001; r(Vietnam)=0.49, p<0.001). For As-nail to As-water pairs in which As in water was above 1ppb, these three locations are statistically indistinguishable from one another (r=0.62, p<0.001, n=176). These results support the hypothesis that nails can be used as a biomarker of exposure regardless of geographic or ethnic differences in populations considered. Nutrition (meat, seafood, and milk consumption) rather than gender, ethnicity, or dose is suggested to be the major confounding issue affecting the magnitude of As exposure in the human body.

This dissertation studies the chemo-hygro-mechanical coupling involved in the process of crack propagation encountered both in natural and engineered context. Chemical processes are likely to affect the mechanical properties of geo-materials, resulting in possible weakening effect. The deformation and micro-cracking induced by material weakening in turn enhances the overall mass removal. In this study, several models within both elasticity and plasticity domain are developed for a better understanding of the enhanced crack propagation. A deformational plasticity model based on experimental observations is addressed. Rigid-plasticity models are applied to various boundary conditions. In the chemo-elasticity model, chemical dissolution is assumed to be a function of a comprehensive strain invariant. One-way coupling and two-way coupling models are discussed. In the two-way coupling model, volumetric strain coupling and deviatoric strain coupling are compared. A variety of loading modes are adopted to investigate the chemical enhancement of propagation of a single crack. The behavior of the material is either rigid-plastic, or elastic with the variable of mass removal enters the constitutive equation as a chemical strain. Comparison between the results from two models is presented and discussed.

Groundwater is an increasingly important source of water for many parts of the world. Redox sensitive elements, like uranium, chromium, arsenic, and vanadium, are known to occur naturally in some groundwater systems, and may pose human health risks in populations that use groundwater as their major drinking water source. This dissertation characterizes factors affecting the occurrence of redox sensitive elements in different aquifer systems from different countries, including hydrogeology, geochemistry, and anthropogenic effects. It also addresses the co-occurrence of these elements in the groundwater resources, which may be associated with greater health risks than exposure to individual elements alone. The first three chapters of this dissertation focus on uranium occurrence in groundwater from different parts of India. Groundwater overexploitation has caused massive groundwater depletion and raised concerns for water and food security in India. Fieldwork in India combined with retrieving available data show that uranium is a widespread problem in groundwater across India, with concentrations greater than the World Health Organizations provisional guideline of 30 µg/L, mostly found in semiarid alluvial aquifers, as well as granitic and metamorphosed granitic crystalline aquifers. High concentrations of uranium in groundwater from the semiarid parts of Northwestern India is also associated with extensive agricultural activities. A detailed analysis, utilizing chemical (major and trace elements) and isotopic (δ18O, δ2H, δ11B, δ13C) data show that redox conditions, bicarbonate concentrations, and salinity have interconnected effects that control groundwater uranium concentrations, and that geochemical processes associated with irrigation under arid and semiarid conditions further intensify the groundwater uranium concentrations. An in-depth investigation of the groundwater chemistry from Rajasthan shows that in addition to uranium, groundwater used for drinking without any treatment contains multiple inorganic contaminants at levels that exceed both Indian and World Health Organization drinking water guidelines. The processes affecting Rajasthan's groundwater quality are common in many other groundwater resources from arid areas worldwide, and the lessons learned from evaluating the mechanisms that affect the groundwater quality in this study are universal and can be applied for other parts of the world. The last two chapters of this thesis address redox sensitive elements in groundwater form North Carolina, USA. Uranium, chromium, vanadium, and arsenic are all known to occur in North Carolina groundwater at health-relevant concentrations, with the highest concentrations of all elements occurring in fractured igneous and metamorphic formations from the Piedmont region. Arsenic occurs most frequently in suboxic to mixed redox character groundwater, whereas uranium, vanadium, and chromium occur mostly in oxic groundwater. Occurrences of arsenic, and to a lesser extent uranium, increase with pH, likely reflecting desorption from clay minerals on the aquifer rocks, while higher chromium and vanadium levels were measured in near-neutral pH and oxic groundwater, reflecting greater sensitivity to redox conditions. Due to similar geochemistry, vanadium and chromium co-occur most frequently. There is not enough health data to quantify the risks associated with such element co-occurrence, and there are large gaps between the current health recommendations and enforceable drinking water standards, especially for chromium given that hexavalent chromium, which is the predominant dissolved species of chromium in groundwater, is not regulated. The large complied dataset of measurments for chromium and hexavalent chromium in drinking water wells across North Carolina I demonstrate that most chromium in North Carolina occurs as the more toxic hexavalent chromium, presenting greater risks to human health. Several approaches to predicting chromium occurrence in NC groundwater are explored to help target future monitoring efforts and highlight areas of higher risks for occurrence and co-occurrence of these contaminants in groundwater resources of the Piedmont region of Eastern U.S.

Coal fired power plants are ubiquitous in the United States and most developed countries around the world, providing affordable electricity to consumers. In the US, approximately six hundred power plants generate 136 million tons of Coal Combustion Residuals (CCRs) annually, encompassing fly ash, bottom ash, and flue gas desulfurization materials. The range and blends of CCRs varies substantially across coal-fired plants and depends on a unique set of circumstances for each plant and coal source. Current U.S. regulations mandate the installation of advanced capture technologies to reduce atmospheric pollution, but do not address the transfer and storage, or the potential impacts to water resources. Thus improved air quality is traded for significant enrichments of contaminants in the solid waste and effluent discharged from power plants.

This work examines the geochemical and isotopic characteristics of CCRs, as well as potential environmental impacts from CCRs. This investigation looks at several different aspects of CCR and environmental interactions from 1) the immediate impacts of the 2008 TVA coal ash spill in Kingston, TN, 2) the long-term (18-month) exposure of the spilled ash in the Emory and Clinch rivers, 3) impacts on waterways in North Carolina that receive CCR effluent from coal fired power plants, and 4) examination of boron and strontium isotopes of CCRs from leaching experiments and their application as tracers in the environment of the TVA spill and NC waterways. These investigations have illuminated several conclusions, including contact of surface water with CCRs leach high concentrations of leachable CCR contaminants, such as As, Se, B, Sr, Mo, and V in the surface waters; the dilution effect is critical in determining the concentration of contaminants from the CCRs in surface water (both at the spill and in waterways receiving CCR effluent); recycling of trace elements (such as As) through adsorption/desorption can impact water quality; and elevated boron and strontium concentrations, in addition to their isotopes, can trace CCR effluent in the environment. Combining the geochemical behavior and isotopic characteristics provides a novel tool for the identification CCR effluents in the environment.

Fossil fuels continue to be a major component of the energy economies in North America, accounting for 60% of electricity generation in the U.S. Recent incidences (i.e. spills) and limited regulation of the fossil fuel industry has generated public concern about the risks fossil fuel development pose to water resources. Previous studies have identified negative impacts on water quality associated with the storage and disposal of coal combustion residuals, oil sands process-affected water, and oil and gas wastewater, as well as leaking of methane to groundwater in areas of hydraulic fracturing. In addition, contamination of water resources from natural (geogenic) sources has also been observed in many of the areas associated with fossil fuel development. Since naturally occurring saline water is common in some regions associated with fossil fuel explorations, delineating the effects of anthropogenic contamination sources is a major challenge for evaluating the impact of fossil fuel development on water quality.

This thesis investigates the geochemical and isotopic characteristics of wastewater from coal combustion residual storage ponds, unconventional oil and gas exploration, and oil sands mining, in an attempt to evaluate the use of geochemical and isotopic tracers to identify fossil fuel-associated wastewaters in the environment. This includes the investigation of (1) halogen (Br, I) and ammonium contents of oil and gas wastewater (OGW);(2) the lithium isotope ratios in OGW and coal combustion residuals; and (3) the inorganic geochemistry and boron, strontium and lithium isotope ratios of oil sands processed-affected water (OSPW). In three case studies, these geochemical and isotopic tools were integrated into comprehensive geochemical frameworks that investigated the (1) leaking of coal ash ponds to surface and groundwater in the southeastern United Sates; (2) geochemistry of groundwater in an area of shale gas development in West Virginia through time and space; and (3) evaluation of the sources of molybdenum in contaminated groundwater in southeastern

Wisconsin and possible links to coal ash surface disposal. These investigations illustrate a range of situations in which isotopic fingerprinting provided a unique geochemical tool that can successfully identify fossil fuel-related wastewater in the environment. These studies have also demonstrated the environmental impact upon releasing of fossil fuels wastewater to the environment. The case studies support the use of geochemical and isotope tools as robust methods to not only identify contamination of water resources by fossil fuel-related activities, but also to distinguish wastewater contamination from naturally occurring contamination in areas of fossil fuel development. These studies highlight the benefit of using a suite of geochemical tools when investigating water quality impacts.

Abstract

Legal and illegal gold mining in the Madre de Dios area cause several environmental concerns linked with mercury pollution and deforestation, which make hydrological and sediment transport processes central for any assessment of ongoing and future environmental impacts. This thesis addresses the problem of estimating flow and transport processes in the virtually ungauged Madre de Dios basin (Peru) to provide a first basis on which transport of mercury adsorbed on the sediment may be evaluated. The thesis first applies a recent method to derive the probability distribution of liquid and solid discharges to gauged basins in the Tropical Zone (Puerto Rico). This application allows the evaluation of the uncertainty associated with estimates of flow and transport pdf's. Once the iuncertainty is quantified, the same tool is applied to provide the first evaluation of the frequency distributions of discharge and sediment fluxes in the Madre de Dios area.

Coal combustion residuals (CCRs or coal ash), phosphate rocks and fertilizers, and leaded gasoline and lead-based paint represent major anthropogenic sources of metal and metalloid (i.e., metal(loid)) contaminants released to the environment. This dissertation aims to characterize the compositions of trace elements and radiogenic isotopes (Pb, Sr) of these anthropogenic sources and further explore their individual applicability and/or conjunctive utility with radioactive isotopes (228Ra, 226Ra, 137Cs, and 210Pb) in tracing the origin, timing, and impacts of metal(loid) contamination at various scales and in multiple environmental settings.The trace element compositions and isotopic signatures of Pb and Sr in fly ash originating from coals of different coal basins in the United States were characterized. In addition, an extended database of the Pb isotope fingerprints of coal and coal ash from China and India – the world’s top two coal producers and consumers – was established, combining newly measured values of coal and coal ash samples in this dissertation and data compiled from the literature. The results showed that (1) the Pb isotope signature of coal fly ash is distinctive from the isotope compositions of both the legacy anthropogenic Pb sources (i.e., leaded gasoline and lead-based paint) as well as natural Pb, which can be used for detecting fly ash contamination in the environment; (2) the 87Sr/86Sr ratio of bulk coal fly ash is distinctive from that of water-soluble fraction, which reflects the heterogenous distribution of Sr in fly ash and indicates the different uses of 87Sr/86Sr ratio for tracing its contamination in different environmental settings (i.e., terrestrial versus aquatic); and (3) the integrative use of trace elements, Ra isotopes (228Ra/226Ra), and Pb isotopes can further improve the detection of trace levels of coal fly ash dispersed in the environment. Through the integration of geochemical and isotopic tools (i.e., trace element distribution and 87Sr/86Sr ratio) with morphological and magnetic observations, this dissertation revealed the decades of historical and current unmonitored releases of coal ash and associated metal(loid) contaminants from the inadequate coal ash disposal units to the adjacent freshwater lakes across North Carolina (NC). The temporal distribution and evolution of coal ash contamination in the lake sediments were constructed by 137Cs- and 210Pb-based chronology techniques. The contributions of coal fly ash to the total Pb accumulation in the sediments of these contaminated lakes were quantified using a Bayesian-based Pb isotope mixing model, and the results suggested that regionally Pb contamination from fly ash can significantly outweigh the Pb input of atmospheric deposition (i.e., leaded gasoline) in the environment. Furthermore, the Pb isotope compositions of coal fly ash from China, India, and the U.S. were constrained and the fluxes of Pb associated with coal fly ash disposal in the three countries were estimated, laying the groundwork for future research on the impacts of coal ash on the Pb biogeochemical cycles at larger scales. Additionally, this dissertation reported the first set of data on the Pb isotope compositions along with rare earth elements and yttrium (REY) of phosphate rocks and fertilizers sourced from different regions and origins around the world. The geological imprints reflected in the geochemical and Pb isotopic fingerprints of the phosphate rocks were discussed and their potential utilizations and limitations in tracing phosphate-associated metal(loid) contamination in the environment were evaluated. This lays the groundwork for future local and regional studies on tracing the impacts of metal(loid) contaminants from phosphate rock mining and phosphate fertilizer application. Furthermore, this dissertation showcased a holistic assessment of the legacy anthropogenic contamination of Pb and other metal(loid)s in urban soils from Durham, NC, whereby fallout radionuclides 137Cs and 210Pb were proposed as potential indicators of the extent of soil disturbances that can impact the mobilization and redistribution of metal(loid) contaminants. The imprints of distinctive Pb isotopic fingerprints of leaded gasoline and lead-based paint in the soils reflected the persistent presence of these legacy sources in the urban environment of today, and the potential bioavailability of toxic metal(loid)s in the contaminated soils upon oral ingestion was assessed via in vitro arrays.