The behaviour of hydrocarbon fuels in contaminated groundwater systems is studied using a multicomponent reactive transport model. The simulated processes include residual NAPL dissolution, aerobic and anaerobic biodegradation with daughter-product transport, and transport of a reactive carrier with mixed equilibrium/kinetic sorption. The solution algorithm is based on a three-dimensional Galerkin finite element scheme with deformable brick elements and capacity for a free watertable search. Nonlinearities are handled through Picard iteration. Convergence is rapid for most applications and mass balance errors for all phases are minimal. The model is first applied to simulate a pilot scale diesel fuel dissolution experiment in which humic acid is used as a natural organic carrier to enhance dissolution and to promote biodegradation of the aqueous components. The pilot scale experiment is described by Lesage et al. (1995) and Van Stempvoort et al. (2000). The conceptual model includes 8 unique components dissolving from 500 mL of residual diesel fuel within a 3D saturated domain. Oxygen-limiting competitive aerobic biodegradation with a dynamic microbial population is also included. A mixed 2-site equilibrium/kinetic model for describing sorption of the carrier to the aquifer solids was adopted to reproduce the observed breakthrough of the humic acid and organic components. Most model parameters were obtained independently with minimal calibration. Batch sorption data were found to fit well at the pilot scale, however biodegradation and dissolution rates were not well known and had to be fitted. Simulations confirmed the observed 10-fold increase in effective solubility of trimethylnaphthalene, and increases on the order of 2-5 for methyl- and dimethylnaphthalene. The simulated plumes showed almost complete attenuation after 5 years, in excellent agreement with observed data. A sensitivity analysis showed the importance of carrier concentrations, binding coefficients, dissolution and biodegradation rates. Compared to a dissolution scenario assuming no carrier, the humic acid-enhanced dissolution case decreased the remediation time by a factor of about 5. The second application of the model involves simulating the effect of ethanol on the persistence of benzene in gasoline-impacted groundwater systems. The conceptual model includes a 4-component residual gasoline source which is dissolving at the watertable into a 3D aquifer. Comparisons are made between dissolved plumes from a gasoline spill and those from an otherwise equivalent gasohol spill. Simulations have shown that under some conditions, a 10% ethanol component in gasoline can extend the travel distance of a benzene plume by at least 150% relative to that from an equivalent ethanol-free gasoline spill. The increase is due to preferred consumption of oxygen by ethanol and a corresponding reduction in the biodegradation rate of benzene while the two plumes overlap. Because of differences in retardation however, the ethanol and benzene plumes gradually separate. The impact therefore becomes limited because oxygen rapidly disperses behind the ethanol plume and benzene degradation eventually resumes. A sensitivity analysis for two common spill scenarios showed that background oxygen concentrations, and benzene retardation had the most significant influence on benzene persistence. A continuous gasohol spill over 10 years was found to increase the benzene travel distance by over 120% and a pure ethanol spill into an existing gasoline plume increased benzene travel distance by 150% after 40 years. The results are highly relevant in light of the forthcoming ban of MTBE in California and its likely replacement by ethanol by the end of 2002.

Ethanol can affect the biodegradation of gasoline hydrocarbons in groundwater. High concentrations of ethanol can be toxic to subsurface microorganisms that are otherwise capable of degrading hydrocarbons, such as benzene, toluene, ethylbenzene and xylenes (BTEX). At lower concentrations, ethanol may hinder BTEX degradation through substrate competition and the depletion of inorganic nutrients (e.g., nitrogen and phosphorus), oxygen and other electron acceptors needed for BTEX degradation. A series of laboratory experiments were designed to study the effect of ethanol on aquifer microorganisms and on aerobic BTEX biodegradation. A microcosm experiment was conducted to investigate the effect of ethanol on the biodegradation of BTEX. Microcosms were set up with Borden aquifer material and groundwater in which oxygen and nutrients were not limited. These microcosms contained BTEX in combination with a range of ethanol concentrations. Under these favourable conditions, the presence of ethanol up to concentrations of 1.9% (v/v) (equivalent to 15000 mg/L) caused little inhibition of BTEX degradation. Further experiments were conducted to study the antimicrobial effects of higher concentrations of ethanol. Following exposure to ethanol concentrations of 25% (v/v) or higher, microbial activity and survival was significantly diminished. Results suggest that a high concentration ethanol slug will have a major impact on the microbial community but that there would likely be potential for recovery. The recovery potential was examined further in laboratory column experiments designed to simulate a dynamic field situation where a high ethanol pulse is followed by a BTEX plume. These column experiments were conducted with Borden aquifer material and groundwater under aerobic conditions. The concentration of the ethanol pulse was 25% (v/v), which was expected to significantly alter the microbial population without destroying it. Following the ethanol exposure, groundwater and BTEX were allowed to flow through one column to simulate the reinoculation of microorganisms from upgradient groundwater advecting into the contaminated zone. The other column was fed with sterile groundwater and BTEX to evaluate the regeneration of within-column microorganisms that survived the ethanol exposure. Recovery in both columns was rapid. Unfortunately, during the recovery phase, sterility of the influent groundwater could not be maintained. As a result, recovery by regeneration could not be evaluated. Nonetheless, it is evident that recovery in terms of aerobic BTEX biodegradation was significant under the conditions of the column experiment. Ethanol did not appear to pose a long-term impact on BTEX biodegradation when oxygen and nutrients were in excess. In field situations, nutrients and electron acceptors may be limited; however, ethanol toxicity is not likely to cause a prolonged inhibition of BTEX biodegradation.

The behaviour of hydrocarbon fuels in contaminated groundwater systems is studied using a multicomponent reactive transport model. The simulated processes include residual NAPL dissolution, aerobic and anaerobic biodegradation with daughter-product transport, and transport of a reactive carrier with mixed equilibrium/kinetic sorption. The solution algorithm is based on a three-dimensional Galerkin finite element scheme with deformable brick elements and capacity for a free watertable search. Nonlinearities are handled through Picard iteration. Convergence is rapid for most applications and mass balance errors for all phases are minimal. The model is first applied to simulate a pilot scale diesel fuel dissolution experiment in which humic acid is used as a natural organic carrier to enhance dissolution and to promote biodegradation of the aqueous components. The pilot scale experiment is described by Lesage et al. (1995) and Van Stempvoort et al. (2000). The conceptual model includes 8 unique components dissolving from 500 mL of residual diesel fuel within a 3D saturated domain. Oxygen-limiting competitive aerobic biodegradation with a dynamic microbial population is also included. A mixed 2-site equilibrium/kinetic model for describing sorption of the carrier to the aquifer solids was adopted to reproduce the observed breakthrough of the humic acid and organic components. Most model parameters were obtained independently with minimal calibration. Batch sorption data were found to fit well at the pilot scale, however biodegradation and dissolution rates were not well known and had to be fitted. Simulations confirmed the observed 10-fold increase in effective solubility of trimethylnaphthalene, and increases on the order of 2-5 for methyl- and dimethylnaphthalene. The simulated plumes showed almost complete attenuation after 5 years, in excellent agreement with observed data. A sensitivity analysis showed the importance of carrier concentrations, binding coefficients, dissolution and biodegradation rates. Compared to a dissolution scenario assuming no carrier, the humic acid-enhanced dissolution case decreased the remediation time by a factor of about 5. The second application of the model involves simulating the effect of ethanol on the persistence of benzene in gasoline-impacted groundwater systems. The conceptual model includes a 4-component residual gasoline source which is dissolving at the watertable into a 3D aquifer. Comparisons are made between dissolved plumes from a gasoline spill and those from an otherwise equivalent gasohol spill. Simulations have shown that under some conditions, a 10% ethanol component in gasoline can extend the travel distance of a benzene plume by at least 150% relative to that from an equivalent ethanol-free gasoline spill. The increase is due to preferred consumption of oxygen by ethanol and a corresponding reduction in the biodegradation rate of benzene while the two plumes overlap. Because of differences in retardation however, the ethanol and benzene plumes gradually separate. The impact therefore becomes limited because oxygen rapidly disperses behind the ethanol plume and benzene degradation eventually resumes. A sensitivity analysis for two common spill scenarios showed that background oxygen concentrations, and benzene retardation had the most significant influence on benzene persistence. A continuous gasohol spill over 10 years was found to increase the benzene travel distance by over 120% and a pure ethanol spill into an existing gasoline plume increased benzene travel distance by 150% after 40 years. The results are highly relevant in light of the forthcoming ban of MTBE in California and its likely replacement by ethanol by the end of 2002.

Ethanol can affect the biodegradation of gasoline hydrocarbons in groundwater. High concentrations of ethanol can be toxic to subsurface microorganisms that are otherwise capable of degrading hydrocarbons, such as benzene, toluene, ethylbenzene and xylenes (BTEX). At lower concentrations, ethanol may hinder BTEX degradation through substrate competition and the depletion of inorganic nutrients (e.g., nitrogen and phosphorus), oxygen and other electron acceptors needed for BTEX degradation. A series of laboratory experiments were designed to study the effect of ethanol on aquifer microorganisms and on aerobic BTEX biodegradation. A microcosm experiment was conducted to investigate the effect of ethanol on the biodegradation of BTEX. Microcosms were set up with Borden aquifer material and groundwater in which oxygen and nutrients were not limited. These microcosms contained BTEX in combination with a range of ethanol concentrations. Under these favourable conditions, the presence of ethanol up to concentrations of 1.9% (v/v) (equivalent to 15000 mg/L) caused little inhibition of BTEX degradation. Further experiments were conducted to study the antimicrobial effects of higher concentrations of ethanol. Following exposure to ethanol concentrations of 25% (v/v) or higher, microbial activity and survival was significantly diminished. Results suggest that a high concentration ethanol slug will have a major impact on the microbial community but that there would likely be potential for recovery. The recovery potential was examined further in laboratory column experiments designed to simulate a dynamic field situation where a high ethanol pulse is followed by a BTEX plume. These column experiments were conducted with Borden aquifer material and groundwater under aerobic conditions. The concentration of the ethanol pulse was 25% (v/v), which was expected to significantly alter the microbial population without destroying it. Following the ethanol exposure, groundwater and BTEX were allowed to flow through one column to simulate the reinoculation of microorganisms from upgradient groundwater advecting into the contaminated zone. The other column was fed with sterile groundwater and BTEX to evaluate the regeneration of within-column microorganisms that survived the ethanol exposure. Recovery in both columns was rapid. Unfortunately, during the recovery phase, sterility of the influent groundwater could not be maintained. As a result, recovery by regeneration could not be evaluated. Nonetheless, it is evident that recovery in terms of aerobic BTEX biodegradation was significant under the conditions of the column experiment. Ethanol did not appear to pose a long-term impact on BTEX biodegradation when oxygen and nutrients were in excess. In field situations, nutrients and electron acceptors may be limited; however, ethanol toxicity is not likely to cause a prolonged inhibition of BTEX biodegradation.

Made available in DSpace on 2014-06-11T19:26:46Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-02-27Bitstream added on 2014-06-13T20:15:41Z : No. of bitstreams: 1 moraes_dac_me_botfca.pdf: 849456 bytes, checksum: c3e1db334cc08afff00ab382d3952add (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Universidade Estadual Paulista (UNESP) / O uso inadequado de defensivos agrícolas pode levar a impactos ambientais relevantes, como a contaminação de diversos compartimentos ambientais, sendo os mais vulneráveis, os compartimentos aquáticos. Nesse contexto, a espacialização das estimativas de concentração de defensivos agrícolas na água subterrânea fornece importantes subsídios para a tomada de decisão no gerenciamento e monitoramento do uso de defensivos agrícolas. Assim, este trabalho teve por objetivo espacializar as estimativas de contaminação de águas subterrâneas por defensivos agrícolas, considerando diferentes lâminas de irrigação na Bacia do Rio Pardo, Pardinho-SP. As simulações realizadas com o sistema computacional ARAquá foram realizadas considerando quatro defensivos agrícolas e cinco lâminas de irrigação. Técnicas geoestatísticas foram utilizadas em conjunto com as simulações para obter a espacialização dessas estimativas. Foram obtidos os mapas das estimativas de concentração de defensivos agrícolas na água subterrânea pelo método de interpolação por krigagem, sendo que estes indicaram as áreas com maior potencial de contaminação da água subterrânea. Considerando todas as simulações pode-se concluir que não houve risco de contaminação da água subterrânea por defensivos agrícolas e que as maiores concentrações foram obtidas considerando uma lâmina de irrigação anual de 400 mm. As simulações estimaram que as áreas com maior potencial de contaminação da água subterrânea foram as mais próximas da rede drenagem da Bacia do Rio Pardo. As técnicas de geoestatística contribuíram fortemente para a espacialização das estimativas de concentração de defensivos agrícolas na água subterrânea, por meio da análise dos variogramas e dos mapas gerados pela interpolação por krigagem / Improper use of pesticides can lead to significant environmental impacts such as contamination of environmental compartments, the most vulnerable, the aquatic compartments. In this context, the spatialization of the estimating concentrations of pesticides in groundwater provides important insights for decision making in managing and monitoring of the use of pesticides. Thus, this study aimed to spatialize the estimating of groundwater contamination by pesticides, with different irrigation blades in the Rio Pardo basin, Pardinho-SP. The simulations were performed with the computer system ARAquá considering four pesticides and five irrigation blades. Geostatistical techniques were used in conjunction with the simulations to obtain the spatial distribution of the estimating. The maps of the estimating concentration of pesticides in groundwater were obtained by Kriging interpolation method, and these indicate the areas with greatest potential for groundwater contamination. Considering all the simulations can be concluded that there was no risk of groundwater contamination by pesticides and that the highest concentrations were obtained considering an anual irrigation blade of 400 mm. The simulations have estimated that the areas with greatest potential for groundwater contamination were the closest to the drainage network of the Rio Pardo basin. Geostatistical techniques have contributed greatly to the estimates of spatial concentration of pesticides in ground water, through the analysis of variograms and maps generated by Kriging interpolation

Orientador: Chang Hung Kiang / Banca: Paulo Milton Barbosa Landim / Banca: Didier Gastmans / Banca: Elton Gloeden / Banca: Fernando Krahenbul / Resumo: O gerenciamento de áreas contaminadas objetiva eliminar riscos pela contaminação de água subterrânea em áreas industriais. O comportamento de contaminantes também é controlado pela configuração das litologias, sendo necessária a caracterização geológica para estabelecer um modelo geológico conceitual, subsidiando as ações futuras de investigação e remediação. Em áreas geologicamente complexas, a distribuição das litologias deve ser enfocada, pois, apresenta variação significativa, e o seu conhecimento é de difícil estabelecimento com dados sem qualidade e quantidade. As incertezas associadas à heterogeneidade, tornam mais complexo o conhecimento destas. Neste estudo, foi aplicada investigação em área de Cubatão (SP), geologicamente heterogênea, iniciando pela caracterização regional, estabelecendo o modelo conceitual, a gênese das litologias e simulação numérica de fluxo da água subterrânea para verificação do modelo. Para simulação hipotética de um poço para remediação, foi utilizada simulação estocástica para definição da distribuição litológica, pois, a heterogeneidade pode apresentar diversos cenários para um mesmo conjunto de informações. Estas simulações geraram cenários, utilizados para simulação do poço, obtendo-se distintas zonas de captura. Os efeitos da heterogeneidade mostram que, para projeção de sistema de remediação, devem ser considerados diversos arranjos litológicos, pois, considerando-se modelos simplistas, a remediação será ineficiente, aumentando os custos para novas investigações e ações de remediação adicionais / Abstract: The management of contaminated areas aims to eliminate the risk of groundwater contamination in industrial areas. The behavior of contaminants is controlled by the configuration of lithologies, where geological characterization was needed to establish a conceptual geological model, supporting the actions of future investigation and remediation. In geologically complex areas, the distribution of lithologies should be focused, therefore, the distribution is also complex, and their knowledge is difficult to establish with no data quality and quantity. Uncertainties related to heterogeneity become more complex its definition. In this study, it was applied research in an area located at Cubatão (SP), geologically heterogeneous, starting with the regional characterization, setting the conceptual model, genesis of the lithologies and numerical simulation for model verification. For the simulation of a hypothetical well for remediation, stochastic simulation was used to define the lithological distribution, therefore, the heterogeneity may present different scenarios for a given set of information. These simulations generated scenarios used for simulation of extraction well, resulting in different capture zones. The effects of heterogeneity suggests that for projecting remediation system should be considered different lithological distribution, therefore, considering simplistic models, remediation will be inefficient, increasing costs for new investigations and further remediation actions / Doutor

No description available.

Groundwater related courses are offered through several colleges at Virginia Tech. These classes enroll a diverse group of students with varied academic backgrounds and educational levels. Though these classes emphasize different aspects of groundwater resources, they lack a unified approach in instructional materials and learning methodologies for knowledge they do share. The goals of this research are to lessen the impact of variable student backgrounds and to better integrate the courses to improve teaching and learning, through the development of a multi-tiered, interdisciplinary website, Groundwater Interactive (GWI). GWI, as an educational technology, employs a variety of interactive multimedia. The primary educational components of the website include interactive and graphical models and quizzes, and a student-authored primer. An implementation strategy based on experiential and cooperative learning models is developed for application of the GWI tool in the classroom. An assessment methodology to evaluate the effectiveness of these new learning methods and techniques was also developed, but was not implemented as part of this work. / Master of Science

Groundwater contamination is a very serious problem as it leads to the depletion of water resources. Seawater intrusion is a special category of groundwater contamination that threatens the health and possibly lives of many people living in coastal areas. The focus of this work is to develop a numerical model to study seawater intrusion and its effects on groundwater quality and develop a control method to effectively control seawater intrusion. Two major approaches are used in this study: the first approach is the development of a finite element model to simulate seawater intrusion; the second is the development of a simulation-optimization model to study the control of seawater intrusion in coastal aquifers using different management scenarios. The simulation-optimization model is based on the integration of a genetic algorithm optimization technique with the transient density-dependent finite element model developed in this research. The finite element model considers the coupled flow of air and water and solute transport in saturated and unsaturated soils. The governing differential equations include two mass balance equations of water and air phases and the energy balance equation for heat transfer, together with a balance equation for miscible solute transport. The nonlinear governing differential equations are solved using the finite element method in the space domain and a finite difference scheme in the time domain. A two dimensional finite element model is developed to solve the governing equations and provide values of solute concentration, pore water pressure, pore air pressure and temperature at different points within the region at different times. The mathematical formulation and numerical implementation of the model are presented. The numerical model is validated by application to standard examples from literature followed by application to a number of case studies involving seawater intrusion problems. The results show good agreement with previous results reported in the literature. The model is then used to predict seawater intrusion for a number of real world case studies. The developed model is capable of predicting, with a good accuracy, the intrusion of seawater in coastal aquifers. In the second approach, a simulation-optimization model is developed to study the control of seawater intrusion using three management scenarios: abstraction of brackish water, recharge of fresh water and combination of abstraction and recharge. The objectives of these management scenarios include minimizing the total costs for construction and operation, minimizing salt concentrations in the aquifer and determining the optimal depths, locations and abstraction/recharge rates for the wells. Also, a new methodology is presented to control seawater intrusion in coastal aquifers. In the proposed methodology ADR (abstraction, desalination and recharge), seawater intrusion is controlled by abstracting brackish water, desalinating it using a small scale reverse osmosis plant and recharging to the aquifer. The simulation-optimization model is applied to a number of case studies. The efficiencies of three different scenarios are examined and compared. Results show that all the three scenarios could be effective in controlling seawater intrusion. However, ADR methodology can result in the lowest cost and salt concentration in aquifers and maximum movement of the transition zone towards the sea. The results also show that for the case studies considered in this work, the amount of abstracted and treated water is about three times the amount required for recharge; therefore the remaining treated water can be used directly for different proposes. The application of ADR methodology is shown to be more efficient and more practical, since it is a cost-effective method to control seawater intrusion in coastal aquifers. This technology can be used for sustainable development of water resources in coastal areas where it provides a new source of treated water. The developed method is regard as an effective tool to control seawater intrusion in coastal aquifers and can be applied in areas where there is a risk of seawater intrusion. Finally, the developed FE model is applied to study the effects of likely climate change and sea level rise on seawater intrusion in coastal aquifers. The results show that the developed model is capable of predicting the movement of the transition zone considering the effects of sea level rise and over-abstraction. The results also indicate that the change of water level in the sea side has a significant effect on the position of the transition zone especially if the effect of sea level rise is combined with the effect of increasing abstraction from the aquifer.

Le Site Pilote de Tchernobyl (CPS) est voué à l’étude de la migration des radionucléides à partir de l’une des tranchées creusée pour enfouir la matière contaminée à la suite de l'accident de Tchernobyl (1986). L’objectif de cette thèse est d’étudier les processus de migration des éléments dans la nappe phréatique.D’abord, l’extension maximale du panache de contamination est étudiée à l’aide du traceur conservatif 36Cl. Dans la nappe, les rapports 36Cl/Cl sont 1 à 4 ordres de grandeur supérieurs au rapport naturel théorique (particulièrement en aval de la tranchée), signifiant une importante contamination de la nappe par le 36Cl.Ensuite, un modèle conceptuel des processus géochimiques est proposé à partir de l’étude des variations en [Cl-], [HCO3-], [SO42-], [NO3-], [Na+], [Ca2+], [K+] [Mg2+], [Si], [Fe2+], [Mn2+] et des rapports δ18O et δ2H. Certains éléments sont très influencés par la présence de la tranchée mais des processus naturels peuvent aussi avoir une influence sur géochimie des eaux (eau-roche ou de drainage).Puis, les rapports isotopiques 238U/235U, 86Sr/88Sr et 87Sr/86Sr sont mesurés pour étudier la migration d’U et du Sr. La dissolution des particules de combustible enfouies dans la tranchée et le lessivage des radionucléides qui leur sont associés pourraient avoir un impact significatif sur les rapports isotopiques dans la nappe. Une augmentation des concentrations en [238U] est observée en aval de la tranchée mais les rapports 238U/235U mesurés sont naturels. La procédure d'analyse des rapports 86Sr/88Sr et 87Sr/86Sr ne permet pas d’observer un changement de ces rapports dans la nappe mais une diminution du rapport est observée en profondeur. / The Chernobyl Pilot Site (CPS) was set up to study the migration of radionuclides from one of the trenches dug in situ to bury materials contaminated after Chernobyl accident. The aim of this study is to investigate migration processes in groundwater. At first, the maximal extent of the contaminant plume is investigated based on the study of conservative tracer 36Cl. High contamination of groundwater by 36Cl is shown, with 36Cl/Cl ratios 1 to 4 orders of magnitude higher than the theoretical natural ratio (specifically downgradient of the trench). Then, a conceptual model of the main geochemical processes in groundwater is proposed based on the study of variantions in [Cl-], [HCO3-], [SO42-], [NO3-], [Na+], [Ca2+], [K+] [Mg2+], [Si]), [Fe2+], [Mn2+], and δ18O and δ2H. Some element concentrations are mainly governed by migrations from the trench. However, natural geochemical processes are also assessed to have an influence on groundwater geochemistry (water-rock interaction, leakage). Next, uranium and strontium migrations are investigated based on measurements of 238U/235U, 86Sr/88Sr, 87Sr/86Sr ratios. Indeed, dissolution fuel particles buried in the trench and the release of associated radionuclides is supposed to have a significant impact on those ratios in groundwater. However, in spite of an increase of [238U] concentrations downgradient of the trench, measured 238U/235U ratios in groundwater are in the natural range. Analytical procedure for 86Sr/88Sr and 87Sr/86Sr ratio measurement does not allow observing some trend downgradient of the trench; however, 87Sr/86Sr ratios clearly decrease with the depth.