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.

Supersaturated water injection (SWI) is a novel remediation technology which is able to remove entrapped residual NAPLs from saturated porous media by both volatilization (partitioning of volatile contaminants into the gas phase) and mobilization (displacement of isolated NAPL residuals by gas clusters). The character of gas saturation evolution in-situ in saturated porous media during SWI results in high sweep efficiency. This work focuses on studying the recovery of entrapped residual NAPL by the mobilization mechanism during SWI, thus low-volatility NAPL residuals, kerosene and a kerosene-hexadecane mixture, are used as contaminants. A series of SWI recovery experiments are conducted to investigate the influence of grain size, low-permeability layering, and physical properties of the contaminants on the recovery behavior. For columns contaminated with kerosene, the residual saturation can be reduced to around 4% from an initial value of 16%, and over 70% of the residual kerosene is recovered by a combination of mobilization and volatilization in homogeneous sand packs. For columns contaminated with a kerosene-hexadecane mixture, the final residual saturation is 7.4% and the final NAPL recovery is lower than that in kerosene columns. Grain size has little influence on NAPL recovery, but low permeability layering has a significantly negative influence. Experiments designed to compare SWI to sparging, and water-gas co-injection showed that water-gas co-injection was able to effectively recovery residual NAPLs albeit not as efficiently as SWI, while steady gas sparging is completely ineffective at recovering residual NAPL by mobilization. Based on these experimental observations, a conceptual model, involving double displacements and NAPL bank formation, is purposed to explain the experimental observations.

The possible benefits of thermal remediation of NAPL-contaminated subsurface were analyzed at pore-scale. Force balance analysis was performed to provide the insight and information on the critical conditions for the blob mobilization. First, the critical blob radius for blob mobilization was calculated in terms of blob radius, temperature, and water velocity. Temperature increase enhanced the blob mobilization along with the decrease of interfacial tension. Water velocity increase also enhanced the blob mobilization. Critical water velocity provided the critical condition for the initiation of blob mobilization to distinguish singlet and doublet in blob size. Second, the terminal (or steady state) blob velocity at the steady state blob motion was determined. Increases of temperature and water velocity raised the terminal blob velocity. When the observation of blob mobilization moved from REV scale (macroscale) to pore-scale, terminal blob velocity showed the different phenomena according to the change of oil saturation. At macro-scale, the terminal blob velocity was smaller than water velocity by an order or two. However, the terminal blob velocity reached to water velocity at pore-scale. This investigation would provide the better understanding on the pore-scale analysis of residual NAPL blob mobilization by thermal remediation. Additionally, the pore-scale analysis developed in this study would be incorporated into a general conservation equation in terms of the accumulation of multiple blobs. It would derive continuumaveraged equations that accurately represent pore-level physics. In conclusion, the study on the critical conditions for the initiation of blob mobilization as a single discrete blob would have some contribution to the transport and fate of NAPL contaminant and the desired subsurface remediation.

NAPL (non-aqueous phase liquid) blob mobilization and solubilization models were developed to predict residual NAPL fate and describe flow dynamics of various displacing phases (water and surfactant foam). The models were achieved by pore-scale mass and force balances and were focused on the understanding of the physico-chemical interactions between NAPL blobs and the displacing phases. The pore-level mass balance indicated changes in NAPL saturation instead of mass reduction occurring with blob solubilization. The force balance was used to explain the complex flow configurations among NAPL blobs and the displacing phases. Some factors such as the wettability and the spreading/entering coefficients were useful in determining flow configurations. From the models developed in this study, dimensional analysis was performed to identify NAPL blob motion during water or surfactant foam flooding. In non-dimensionalized forms, a Trapping number employed as an indicator of blob displacement performance was modified to quantify the onset of blob mobilization. Its value for water flooding was nearly 2-3 orders of magnitude greater than that of surfactant foam flooding. Next, to investigate the blob flow regime in porous media, a blob velocity was computed. Regardless of the displacing phases, a blob’s velocity increased with increasing blob sizes after commencement of blob motion, and the velocity of DNAPL (dense non-aqueous phase liquid) blobs was greater than that of LNAPL (light non-aqueous phase liquid) blobs. From this investigation, it is expected that the pore-scale solubilization and mobilization models would provide better understanding leading to a predictive capability for the flow behavior of NAPL blobs removed by various displacing phases in a porous medium. Additionally, the models based on newly approached concepts and modified governing equations would be useful in conceptualization, as well as the model prediction of other immiscible or miscible fluids flowing through a porous medium. Further, the models developed in our study would be a useful contribution to the study of small-scale contaminants or substances such as particle and bacterial transport in porous media.

Minimal research has been conducted to examine dissolution and remediation of NAPL located in lower-permeability (K) media. The purpose of this research was to investigate dissolution of non-uniformly distributed residual NAPL located in lower-K media and how mass transfer was affected. Additionally, in situ chemical oxidation (ISCO) effectiveness using KMnO₄ in the laboratory and field was examined. A series of column and flow cell experiments were conducted with trichloroethene (TCE). For uniformly distributed residual NAPL control experiments, reduced interfacial pool area and resonance time were likely the most important mass transfer limitation. For non-uniformly distributed residual NAPL, by-pass flow attributed to reduced effective permeability was initially the most important factor affecting nonideal mass transfer. Dissolution times increased with physical heterogeneity due to bypass flow. Mass transfer was more non-ideal for non-uniformly distributed NAPL. Nonideal mass transfer was most pronounced for non-uniformly distributed NAPL in lower-K zones. NAPL location influences dissolution behavior and ultimately remediation. Mass flux reduction versus mass reduction comparisons for the experiments exhibited how mass transfer trends vary between systems. The effectiveness of KMnO₄ ISCO of residual TCE located in lower-K media was examined. KMnO₄ solution was flushed through a flow cell followed by water flushing to evaluate long-term mass flux behavior, which was then compared to a water-flush control. For water flushing following KMnO₄ flushing, mass flux was similar to the control experiment. However, since contaminant mass was reduced, the number of pore volumes required for complete TCE removal via water flushing was estimated to be reduced by half. 1,1-Dichloroethene (DCE) is thought to be located in lower permeability strata adjacent to the water table at the Samsonite Building Area. Eight injection wells were emplaced in the source zone area, with well screens spanning the vadose and saturated zones, and injected with ~250 kg of 1.7% KMnO₄ solution. Bench-scale studies using core material determined that DCE was readily degraded by KMnO₄, even at lower reagent concentrations (< 1 mM). The natural oxidant demand was determined to be 1.0 x 10⁻⁵ g of KMnO₄/g of sediment. Aqueous DCE levels dropped below detection after KMnO₄ solution was present.

L’évolution d’une phase microbienne au sein d’un milieu poreux est un processus complexe de par la prise en compte des effets de croissance (ou de mortalité) et d’étalement de la phase cellulaire. D’autres processus tels que l’arrachement d’une partie du biofilm ou l’attachement-détachement de cellules mobiles depuis la phase fluide peuvent aussi contribuer à la variation du volume de biofilm présent. Une meilleure compréhension des interactions mis en jeu entre les processus de croissance de biofilm, du transport de soluté et de l’écoulement et une modélisation rigoureuse de ce processus de croissance à l’échelle microscopique est un enjeu essentiel à une prédiction plus fine du devenir des polluants dans les sols. L’évolution temporelle d’un milieu poreux sous l’effet de l’activité biologique constitue toutefois à l’heure actuelle un défi scientifique majeur d’un point de vue de la modélisation numérique. Les variations locales de la géométrie du domaine (bio-obstruction des pores) induisent en effet une chenalisation de l’écoulement et du transport qui va évoluer au cours du temps. Si différentes méthodes numériques – lagrangiennes ou eulériennes – ont été développées (méthode de capture du front, méthode d’interface diffuse de type « Level Set » ou « Volume Of Fluid »), elles restent souvent peu adaptées à des modélisations 3D à l’échelle du pore (temps de calcul, remaillage parfois nécessaire, problème de gain ou de perte de masse). Nous combinons ici une méthode IBM (Immersed Boundary Method) à une méthode LBM (Lattice Boltzman Method) pour le calcul de l’écoulement en 3D tandis qu’une approche de type VOF (Volume of Fluid) ou par reconstruction d’interface couplée à une discrétisation en Volume Finis est utilisée pour le transport des espèces chimiques. L’intérêt ici de la méthode IB-LBM est de pouvoir bénéficier de la précision de la formulation Lattice- Boltzmann tout en travaillant sur un maillage fixe, un terme correcteur venant modifier la vitesse au voisinage des interfaces mobiles. Le modèle d’écoulement-transport en milieu poreux évolutif développé est ensuite couplé à un modèle d’automate cellulaire prenant en compte les processus d’attachement-détachement. Le modèle est comparé à des benchmarks numériques et utilisé pour étudier les différents régimes de croissance du biofilm en fonction des conditions hydrodynamiques. Dans le dernier chapitre, ce modèle est étendu à la prise en compte d’une phase non-miscible afin d’étudier l’impact des processus de biodégradation sur la dissolution d’une phase polluante piégé. On se limite aux conditions où le NAPL est à saturation résiduelle. L’influence de la production de biosurfactant sur la solubilité du polluant ainsi que la toxicité de celui-ci sur la cinétique de croissance des bactéries est prise en compte. Plusieurs résultats numériques sont présentés afin d’illustrer l’influence des différents paramètres hydrodynamiques sur la dissolution du NAPL. / Mathematical modeling of transport in porous media of organic chemical species in the presence of a bacterial population growing in the form of biofilms is an important area of research for environmental and industrial applications such as the treatment and the remediation of groundwater contaminated by organic pollutants. Biofilms, which are composed of bacteria and extracellular organic substances, grow on the pore-walls of the porous medium. Biodegradable organic solutes are converted into biomass or other organic compounds by the bacterial metabolism. This evolution of the microbial biomass phase within the porous medium is a complex process due mainly to growth (or decay) and spatial spreading of the cellular phase. Processes such as biofilm sloughing and attachment (or detachment) of cells from the fluid phase may also contribute to the biofilm volume variation. In this context, the aim of the thesis is to focus on the mechanisms that control the development of biofilms in porous media and its impact on the hydrodynamic properties of the porous matrix. The objective of this work is to model this pore-scale phenomenon of biofilm growth by integrating the various mechanisms which favor the bacterial development (bacterial proliferation, assimilation of nutrients to synthesize new cellular materials, attachment of cells) or, conversely, which are responsible for slowing down (e.g., detachment of cells, toxicity). An IB-LB model is developed for flow calculation and non-boundary conforming finite volume methods (volume of fluid and reconstruction methods) are used for reactive solute transport. A sophisticated cellular automaton model is developed to describe the spatial distribution of bacteria. Several numerical simulations have been performed on complex porous media and a quantitative diagram representing the transitions between the different biofilm growth patterns was proposed. Finally, the bioenhanced dissolution of NAPL in the presence of biofilms was simulated at the pore scale. The impact of biosurfactants and NAPL toxicity on bacterial growth has been investigated.

Ce manuscrit s'intéresse au devenir de contaminants organiques dans le sol, et plus précisément celui des composés organo-halogénés volatils (COHV).Il propose des outils d'aide à la décision en utilisant la modélisation numérique appliquée à des problématiques environnementales portant sur le traitement de sites et sols pollués par des COHV. Il présente, à ma connaissance, la première modélisation numérique en 3D, grâce au simulateur TMVOC, d'une technique de dépollution physique, à savoir le pompage réussi au sein d'un aquifère d'un liquide en phase non-aqueuse plus dense que l'eau ou Dense Non-Aqueous Phase Liquid (DNAPL). Les très bons résultats de cette simulation permettent d’envisager l’optimisation d’un système de pompage asservi pour dépolluer un site contaminé aux COHV. Cette thèse s'intéresse aussi à une méthode de d'évaluation, à la fois qualitative et quantitative, de l'efficacité du pompage : un test de traçage utilisant des traceurs bisolubles à coefficients de partage variables (partitioning interwell tracer test – PITT). Ce PITT permet de connaître à la fois la répartition spatiale, au sein d’un aquifère, d’une bulle de DNAPL et aussi d’en évaluer sa saturation et donc son volume. Ce manuscrit met à disposition des outils élaborés et adaptés au traitement d'un DNAPL dans un aquifère. La combinaison des deux techniques présentées, à savoir la modélisation d'un pompage de DNAPL et un PITT, sont parfaitement reproductibles dans des environnements similaires et à l'échelle industrielle. Enfin, ces méthodes permettent de réduire considérablement les coûts de caractérisation (PITT) et d'exploitation par l'optimisation de systèmes de pompage / This manuscript deals with the fate of organic contaminants in soil, more precisely of volatile organo-chlorinated compounds (VOHC) and offers some decision making techniques and tools using numerical modelling applied to environmental issues about the treatment of soils contaminated by VOHC. It presents, to the best knowledge of the auhor, the first 3D numerical modelling, with the simulator TMVOC, of a physical treatment technique, namely the successful pumping within an aquifer, of a Dense Non-Aqueous Phase Liquid (DNAPL). The very good results of this simulation give the opportunity to design a controlled and automated pumping system to remediate a polluted site. This thesis also deols with a tracer test assessment method, both qualitative and quantitative, for the efficiency of this pumping : a partitioning interwell tracer test (PITT). The PITT allows us to determine the spatial repartion of the DNAPL and also to assess its saturation, hence its volume. This manuscript offers elaborated tools adapted to the remediation of a DNAPL in an aquifer. The combination of these two techniques, namely the DNAPL pumping and the PITT, are perfectly reproducible in similar environments up to an industrial scale. Finally, exploitation and characterisation costs for DNAPL remediation can be extremely reduced by numerical modelling and optimisation

<p>Chlorinated solvent are volatile organic substances that can be harmful for humans and for the environment. Examples of common chlorinated solvents are perchloroethene, PCE, and trichloroethene, TCE. Chlorinated solvents appear as contaminants in soils primarily where they have been used as washing fluids in dry-cleaning facilities or as degreasers in metal industries. Chlorinated solvents are DNAPLs (dense non-aqueous phase liquids), which means that they are not easily dissolved in water and that they sink to the bottom of the aquifer. Adsorption to soils is low so chlorinated solvents are mobile in soils. Chlorinated solvents can be harmful at low concentrations. Complete degradation can only occur under specific conditions. Because of the properties of these substances, investigation and analysis methodology are extra important for determining transport and risks in a contaminated area.</p><p>In this work, investigation and analysis methods for chlorinated solvents are described. Planning, fieldwork, modeling and risk analysis are described.</p><p>Projects concerning chlorinated solvents completed by Golder Associates AB have been compiled and analysed. Based on the compilation, conclusions have been drawn and statistics have been calculated. Investigations of the relation between concentrations in different media have been made as well as investigations of the relation between degradation products at different distances from the source and at different times after release. The data from the environmental investigations have been compared with theoretical literature values and modelling results.</p><p>The results show that there is a large natural variation in the data and that the differences between different areas are quite large. The results confirm the theory that the percentage of degradation products increases with distance from the source and with time from release. In addition, solvents with a higher degree of chlorination seams to appear to a greater extent in the soil and the more volatile substances seams to appear to a greater extent in the soil air.</p> / <p>Klorerade lösningsmedel är flyktiga klorerade organiska ämnen som kan vara skadliga för människor och miljön. Exempel på vanliga klorerade lösningsmedel är perkloreten, PCE och trikloreten, TCE. Klorerade lösningsmedel förekommer som markföroreningar främst efter användning som tvättvätska i kemtvättar och som avfettningsmedel i metallindustrin. Klorerade lösningsmedel är DNAPLs (dense non-aqueous phase liquids), det innebär att de är svårlösliga i vatten och att de sjunker och lägger sig på botten av akviferen. Fastläggningen i jorden är liten hos klorerade lösningsmedel som därmed är rörliga i marken. De är farliga redan vid små koncentrationer och fullständig nedbrytning sker endast under vissa förutsättningar. Ämnenas egenskaper gör att undersöknings- och analysmetodiken är viktig för att riktigt kunna bestämma deras utbredning och risk på ett förorenat område.</p><p>I detta arbete beskrivs undersöknings- och analysmetodiken för områden förorenade med klorerade lösningsmedel. Upplägg, fältarbete, modellering och riskbedömning beskrivs.</p><p>Projekt som handlar om klorerade lösningsmedel utförda av Golder Associates AB har sammanställts. Sammanställningen har analyserats och utifrån den har olika slutsatser dragits och statistik beräknats. Bland annat har samband mellan halter i olika medier samt samband mellan halter av nedbrytningsprodukter på olika avstånd från källan respektive efter olika lång tid från läckage har undersökts. Data från miljöundersökningarna har även jämförts med teoretiska litteraturvärden samt modelleringsresultat.</p><p>Resultatet visar att den naturliga spridningen av data är stor samt att resultaten skiljer sig åt mellan olika områden. Resultaten bekräftar teorierna att halten nedbrytningsprodukter ökar med avståndet från källan och med tiden samt att ämnen med högre kloreringsgrad finns i större utsträckning i jorden och att flyktigare ämnen finns i större utsträckning i porluften.</p>

In Situ Thermal Treatment (ISTT) is a candidate remediation technology for dense non-aqueous phase liquids (DNAPLs). However, the relationships between gas production, gas flow, and contaminant mass removal during ISTT are not fully understood. A laboratory study was conducted to assess the degree of mass removal, as well as the gas generation rate and the composition of the gas phase as a function of different heating times and initial DNAPL saturations. The temperature of the contaminated soil was measured continuously using a thermocouple to identify periods of heating, co-boiling and boiling. Samples were collected from the aqueous and DNAPL phase of the condensate, as well as from the source soil, at different heating times, and analyzed by gas chromatography/mass spectrometry. In addition to laboratory experiments, a mathematical model was developed to predict the co-boiling temperature and transient composition of the gas phase during heating of a uniform source. Predictions for single-component sources matched the experiments well, with a co-boiling plateau at 88°C ± 1°C for experiments with tetrachloroethene (PCE) and water. A comparison of predicted and observed boiling behaviour showed a discrepancy at the end of the co-boiling period, with earlier temperature increases occurring in the experiments. The results of this study suggest that temperature observations related to the co-boiling period during ISTT applications may not provide a clear indication of complete NAPL mass removal, and that multi-compartment modeling associated with various NAPL saturation zones is required to consider mass-transfer limitations within the heated zone. Predictions for multi-component DNAPL, containing 1,2-Dichloroethane (1,2-DCA), PCE and Chlorobenzene, showed no co-boiling plateau. CB is the least volatile component and dominates in the vapour phase at the end of the co-boiling process, and it can be used as an indicator of the end of the co-boiling stage. Two field NAPL mixtures were simulated using the screening-level analytical model to demonstrate its potential application on ISTT. The two mixtures with similar composition but different mass fractions result in distinct co-boiling temperature and mass transfer behaviour. The non-volatile component in the NAPL mixture results in larger amounts of water consumption and longer ISTT operation time. / Thesis (Master, Civil Engineering) -- Queen's University, 2013-09-30 09:26:00.857

Com a finalidade de estudar o comportamento de fluidos aquosos não miscíveis em água no solo, foram executados ensaios de laboratório, a construção de um modelo físico e a comparação dos dados com a simulação numérica com o programa HSSM. Os ensaios de laboratório tiveram a finalidade de obter os parâmetros do solo utilizado no modelo físico e numérico. Foram obtidas curvas de retenção do solo com concentrações de 2, 5, 10 e 15% de óleo e somente com água, para comparar o comportamento das curvas. Para o modelo físico, foi construído um tanque experimental para simular o derramamento de óleo no solo e, assim, obter uma pluma de contaminação de óleo de maneira controlada. Foram executados três ensaios com o tanque experimental, primeiro com o solo na umidade higroscópica, o segundo com um nível dágua definido, e o terceiro com o solo úmido, mas sem um nível dágua. Destes ensaios no tanque, foram coletadas amostras para a análise em laboratório das concentrações de óleo de cada parte do tanque. A partir dos resultados das curvas características foi possível observar que o óleo influencia principalmente na umidade residual. E a análise das amostras coletadas do tanque experimental indica que a concentração de óleo na pluma estava constante, com concentração de 2% de óleo. Juntando os dados colhidos dos ensaios de laboratório e do tanque experimental, foram executadas simulações da evolução da pluma de contaminação de NAPL para os três casos simulados no tanque experimental. A simulação numérica foi coerente com o modelo físico, mas foi observado que subestima a velocidade de expansão da pluma, principalmente quando o solo está com a umidade baixa. / In order to study the behavior of non-aqueous phased liquids in the soil, laboratory tests were performed, and the construction of a physical model and comparison of data obtained with the numerical simulation with the program HSSM. Laboratory tests are designed to obtain the soil parameters used in the physical and numerical model. Retention curves of soil with concentrations of 2, 5, 10 and 15% of oil and water only were obtained to compare the curves. For the physical model, an experimental tank was built to simulate the oil spill on the ground and have a contamination plume of oil with controlled conditions. Were performed three experiments with the tank, first with the hygroscopic soil moisture, the second with a defined water table, and the third with natural soil moisture, but without a water table. From these tests in the tank, samples were collected for laboratory analysis of concentrations of each part of the oil tank. From the results of the retention curves it was observed that the major oil influence was on residual moisture. And the analysis of samples collected from the experimental tank indicates that the oil concentration in the plume was constant at the concentration of 2% of oil. Combining the data collected in laboratory testing and experimental tank, numerical simulations were performed of the evolution of NAPL contamination plume for the three cases simulated in the experimental tank. The numerical simulation was consistent with the physical model, but it was observed that underestimates the rate of expansion of the contamination plume, especially when the moisture of soil is low.