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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

Fractured rock formations represent a valuable source of groundwater and can be highly susceptible to contamination by dense, non-aqueous phase liquids (DNAPLs). The goal of this research is to evaluate the effectiveness of three accepted remediation technologies for addressing DNAPL contamination in fractured rock environments. The technologies under investigation in this study are chemical oxidation, bioremediation, and surfactant flushing. Numerical simulations were employed to examine the performance of each of these technologies at the field scale. The numerical model DNAPL3D-RX, a finite difference multiphase flow-dissolution-aqueous transport code that incorporates RT3D for multiple species reactions, was modified to simulate fractured rock environments. A gridding routine was developed to allow the model to accurately capture DNAPL migration in fractures and aqueous phase diffusion gradients in the matrix while retaining overall model efficiency. Reaction kinetics code subroutines were developed for each technology so as to ensure the key processes were accounted for in the simulations. The three remedial approaches were systematically evaluated via simulations in two-dimensional domains characterized by heterogeneous orthogonal fracture networks parameterized to be representative of sandstone, granite, and shale. Each simulation included a DNAPL release at the water table, redistribution to pools and residual, followed by 20 years of ‘ageing’ under ambient gradient conditions. Suites of simulations for each technology examined a variety of operational issues including the influence of DNAPL type and remedial fluid injection protocol. Performance metrics included changes in mass flux exiting, mass destruction in the matrix versus the fractures, and percentage of injected remedial fluid interacting with the target contaminant. The effectiveness of the three remediation technologies covered a wide range; the mass of contaminants destroyed were found to range from 15% to 99.5% of the initial mass present. Effectiveness of each technology was found to depend on a variety of critical factors particular to each approach. For example, in-situ chemical oxidation was found to be limited by the organic material present in the matrix of the rocks, while the efficiency of enhanced bioremediation was found to be related to factors such as the location of indigenous bacteria present in the domain and rate of bioremediation. In the chemical oxidation study, the efficiency of oxidant consumption was observed to be poor across the suite of scenarios, with greater than 90% of the injected permanganate consumed by natural oxidant demand. This study further revealed that the same factors that contributed to forward diffusion of contaminants prior to treatment are critical to this remediation method as they can determine the extent of contaminant destruction during the injection period. Bioremediation in fractured rock was demonstrated to produce relatively good results under robust first-order decay rates and active microorganisms throughout the fractures and matrix. It was demonstrated that under ideal conditions, of the total initial mass present, up to 3/4 could be reduced to ethene, indicating bioremediation may be a promising treatment approach due to the effective penetration of electron donor into the matrix during the treatment period and the ongoing treatment that occurs after injection ceases. However, when indigenous bacteria was assumed to exist only within the fractured walls of sandstone, it was found that under the same conditions, the rate of dechlorination was 200 times less than the Base Case. Since the majority of the mass resided in the matrix, lack of bioremediation in the matrix significantly reduced the effectiveness of treatment. Surfactant treatment with Tween-80 was proven to be a relatively effective technique in enhanced solubilisation of DNAPL from the fractures within the domain. However, by comparing the aqueous and sorbed mass at the start and end of the Treatment stage, it is revealed that surfactant treatment is not efficient in removing these masses that reside within the matrix. Furthermore, DNAPLs identified in dead end vertical fractures were found to remain in the domain by the end of the simulations across all scenarios studied; indicating that the injected surfactant experiences difficulty in accessing DNAPLs entrapped in dead end fractures. Altogether, the results underscore the challenge of restoring fractured rock aquifers due to the field scale limitations on sufficient contact between remedial fluids and in situ contaminants in all but the most ideal circumstances.

Groundwater at many existing and former industrial sites and disposal areas is contaminated by halogenated organic compounds that were released into the environment. The chlorinated solvent trichloroethylene (TCE) is one of the most ubiquitous of these compounds. In situ chemical oxidation (ISCO) has been successfully used for the removal of TCE. The objective of this study was to apply the ISCO technology to remediate TCE-contaminated groundwater. In this study, potassium permanganate (KMnO4) was used as the oxidant during the ISCO process. The study consisted bench-scale and pilot-scale experiments. In the laboratory experiments, the major controlling factors included oxidant concentrations, effects of soil oxidant demand (SOD) on oxidation efficiency, and addition of dibasic sodium phosphate on the inhibition of production of manganese dioxide (MnO2). Results show that higher molar ratios of KMnO4 to TCE corresponded with higher TCE oxidation rate under the same initial TCE concentration condition. Moreover, higher TCE concentration corresponded with higher TCE oxidation rate under the same molar ratios of KMnO4 to TCE condition. Results reveal that KMnO4 is a more stable and dispersive oxidant, which is able to disperse into the soil materials and react with organic contaminants effectively. Significant amount of MnO2 production can be effectively inhibited with the addition of Na2HPO4. Results show that the increase in the first-order decay rate was observed when the oxidant concentration was increased, and the half-life was approximately 24.3 to 251 min. However, the opposite situation was observed when the second-order decay rate was used to describe the reaction. Results from the column experiment show that the breakthrough volumes were approximately 50.4 to 5.06 pore volume (PV). Injection of KMnO4 would cause the decrease in TCE concentration through oxidation. Results also indicate that the addition of Na2HPO4 would not inhibit the TCE removal rate. In the second part of this study, a TCE-contaminated site was selected for the conduction of pilot-scale study. A total of eight remediation wells were installed for this pilot-scale study. The initial TCE concentrations of the eight wells were as follows: C1 = 0.59 mg/L, C1-E = 0.64 mg/L, C1-W = 0.61 mg/L, EW-1 = 0.65 mg/L, EW-1E = 0.62 mg/L, EW-1W = 0.57 mg/L, C2 = 0.62 mg/L, C3 = 0.35 mg/L. C1, EW-1, C2, and C3 were located along the groundwater flow direction from the upgradient (C1) to the downgradient location (C3), and the distance between each well was 3 m. C1-E and C1-W were located in lateral to C1 with a distance of 3 m to C1. EW-1E and EW-1W were in lateral to EW-1 with a distance of 3 m to EW-1. In the first test, 2,700 L of KMnO4 solution was injected into each of the three injection wells (C1, C1-E, and C1-W) with concentration of 5,000 mg/L. Three injections were performed with an interval of 6 hr between each injection. After injection, the TCE concentrations in those three wells dropped down to below detection limit (<0.0025 mg/L). However, no significant variations in TCE concentrations were observed in other wells. In the second test, 2,700 L of KMnO4 solution was injected into injection well (EW-1) with concentration of 5,000 mg/L. Six injections were performed with an interval of 6 hr between each injection. After injection, the TCE concentrations in the injection well dropped down to below detection limit (<0.0025 mg/L). TCE concentrations in (C1, C1-E, C1-W, EW-1E, EW-1W, C2, and C3) dropped to 0.35-0.49 mg/L. After injection, no significant temperature and pH variation was observed. However, increase in conductivity and oxidation-reduction potential (ORP) was observed. This indicates that the KMnO4 oxidation process is a potential method for TCE-contaminate site remediation. The groundwater conductivity increased from 500 £gS/cm to 1,000 £gS/cm, and ORP increased from 200 to 600 mv. Increase in KMnO4, MnO2, and total Mn was also observed in wells. Results from the slug tests show that the hydraulic conductivity remained in the range from 10-4 to 10-5 m/sec before and after the KMnO4 injection.

Στόχος της μεταπτυχιακής διατριβής αποτέλεσε η πειραματική μελέτη φαινομένων μεταφοράς μάζας από υγρά μη υδατικής φάσης (NAPLs) σε δισδιάστατα πορώδη δοκίμια. Τα υγρά μη υδατικής φάσης αποτελούνται από υδρογονάνθρακες οι οποίοι διαλύονται μερικώς στο νερό. Αποτελούν τη συχνότερα εμφανιζόμενη πηγή μόλυνσης των υπόγειων υδροφορέων και είναι ιδιαίτερα επιβλαβή για τον άνθρωπο. Ο κύριος διαχωρισμός των NAPLs σε κατηγορίες γίνεται με βάση την πυκνότητά τους σε σύγκριση με αυτή του νερού. Έτσι, υπάρχουν τα Light NAPLs (LNAPLs), τα οποία είναι ελαφρύτερα από το νερό με αποτέλεσμα να επιπλέουν στην επιφάνειά του και τα Dense NAPLs (DNAPLs), τα οποία είναι βαρύτερα από το νερό και διαπερνούν τη μάζα του μέχρι να συναντήσουν κάποιο αδιαπέραστο στρώμα. Η πειραματική διάταξη που χρησιμοποιήθηκε αποτελούνταν από γυάλινα δισδιάστατα πορώδη δοκίμια που είχαν κατασκευαστεί με τη λιθογραφική μέθοδο. Με τη βοήθεια αντλίας τα δοκίμια τροφοδοτούνταν με σταθερή παροχή και σε κατάλληλη χρονική στιγμή γινόταν η εισαγωγή του ρύπου στο δοκίμιο. Στη συνέχεια με τη βοήθεια φωτογραφικής μηχανής λαμβάνονταν στιγμιότυπα σε καθορισμένες χρονικές στιγμές και με γραφικές μεθόδους υπολογιζόταν η μεταφορά μάζας. Στο πρώτο κεφάλαιο, περιέχονται εισαγωγικά στοιχεία για τη δομή και τη φύση των υγρών μη υδατικής φάσης καθώς και οι επιπτώσεις τους στο περιβάλλον. Επίσης, γίνεται μια σύντομη αναφορά στο φαινόμενο της διαχύσεως και στο πρώτο πείραμα που παρατηρήθηκε η διάχυση από τον Dalton και περιγράφεται με συντομία το πείραμα που διεξήχθη. Στο δεύτερο κεφάλαιο, γίνεται εκτενής περιγραφή όλων των στοιχείων των υγρών μη υδατικής φάσης και αναλύεται η κίνηση των υγρών αυτών σε όλα τα είδη εδάφους. Επίσης, εξηγείται η διαφορετική συμπεριφορά που αυτά εμφανίζουν στα διάφορα μέσα με βάση τις φυσικές τους ιδιότητες και επίσης παρουσιάζονται οι πρώτες μαθηματικές σχέσεις που δικαιολογούν την κίνησή τους αυτή. Στο τέλος του κεφαλαίο αναφέρονται και χημικές διεργασίες που συμβαίνουν στο υπέδαφος και επηρεάζουν την κίνηση των NAPLs. Στο τρίτο κεφάλαιο περιγράφεται το φαινόμενο μεταφοράς μάζας στο νερό αλλά και σε πορώδη μέσα. Αναφέρονται και περιγράφονται οι σημαντικότεροι και απαραίτητοι τύποι που περιγράφουν τη μεταφορά μάζας και αναλύονται όλοι οι όροι που παίρνουν μέρος στη σύνταξη των τύπων αυτών. Τέλος, αναφέρονται κάποια πειράματα στα οποία χρησιμοποιήθηκαν οι τύποι που περιέχονται στη θεωρία. Στο τέταρτο κεφάλαιο, περιγράφεται η προετοιμασία της πειραματικής διαδικασίας και αναφέρεται ο τεχνικός εξοπλισμός που χρησιμοποιήθηκε για τη διεξαγωγή της. Περιγράφονται όλα τα στάδια του πειράματος με λεπτομέρειες στις διάφορες μεθόδους που χρησιμοποιήθηκαν για τη κατασκευή και τον υπολογισμό των ιδιότητων των δοκιμίων. Επίσης, γίνεται περιγραφή της λειτουργίας του προγράμματος Comsol που χρησιμοποιήθηκε κατά το σχεδιασμό των δοκιμίων. Στο πέμπτο κεφάλαιο, παρουσιάζονται τα αποτελέσματα της πειραματικής διαδικασίας σε μορφή πινάκων και διαγραμμάτων. Τα αποτελέσματα αναλύονται και περιγράφονται με λεπτομέρεια προβλήματα που προέκυψαν κατά τη διεξαγωγή των πειραμάτων. Τέλος εξάγονται συμπεράσματα και γίνονται υποδείξεις για την περαιτέρω διερεύνηση του φαινομένου. / The aim of this Master thesis was the experimental study of mass transfer phenomena of non-aqueous phase liquids (NAPLs) in two-dimensional porous specimens. The liquid non-aqueous phase consisting of hydrocarbons which partially dissolve in the water. Are the most frequently occurring source of contamination of aquifers and is particularly harmful to humans. The main distinction of NAPLs into categories is based on the density compared to that of water. Thus, there are the Light NAPLs (LNAPLs), which is lighter than water so that float on the surface and Dense NAPLs (DNAPLs), which are heavier than water and penetrate the mass of up to meet a impermeable layer . The experimental setup used consisted of two-dimensional porous glass specimens were manufactured with lithographic method. With the pump cores fed with a constant flow and at an appropriate time was the introduction of the pollutant in the essay. Then with the help of camera footage taken at fixed times and graphical methods estimated the mass transfer. In the first chapter, contained introduction to the structure and nature of the non-aqueous phase liquids and their impact on the environment. Also, there is a brief reference to the effect of diffusion in the first experiment observed the diffusion of the Dalton and briefly describes the experiment conducted. The second chapter is a detailed description of all elements of non-aqueous phase liquids and analyzed the movement of fluids across all kinds of terrain. It also explains the different behavior they show in various media based on physical properties and also presents the first mathematical relationships that justify this movement. At the end of the chapter lists and chemical processes occurring in the soil and affect the movement of NAPLs. The third chapter describes the phenomenon of mass transfer in water and in porous media. Listed and described the most important and necessary formulas describing mass transfer and analyze all terms that take part in the preparation of these types. Finally, some experiments indicated that used types contained in the theory. The fourth chapter describes the preparation of the experimental procedure and specifying the equipment used to conduct it. Describes all stages of the experiment in detail the various methods used to construct and calculate the properties of the samples. Also, there is a description of the operation of the program Comsol used in the design of essays. The fifth chapter presents the results of the experimental procedure in the form of tables and diagrams. The results are analyzed and described in detail problems encountered in conducting the experiments. Finally conclusions are drawn and suggestions are made for further investigation of the phenomenon.

京都大学 / 0048 / 新制・課程博士 / 博士(地球環境学) / 甲第18487号 / 地環博第121号 / 新制||地環||25(附属図書館) / 31365 / 京都大学大学院地球環境学舎環境マネジメント専攻 / (主査)教授 勝見 武, 准教授 田中 周平, 准教授 乾 徹 / 学位規則第4条第1項該当 / Doctor of Global Environmental Studies / Kyoto University / DFAM

Predicting the dissolution rates of immiscible contaminants in groundwater is crucial for developing environmental remediation strategies, but quantitative modeling efforts are inherently subject to multiple uncertainties. These include unknown residual amounts of non-aqueous phase liquids (NAPL) and source zone dimensions, inconsistent historical monitoring of contaminant mass discharge, and the mathematical simulation of field-scale mass transfer processes. Effective methods for simulating NAPL dissolution must therefore be able to assimilate a variety of data through physical and scalable mass transfer parameters to quantify and reduce site-specific uncertainties. This investigation coupled upscaled and numerical mass transfer modeling with uncertainty analyses to understand and develop data-assimilation and parameter-scaling methods for characterizing NAPL source zones and predicting depletion timeframes. Parameters of key interest regulating kinetic NAPL persistence and contaminant fluxes are residual mass and saturation, but neither can be measured directly at field sites. However, monitoring and characterization measurements can constrain source zone dimensions, where NAPL mass is distributed. This work evaluated the worth of source zone delineation and dissolution monitoring for estimating NAPL mass and mass transfer coefficients at multiple scales of spatial resolution. Mass transfer processes in controlled laboratory and field experiments were analyzed by simulating monitored dissolved-phase concentrations through the parameterization of explicit and lumped system properties in volume-averaged (VA) and numerical models of NAPL dissolution, respectively. Both methods were coupled with uncertainty analysis tools to investigate the relationship between data availability and model design for accurately constraining system parameters and predictions. The modeling approaches were also combined for reproducing experimental bulk effluent rates in discretized domains, explicitly parameterizing mass transfer coefficients at multiple grid scales. Research findings linked dissolved-phase monitoring signatures to model estimates of NAPL persistence, supported by source zone delineation data. The accurate characterization of source zone properties and kinetic dissolution rates, governing NAPL longevity, was achieved by adjusting model parameterization complexity to data availability. While multistage effluent rates accurately constrained explicit-process parameters in VA models, spatially-varying lumped-process parameters estimated from late dissolution stages also constrained unbiased predictions of NAPL depletion. Advantages of the numerical method included the simultaneous assimilation of bulk and high-resolution monitoring data for characterizing the distribution of residual NAPL mass and dissolution rates, whereas the VA method predicted source dissipation timeframes from delineation data alone. Additionally, comparative modeling analyses resulted in a methodology for scaling VA mass transfer coefficients to simulate NAPL dissolution and longevity at multiple grid resolutions. This research suggests feasibility in empirical constraining of lumped-process parameters by applying VA concepts to numerical mass transfer and transport models, enabling the assimilation of monitoring and source delineation data to reduce site-specific uncertainties. / Doctor of Philosophy / Predicting the dissolution rates of immiscible contaminants in groundwater is crucial for developing environmental restoration strategies, but quantitative modeling efforts are inherently subject to multiple uncertainties. These include unknown mass and dimensions of contaminant source zones, inconsistent groundwater monitoring, and the mathematical simulation of physical processes controlling dissolution rates at field scales. Effective simulation methods must therefore be able to leverage a variety of data through rate-limiting parameters suitable for quantifying and reducing uncertainties at contaminated sites. This investigation integrated mathematical modeling with uncertainty analyses to understand and develop data-driven approaches for characterizing contaminant source zones and predicting dissolution rates at multiple measurement scales. Parameters of key interest regulating the lifespan of source zones are the distribution and amount of residual contaminant mass, which cannot be measured directly at field sites. However, monitoring and site characterization measurements can constrain source zone dimensions, where contaminant mass is distributed. This work evaluated the worth of source zone delineation and groundwater monitoring for estimating contaminant mass and dissolution rates at multiple measurement scales. Rate-limiting processes in controlled laboratory and field experiments were analyzed by simulating monitored groundwater concentrations through the explicit and lumped representation of system properties in volume-averaged (VA) and numerical models of contaminant dissolution, respectively. Both methods were coupled with uncertainty analysis tools to investigate the relationship between data availability and model design for accurately constraining system parameters and predictions. The approaches were also combined for predicting average contaminant concentrations at multiple scales of spatial resolution. Research findings linked groundwater monitoring profiles to model estimates of contaminant persistence, supported by source zone delineation data. The accurate characterization of source zone properties and contaminant dissolution rates was achieved by adjusting model complexity to data availability. While monitoring profiles indicating multi-rate contaminant dissolution accurately constrained explicit-process parameters in VA models, spatially-varying lumped parameters estimated from late dissolution stages also constrained unbiased predictions of source mass depletion. Advantages of the numerical method included the simultaneous utilization of average and spatially-detailed monitoring data for characterizing the distribution of contaminant mass and dissolution rates, whereas the VA method predicted source longevity timeframes from delineation data alone. Additionally, comparative modeling analyses resulted in a methodology for scaling estimable VA parameters to predict contaminant dissolution rates at multiple scales of spatial resolution. This research suggests feasibility in empirical constraining of lumped parameters by applying VA concepts to numerical models, enabling a comprehensive data-driven methodology to quantify environmental risk and support groundwater cleanup designs.

One of the most significant challenges faced when modeling mass transfer from contaminant source zones is uncertainty regarding parameter estimates. These rate parameters are of particular importance because they control the connectivity between a simulated contaminant source zone and the aqueous phase. Where direct observation has fallen short, this study attempts to interpret field data using an inverse modeling technique for the purpose of constraining mass transfer processes which are poorly understood at the field scale. Inverse modeling was applied to evaluate parameters in rate-limited models for mass transfer. Two processes were analyzed: (i) desorption of hydrophobic contaminants and (ii) multicomponent Non-Aqueous Phase Liquid (NAPL) dissolution. Desorption was investigated using data obtained from elution experiments conducted with weathered sediment contaminated with 2,4,6 trinitrotoluene (TNT) (Sellm and Iskandar, 1994). Transport modeling was performed with four alternative source models, but predictive error was minimized by two first-order models which represented sorption/desorption using a Freundlich isotherm. The results suggest that first-order/Freundlich models can reproduce dynamic desorption attributed to high-and-low relative energy sorption sites. However, additional experimentation with the inversion method suggests that mass constraints are required in order to appropriately determine mass transfer coefficients and sorption parameters. The final portion of this research focused on rate-limited mass transfer from multicomponent NAPLs to the aqueous phase. Previous work has been limited to bench and intermediate scale findings which have been shown to inadequately translate to field conditions. Two studies were conducted in which numerical modeling was used to reproduce dissolution from multicomponent NAPL sources. In the first study, a model was generated to reproduce dissolution of chloroform (TCM), trichloroethylene (TCE) and tetrachloroethylene (PCE) observed during an emplaced-source field experiment conducted within a flow cell (Broholm et al., 1999). In the second study, a methodology was developed for analyzing benzene, toluene, ethylbenzene and xylene (BTEX) data during a field-scale mass transfer test conducted within a vertically-smeared source zone (Kavanaugh, 2010). The findings suggest that the inversion technique, when provided appropriate characterization of site and source parameters and when given appropriate dataset resolution, represents a viable method for parameter determination. Furthermore, the findings of this research suggest that inversion-based modeling provides an innovative predictive method for determining mass transfer parameters for multicomponent mixtures at the field scale. / Ph. D.

[Truncated abstract] To date, many subsurface contaminant modelling studies have focused on increasing model complexity and measurement requirements to improve model accuracy and widen model application. However, due to the highly complex and heterogeneous nature of flow in the subsurface, the greater benefit in model development may lie in decreasing complexity by identifying key processes and parameters, simplifying the relationships that exist between them, and incorporating these relationships into simple models that recognise or quantify the inherent complexity and uncertainty. To address this need, this study aims to identify and isolate the key processes and parameters that control dense nonaqueous phase liquid (DNAPL) and aqueous phase migration through single, onedimensional fractures. This is a theoretical representation which allows the study of processes through conceptual and mathematical models. Fracture systems typically consist of multiple two-dimensional fractures in a three-dimensional network; however, these systems are computationally and conceptually demanding to investigate and were outside of the scope of this study. This work initially focuses on DNAPL migration in single, one-dimensional fractures. The similitude techniques of dimensional and inspectional analysis are performed to simplify the system and to develop breakthrough time scale factors. This approach relies heavily on the limitations of the equation used for the analysis and on the difficulty in representing variable aperture scenarios. The complexity of the conceptual model is then increased by embedding the fracture in a two-dimensional, porous matrix. ... These tools can be readily applied by the field investigator or computer modeller to make order-of-magnitude estimates of breakthrough times, reduce or target measurement requirements, and lessen the need to employ numerical multiphase flow models. To determine the implications of the results found in the one-dimensional studies to applications at the field scale, the complexity of the conceptual model was increased to a single, two-dimensional, planar fracture embedded in a three-dimensional porous matrix. The focus of this study was not DNAPL breakthrough times but the relative importance and interaction of different mass transport processes and parameters on plume migration and evolution. Observations clearly show that estimates of the size, location and concentration of the plume is highly dependent on the geologic media, the temporal and spatial location and resolution of measurements, and on the history, mass and location of the DNAPL source. In addition, the processes controlling mass transport (especially matrix diffusion and back diffusion) act in combination at the field scale in ways not always expected from an analysis of processes acting individually at smaller spatial and temporal scales. Serious concerns over the application of the common '1% Rule of Thumb' to predict DNAPL presence and the use of remediation efforts that rely largely on natural attenuation are raised. These findings have major implications for the field worker and computer modeller, and any characterisation, monitoring or remediation program development needs to be sensitive to these findings.

Environmental pollution has become a global concern as consequence of industrializa-tion and urbanization. The ongoing subsurface contamination by dense non-aqueous phase liquids (DNAPLs) bears tremendous hazardous potential for humans and ecosys-tems including aquifer systems. Intended or accidental spill events have led to a vast number of registered sites affected by DNAPL type chemicals. Despite the existence of novel techniques for their exploration, characterization and remediation, economical constraints often limit efforts for risk prevention or reduction, so that information and data to characterize highly complex DNAPL contamination scenarios are often insuffi-cient and compensated by natural attenuation of groundwater-dissolved contaminant plumes. Especially, knowledge on the DNAPL source zone geometry (SZG) and source zone formation are critically required yet very scarce. Against the previously stated background, this cumulative doctoral dissertation critically examined the processes of DNAPL source zone formation at laboratory scale. A comprehensive literature review identified current limitations and open research questions in the latter research field, revealing evidence for the relevance of SZG for plume response at different scales. Giv-en only a limited number of published studies related to DNAPL source zone formation, two simplified experimental setups mimicking source zone formation in an initially fully water-saturated aquifer were developed and intensively tested. The performance of aqueous and non-wetting phase dyes was evaluated for DNAPL release into three non-consolidated porous media using reflective optical imaging in combination with a cus-tom-made image processing and analysis (IPA) framework. The latter suite allowed for the generation of physically plausible DNAPL saturation distributions with determinable level of uncertainty. Then, a limited number of DNAPL release experiments were per-formed under controlled ambient as well as with boundary and initial conditions to generate robust observation data, while further adopting the IPA framework. The latter data was introduced into a numerical multiphase flow model. While most system pa-rameters could be directly determined, the parameters defining the capillary pressure-saturation and relative permeability-saturation retention curves were inversely deline-ated through a classical Monte Carlo analysis. Overall, the successfully calibrated nu-merical setup mimicking the transient DNAPL source zone formation allowed to quanti-fy uncertainties related to the experiment, IPA framework and model setup configura-tion. In addition, a number of new research questions pointing towards future im-provements of laboratory-scale methodologies to understand DNAPL contamination were derived. Especially in light of numerous existing contaminated sites with unclear history and even more vague future, given by potential impacts through climate change and anthropogenic activity, an increasing need for sophisticated strategies to better un-derstand DNAPL contamination and to reduce hazard potential is expected.:Statement I List of publications II Abstract VI Acknowledgements and funding information IX List of figures XIII List of tables XIV Abbreviations and symbols used in the main text XV 1 Introduction and background 1-1 1.1 Motivation of this thesis 1-1 1.2 Incorporation of this thesis in research projects 1-4 1.3 Definition of objectives and workflow strategy of this thesis 1-5 1.4 Formal structure of this thesis 1-11 2 Existing knowledge on DNAPL contamination 2-1 3 Fundamentals of DNAPL migration in porous media 3-1 3.1 Basic concepts for multiphase flow in porous media 3-1 3.2 Capillary pressure-saturation correlation 3-3 3.3 Relative permeability-saturation correlation 3-5 3.4 Balance equations for laminar fluid phase flow in porous media 3-7 4 Core research complex A : Development of a framework for the semi-automatized generation of DNAPL saturation distribution observation data 4-1 5 Core research complex B : Experimental and model-based simulation of DNAPL source zone formation 5-1 6 Summary and conclusions 6-1 6.1 Summary of perceptions for each main section of this thesis 6-1 6.2 New research questions with regard to DNAPL source zone formation at the laboratory scale 6-5 6.3 General recommendations for future works related to DNAPL contamination 6-8 References Ref-1 Appendix I : ENGELMANN ET AL. (2019a) App I-1 Published journal article App I-1 Appendix II : ENGELMANN ET AL. (2019b) App II-1 Published journal article App II-1 Electronic Supplementary Material 1 : Unprocessed raw TIFF format images used for IPA frame-work evaluation App II-26 Electronic Supplementary Material 2 : Sensitivities for color model change and binary conversion algorithms App II-36 Electronic Supplementary Material 3 :Relevance of spatially non-uniform illumination correction and background exclusion App II-76 Appendix III : ENGELMANN ET AL. (2021) App III-1 Published journal article App III-1 Electronic Supplementary Material 1 : Unprocessed raw TIFF format images for IPA framework ap-plication App III-30 Electronic Supplementary Material 2 : Processed images with all intermediate steps of IPA frame-work application App III-58 Electronic Supplementary Material 3 : IPA fitness App III-86 Electronic Supplementary Material 4 : Partial objective functions App III-87 Electronic Supplementary Material 5 : Model verification App III-93