The magnitude of contaminant mass flux reduction associated with a specific amount of contaminant mass removed is a key consideration for evaluating the effectiveness of a source-zone remediation effort. Thus, there is great interest in characterizing, estimating and predicting relationships between mass flux reduction and mass removal. Intermediate-scale flow- cell experiments and published data for several field studies were examined to evaluate factors controlling the mass-flux-reduction/mass-removal relationship. Flow-cell experiments evaluated the impact of source-zone architecture and flow-field heterogeneity on mass-flux-reduction/mass-removal behavior. Significant reductions in mass flux occurred for systems wherein immiscible-liquid mass was present at both residual saturation and in high saturation pools. For a system with immiscible liquid present in multiple zones of different permeability, an increase in mass flux was observed for late stages of mass removal. Image analysis confirmed that the late stage increase in mass flux was attributed to changes in relative permeability. Early reductions in mass flux were also observed for systems wherein immiscible-liquid mass was poorly accessible to flowing water. End-point analysis, based on comparing masses and mass fluxes measured before and after a source-zone remediation effort, conducted for 21 field remediation projects ranged from slightly less than to slightly greater than one-to-one. Time-continuous analysis, based on continuous monitoring of mass removal and mass flux, performed for two sites illustrated the dependence of the mass-flux-reduction/mass-removal relationship on source-zone architecture and mass-transfer processes. Minimal mass flux reduction was observed for a system wherein mass removal was relatively efficient. Conversely, a significant degree of mass flux reduction was observed for a site wherein mass removal was inefficient. A simple mass-removal function was used to evaluate the measured data at both the intermediate and field scales. This function was unable to capture the complex behavior observed for some of the systems unless specific measurable system parameters were incorporated into the function. Finally, mathematical models of varying complexity used to simulate immiscible liquid dissolution illustrated the dependence of the calibrated dissolution rate coefficient on implicit and explicit consideration of larger-scale factors influencing immiscible liquid dissolution.

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abstract: This work focuses on a generalized assessment of source zone natural attenuation (SZNA) at chlorinated aliphatic hydrocarbon (CAH) impacted sites. Given the numbers of sites and technical challenges for cleanup there is a need for a SZNA method at CAH impacted sites. The method anticipates that decision makers will be interested in the following questions: 1-Is SZNA occurring and what processes contribute? 2-What are the current SZNA rates? 3-What are the longer-term implications? The approach is macroscopic and uses multiple lines-of-evidence. An in-depth application of the generalized non-site specific method over multiple site events, with sampling refinement approaches applied for improving SZNA estimates, at three CAH impacted sites is presented with a focus on discharge rates for four events over approximately three years (Site 1:2.9, 8.4, 4.9, 2.8kg/yr as PCE, Site 2:1.6, 2.2, 1.7, 1.1kg/y as PCE, Site 3:570, 590, 250, 240kg/y as TCE). When applying the generalized CAH-SZNA method, it is likely that different practitioners will not sample a site similarly, especially regarding sampling density on a groundwater transect. Calculation of SZNA rates is affected by contaminant spatial variability with reference to transect sampling intervals and density with variations in either resulting in different mass discharge estimates. The effects on discharge estimates from varied sampling densities and spacings were examined to develop heuristic sampling guidelines with practical site sampling densities; the guidelines aim to reduce the variability in discharge estimates due to different sampling approaches and to improve confidence in SZNA rates allowing decision-makers to place the rates in perspective and determine a course of action based on remedial goals. Finally bench scale testing was used to address longer term questions; specifically the nature and extent of source architecture. A rapid in-situ disturbance method was developed using a bench-scale apparatus. The approach allows for rapid identification of the presence of DNAPL using several common pilot scale technologies (ISCO, air-sparging, water-injection) and can identify relevant source architectural features (ganglia, pools, dissolved source). Understanding of source architecture and identification of DNAPL containing regions greatly enhances site conceptualization models, improving estimated time frames for SZNA, and possibly improving design of remedial systems. / Dissertation/Thesis / Ph.D. Civil and Environmental Engineering 2013

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.

Verunreinigtes Grundwasser stellt eine ernsthafte Bedrohung für die Trinkwasser-Ressourcen auf der ganzen Welt dar. Verunreinigte Grundwasser können zwar in Brunnen detektiert werden, eine ordnungsgemäße Sanierung ist jedoch häufig nur erfolgreich, wenn die Quelle der Verunreinigung erfasst und entfernt wird. Wenn von Anbeginn eines Sanierungsprojektes ein Schwerpunkt auf die Erkennung und Eingrenzung des Verunreinigungsherdes gelegt wird, kann die Sanierung direkt an dieser Stelle ansetzen und zudem hohe Grundwasser-Sanierungskosten verringert werden. ModBack ist eine Software, die mehrere bestehende Modellierungs-Werkzeuge in einer, ein-fach zu verwendenden, ESRI ArcGIS 10-basierten Schnittstelle vereinigt und hilft mögliche Schadstoffquelle Zonen im Untergrund abzugrenzen. Diese Software ist in Visual Basic 3.5 geschrieben und verwendet ArcObjects Bibliotheken, um die erforderlichen GIS-Anwendungen zu implementieren. Es kann ohne Änderung auf allen Microsoft Windows-basierten PC‘s mit ausreichend RAM und mindestens Microsoft. NET Framework 3.5 verwendet werden. Die Nutzung von ModBack erfordert zusätzliche Installation der folgenden Software: Processing Modflow Pro 7.0 (PMWin), MODPATH, CSTREAM (Bayer-Raich et al., 2003a, Bayer-Raich et al., 2003b, Bayer-Raich et al., 2004), Golden Software Surfer, Microsoft Excel und NAS (eine Software zur Berechnung des natürlichen Schadstoffabbaus). Die grafische Benutzeroberfläche (GUI) von ModBack ist in vier Verfahrensschritte Dateneingabe, Grundwassermodellierung, Partikel Backtracking und Analysen getrennt. Geographischen Eingangsdaten werden für eine geografische Übersicht des Testfeldes benötigt. Sie bestehen meist aus georeferenzierten Informationen des Testfeldes und Informationen zur unterirdischen Grundwasserverunreinigungen. Grundwasseranalysen werden entweder durch konventionelle Probennahme aus Grundwassermessstellen oder durch die Durchführung integraler Pumpversuche an Kontrolleben mit eine bestimmten Konzentration/Zeit- Serie (CT-series) gesammelt. Aus den Pumpversuchen resultierende hydraulische Daten werden zusammen mit allen anderen verfügbaren Informationen zur Erstellung eines grundlegenden Grundwasserströmungsmodells des Testfeldes verwendet. Nachfolgende Backtracking Verfahren, als auch die Berechnung von advektivem Schadstofftransport beziehen sich auf die-ses Strömungsfeld und werden entlang einer zuvor definierten Kontrollebene berechnet. Eine Analyse der Backtracking-Ergebnisse erfolgt innerhalb ModBack. Die potenzielle Quelle von Kontaminationen oder deren Abwesenheit werden basierend auf dem Verfahren nach Jarsjö et al. (2005) bestimmt. Die Länge einer Schadstofffahne kann anhand von Fahnenlängen Statistiken und /oder dem Abbau erster Ordnung Abbau Gleichungen oder Berechnungen auf ortsspezifische hydraulischen und chemischen Parametern beruhen. Ferner ist ein analytisches Instrument enthalten, um die Verteilung der Verunreinigungen über eine Steuerebene zu identifizieren. Alle relevanten Ergebnisse können als Vektordaten in ModBack graphisch dargestellt und gespeichert werden und sind somit kompatibel mit weiteren GIS-Software Produkten. ModBack wurde bereits an Testgebieten in Slowenien und Süddeutschland angewendet, um die möglichen Zonen der Verunreinigungsquelle oder deren Abwesenheit zu begrenzen. Auf dem Testgelände in Süddeutschland sind diese Abgrenzungen vergleichbar mit früheren Untersuchungen vor Ort und unterstützt somit die Funktionalität der Software ModBack. Mit ModBack, steht ein Werkzeug zur Verfügung, die bereits jetzt Um-welt-Beratern, Ingenieuren und Umwelt-Agenturen ermöglicht denkbare Quellen der Verunreinigung bei der Planung der Untersuchungen vor Ort und Sanierungsmaßnahmen abzugrenzen, und hilft Kosten deutlich zu senken.

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