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Laboratory and Modelling Study Evaluating Thermal Remediation of Tetrachloroethene and Multi- Component Napl Impacted Soil

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LABORATORY AND MODELLING STUDY EVALUATING THERMAL REMEDIATION OF TETRACHLOROETHENE AND MULTI- COMPONENT NAPL IMPACTED SOIL by Chen Zhao A thesis submitted to the Department of Civil Engineering In conformity with the requirements for Master of Applied Science Queen’s University Kingston, Ontario, Canada (September 2013) Copyright © Chen Zhao, 2013 Abstract Dense non-aqueous phase liquids (DNAPLs) such as chlorinated solvents, coal tar and creosote are some of the most problematic groundwater and soil contaminants in industrialized countries throughout the world. In Situ Thermal Treatment (ISTT) is a candidate remediation technology for this class of contaminants. 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. Experiments consisted of a soil, water, and DNAPL mixture packed in a 1 L jar that was heated in an oven. Gas produced during each experiment, which consisted of steam and volatile organic compounds (VOCs), was collected and condensed to quantify the gas generation rate. The temperature of the contaminated soil was measured continuously using a thermocouple embedded in the source zone, and was used 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 ii 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. 1,2-DCA, the most volatile component, was found to be removed from soil by heating fastest during co-boiling. 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, which have 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. iii Acknowledgements This research project was supported by student scholarships from Queen’s University and the Natural Sciences and Engineering Research Council (NSERC) of Canada through a Strategic Project Grant. I would like to express my appreciation to my supervisors Dr. Kevin Mumford and Dr. Bernie Kueper. You provided me the opportunity to work on this project, which makes my knowledge and experience extended. Your guidance, advice and encouragement have helped me a lot to complete my thesis research. Grateful thanks to the technical support provided by Stan Prunster and Neil Porter. The assistance of Dr. Allison Rutter and with Paula Whitley at the Queen’s University Analytical Services Unit was essential for development of the analytical method. Many thanks to the members of the groundwater research group, especially Eric Martin, Paul Hegele, Sean Bryck and Owen Miles for their support and help. I also would like to express my appreciation to my parents for their endless love, support and encouragement. iv Forward This thesis has been written in a manuscript format. Chapter 1 gives a general introduction, and Chapter 2 provides a review of relevant literature. Chapters 3 and 4 are independent manuscripts that will be submitted for publication. I will be the first author on both of these publications; Drs. Mumford and Kueper will be coauthors. Chapter 5 summarizes the experimental and modeling results of this study, and also gives recommendations of future study. Supplemental experimental data and calculations, information on the analytical method and analytical error, details regarding the mathematical model, information on the properties of 1,2-dichoroethane, tetrachloroethene and chlorobenzene as a function of temperature, and the soil moisture measurements by time domain reflectometry (TDR) are provided in Appendices A through E. v Table of Contents Abstract ........................................................................................................................................... ii Acknowledgements ........................................................................................................................ iv Forward ............................................................................................................................................v List of Figures ................................................................................................................................ ix List of Tables ................................................................................................................................. xi Nomenclature ................................................................................................................................ xii Abbreviations ............................................................................................................................... xvi Chapter 1 Introduction ......................................................................................................................................1 1.1 DNAPL and Chlorinated Solvents ..........................................................................................1 1.2 Thermal Remediation ..............................................................................................................3 1.3 Research Objectives ................................................................................................................4 1.4 Thesis Overview .....................................................................................................................5 1.5 Literature Cited .......................................................................................................................7 Chapter 2 Literature Review .............................................................................................................................8 2.1 Heat Transfer Mechanisms .....................................................................................................8 2.1.1 Conduction Overview .................................................................................................8 2.1.2 Conduction in Porous Media ....................................................................................10 2.1.3 Convection Overview ...............................................................................................12 2.1.4 Convection in Porous Media ....................................................................................13 2.1.5 Thermal Properties of Soil ........................................................................................13 2.2 Phase Change ........................................................................................................................14 2.2.1 Boiling of Pure Liquids ............................................................................................14 2.2.2 Boiling of Miscible Mixtures ...................................................................................17 2.2.3 Boiling of Immiscible Mixtures ...............................................................................18 2.3 Effects of Temperature on Physicochemical Properties .......................................................22 2.3.1 Water-Gas Partitioning (Henry’s Law) ....................................................................22 2.3.2 DNAPL-Water Partitioning (Solubility) ..................................................................23 2.3.3 Adsorption ................................................................................................................24 vi 2.3.4 Total VOC Concentration .........................................................................................25 2.4 ISTT Technologies ................................................................................................................26 2.4.1 Electrical Resistance Heating ...................................................................................26 2.4.2 Thermal Conductive Heating ...................................................................................28 2.4.3 Importance of Vapour Extraction .............................................................................29
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