The efficacy of injection-driven remediation techniques for non-aqueous phase liquid (NAPL) source zones is limited by the principle that fluid flow is focused along paths of least hydraulic resistance. The pressure pulse technology stands among a number of innovative methods that have been developed with the aim of overcoming or mitigating this limitation. The objective of this research was to observe and document differences in saturated groundwater flow and solute transport between an injection using a conventional or continuous pressure delivery approach and an injection using a pressure pulsing instrument. The underlying motivation was to identify engineering opportunities presented by pressure pulsing with the potential to improve remediation efficiency at contaminated sites. A series of tracer injections were conducted in the unconfined aquifer at the University of Waterloo Groundwater Research Facility at Canadian Forces Base (CFB) Borden near Alliston, ON (homogeneous fine sand), and in the shallow aquifer at a groundwater research site located on the North Campus at the University of Waterloo (moderately heterogeneous with discrete layers varying from fine sand to silt). A single injection well was used at each site for both the conventional and pressure pulsing injections. Different tracers were used for consecutive injections. Bromide, Lithium, Chloride, and fluorescent dyes (Rhodamine WT and Sulforhodamine B) were used. Formation pressurization data was captured by pressure transducers. The spatial distribution of the injected tracers was monitored at a series of multilevel wells. A groundwater flow and solute transport modeling exercise (MODFLOW and MT3DMS numerical engines) simulating the rapid boundary pressure modulation that occurs in association with pressure pulsing was conducted to complement the field injections. A two-dimensional domain was used to conduct a parametric investigation of pressure modulation and its effect on flow and transport. A three-dimensional domain served to scale-up the two-dimensional results and for benchmarking against field observations. Pressure pulsing simulation results reveal that repeated sudden onset of injection cessation produces brief periods of gradient reversal near the injection well and the development of a mixing zone around the injection well. The spatial extents of this mixing zone are highly dependent upon the hydraulic diffusivity of the medium. Greater heterogeneity in combination with presence of high hydraulic diffusivity pathways maximized the extent of the mixing zone and the magnitude of transverse and reversal hydraulic gradients. Lower pulsing frequency and higher pulsing amplitude favoured a more significant mixing zone, though these effects were secondary to geologic properties. Use of the pressure pulsing tool did not manifest into distinct changes in tracer breakthrough at either field research site. Comparison between tracer tests was complicated by sorption of fluorescent dyes and ongoing well development. Solute transport simulation results demonstrated augmentation of dispersion arising from the mixing zone phenomenon, but no distinct changes in advection.

The feasibility of applying a recently developed liquid-liquid extraction method termed Predispersed Solvent Extraction (PDSE) in an <i>ex situ</i> pump-and-treat system to remove trace amounts of dissolved chlorinated solvents like perchloroethylene (PCE) and trichloroethylene (TCE) from contaminated ground water has been investigated. In PDSE, the solvent is comminuted into globules with diameters ranging from submicron to 100 microns, and stabilized by a surfactant film prior to contact with the aqueous feed. These stabilized globules, termed oil-core aphrons (OCAs), disperse readily in water since water is the continuous phase in systems where the oil-water phase ratios can be as high as 9. Due to their fine particle size and large surface area, high extraction mass-transfer rates are achieved with minimal mixing. OCA phase separation from water can be expedited with microbubble foam flotation. Experiments in this investigation focused on PDSE process development for this groundwater remediation application. Distribution coefficients for PCE and TCE in possible OCA solvents were determined experimentally and agree with published calculated values. Various surfactant/solvent OCA formulations using the aforementioned solvents were examined with emphasis on creating a weakly stable dispersion which would maximize extraction efficiency yet destabilize sufficiently to permit rapid flotation with minimum losses in the raffinate. Accelerating phase separation, hence solvent recovery, through dispersion chemical destabilization with salts, coagulants, and flocculants at varied pH was examined with and without microbubble flotation. The presence of OCAs in the aqueous phase reduced vapor phase concentrations of PCE as much as 96% and was assessed through apparent Henry's Law constants. TCE concentrated in dodecane OCA extract was degraded with a CO-dehydrogenase enzyme complex to cis 1,2-dichloroethylene, trans 1,2-dichloroethylene, and 1,1-dichloroethylene, and vinyl chloride as a possible means of destroying TCE dissolved in the extract. Based on the implications of these experiments, the development of a PDSE <i>ex situ</i> pump-and-treat system appears technically feasible and a conceptual process layout has been provided. / Master of Science

In situ thermal treatment (ISTT) applications require successful gas capture for the effective remediation of chlorinated solvent dense non-aqueous phase liquid (DNAPL) source zones. Gas production and transport mechanisms during bench-scale electrical resistance heating (ERH) experiments were examined in this study using a quantitative light transmission visualization method. Processed images during water boiling indicated that gas bubble nucleation, growth and coalescence into a connected steam phase occurred at critical gas saturations of Sgc = 0.233 ± 0.017, which allowed for continuous gas transport out of the heated zone. Critical gas saturations were lower than air-water emergence gas saturations of Sgm = 0.285 ± 0.025, derived from the inflection point of ambient temperature capillary pressure-saturation curves. Coupled electrical current and temperature measurements were identified as a metric to assess gas phase development. Processed images during co-boiling of pooled trichloroethene (TCE) DNAPL and water indicated that discontinuous gas transport occurred above the DNAPL pool. When colder zones were introduced, condensation prevented the development of continuous steam channels and caused redistribution of DNAPL along the vapour front. These results suggest that water boiling temperatures should be targeted throughout the subsurface (i.e., from specific locations of DNAPL to extraction points) during ERH applications. Because convective heat loss and non-uniform power distributions have the potential to prevent the achievement of boiling temperatures, a thermal enhancement was developed where dissolved gas delivered to the target heated zone liberates from solution at elevated temperatures and increases gas production. Processed images of ERH-activated carbon dioxide (CO2) exsolution indicated that discontinuous gas transport occurred above saturations of Sg = 0.070 ± 0.022. Maximum exsolved gas saturations of Sg = 0.118 ± 0.005 were sustained during continuous injection of the saturated CO2 solution into the heated zone. Estimated groundwater relative permeabilities of krw = 0.642 ± 0.009 at these saturations are expected to decrease convective heat loss. Discontinuous transport of exsolved gas at sub-boiling temperatures also demonstrated the potential of the enhancement to bridge vertical gas transport through colder zones. In conclusion, sustained gas saturations and transport mechanisms were dependent on the mechanism of gas production and effects of condensation. / Thesis (Master, Civil Engineering) -- Queen's University, 2014-03-27 15:26:30.683

La dépollution des eaux souterraines est actuellement une des principaux défis environnementaux, considérant le nombre de sites contaminés et le risque posé à la santé humaine et à l'environnement par l'exposition à la contamination des eaux souterraines. La barrière réactive perméable (PRB) est une technologie in situ passive pour la remédiation des eaux souterraines contaminées. Il se compose d'une barrière placée perpendiculairement à l'écoulement des contaminants et constituée d'un matériau réactif qui traite la panache de contaminants le traversant sous le gradient hydraulique naturel. C’est la technologie de remédiation des eaux souterraines la plus rentable ; elle permet l'utilisation des terres de surface et réduit l'exposition des travailleurs aux polluants. Le matériau réactif le plus utilisé est le fer à valence zéro (ZVI), qui peut dépolluer l'eau souterraine contaminée par une large gamme de contaminants au moyen de mécanismes chimiques et physiques différents. Le problème principal de l'utilisation de ZVI granulaire est la réduction de la porosité du milieu poreux, en raison de la nature expansive de produits de corrosion, des précipités et la formation de gaz. Pour surmonter ce problème, des mélanges de matériaux granulaires et ZVI ont été testés afin de déterminer leur efficacité de dépollution et le comportement hydraulique à long terme. L'utilisation de Lapillus volcaniques à mélanger avec ZVI pour dépolluer les eaux souterraines contaminées par métaux lourds est proposée dans ce travail. Des essais sur Lapillus ont montré une efficacité d'élimination de métaux lourds non négligeable, tandis que les tests en colonne effectuée en utilisant des mélanges n’ont pas montré une réduction élevée de la conductivité hydraulique au cours du temps.La modélisation des essais batch et colonne en tant qu’outil pour la compréhension des mécanismes impliqués dans les milieux poreux réactifs a été mis en place. L’étude de la sensibilité des paramètres des modèles sur leurs réponses a également été explorée. / Groundwater remediation is currently one of the major environmental challenges, considering the number of contaminated sites and the risk posed to human health and to the environment by exposure to groundwater contamination. Permeable reactive barrier (PRB) is a passive in situ technology for the remediation of contaminated groundwater. It consists of a barrier placed perpendicularly to the contaminant flow and made of reactive material that treats contaminant plume flowing through it under the natural hydraulic gradient. It is the most cost-effective groundwater remediation technology; it allows the use of surface land and reduces the exposure of workers to contaminants. The most used reactive material is Zero Valent Iron (ZVI), which is able to remediate groundwater contaminated by a large range of contaminants by means of different chemical and physical mechanisms. The main issue of granular ZVI use regards the reduction of the porous medium porosity, because of the expansive nature of corrosion products, precipitates and gas formation. To overcome this problem, mixtures of ZVI and granular materials were tested to investigate their long-term removal efficiency and hydraulic behavior. The use of volcanic Lapillus to be mixed with ZVI to remediate heavy-metals contaminated groundwater is proposed in this work. Tests on Lapillus showed a not negligible heavy metal removal efficiency of the volcanic material, while the hydraulic monitoring of column tests performed using mixtures showed a not high reduction of hydraulic conductivity over time.Modelling batch and column tests as a tool for understanding the mechanisms involved in the reactive porous media has been set up. The analysis of the sensitivity of the models response with respect to the input parameters has also been explored.

Es wurde eine Arsenkontamination von Boden und Grundwasser im Bereich einer Zellstofffabrik untersucht, die auf Ablagerungen von Eisenoxidschlacken (Rückstände aus der Pyritröstung) mit hohem Gehalt an verschiedenen Spurenelementen zurückzuführen ist. Der Standort ist dadurch gekennzeichnet, dass über viele Jahre Lösungen aus der Celluloseproduktion („Sulfitablauge“) versickerten. Hierdurch gelangten größere Mengen an Sulfat und organischen Stoffen in den Untergrund. Infolgedessen weist das Grundwasser einen stark reduzierten, sulfidischen Chemismus auf. Ein Großteil der Spurenelemente wurde aus der Schlacke im Oberboden in den darunter liegenden wassergesättigten Bereich transportiert und dort in Form von sulfidischen Niederschlägen festgelegt. Eine Ausnahme bildet Arsen, das unter den spezifischen Milieubedingungen im Schadenzentrum lösliche schwefelhaltige Verbindungen bildet (max. 4 mg As/L). Diese Arsen-Schwefel-Spezies wurden erstmals mit einer neu entwickelten IC-ICP/MS- Methode in einem Grundwasser nachgewiesen. Die Grundwasser- und Bodenuntersuchungen sowie begleitende hydrogeologische Messungen ergaben, dass die Arsen-Schwefel-Spezies innerhalb einer Fließstrecke von 30-80 m im Abstrom des Schadenzentrums vollständig immobilisiert werden. Bei der Festlegung von Arsen spielt die biologische Sulfatreduktion, die durch versickerte Sulfitablauge ermöglicht wurde, eine entscheidende Rolle. Anhand dieser Erkenntnisse wurde im Jahr 2000 ein natural attenuation-Konzept zur Sicherung des Standortes ausgearbeitet. Nach Auswertung der Ergebnisse der Standortuntersuchungen aus den Jahren 1999-2005 sowie einer Literaturrecherche zur Arsen-Schwefel-Chemie wurden die Struktur und das Verhalten der unbekannten Arsen-Schwefel-Spezies sowie die Vorgänge bei der Festlegung von Arsen im Boden genauer untersucht. Das wesentlichste Ergebnis der Arbeiten ist, dass in sulfidischen Systemen, z.B. in Grundwässern unter Sulfat reduzierenden Bedingungen, Thioarsenate gebildet werden. In Lehrbüchern und Fachpublikationen aus den vergangenen Jahrzehnten wurde bislang ausschließlich die Existenz von Thioarseniten vermutet. Ursache für die Bildung von Thioarsenaten ist eine hohe Affinität zwischen Arsen und Schwefel, die eine Oxidation von As(III) durch Anlagerung eines Schwefelatoms an dessen freiem Elektronenpaar „erzwingt“. In sulfidhaltigen Lösungen wird hierzu ein Teil des As(III) zu elementarem Arsen reduziert. Das zunächst gebildete Monothioarsenat wird weiter zu den schwefelhaltigeren Thioarsenaten sulfidiert. In sulfidischen Grundwässern bestimmen deshalb die Anionen von Oxomonothioarsenat, Oxodithioarsenat, Oxotrithioarsenat und Tetrathioarsenat das Verhalten von Arsen. Wesentlich für das Verständnis der Arsen-Schwefel-Chemie ist auch die Instabilität der As-SH-Gruppen, die entsprechend dem Dissoziationsverhalten der jeweiligen Arsen-Schwefel-Spezies gebildet werden. Dies erfolgt bei pH-Werten im Bereich von ca. 7-8,5, wobei die monomeren Anionen unter Abspaltung von Schwefelwasserstoff kondensieren. Infolgedessen muss in Grundwässern auch mit polymeren Thioarsenaten gerechnet werden. In saurer Lösung zerfallen die Thioarsenate in arsenige Säure und Schwefel bzw. fallen als Arsenpentasulfid aus. Arsen wird in sulfidischen Aquiferen als Sulfid (z.B. As4S4), als Arsenpyrit (FeAsS) oder durch Einbau von Arsen als Schwefelsubstituent in das Kristallgitter von Mackinawite bzw. Pyrit (FeS, FeS2) festgelegt. Die ermittelten Prozesse können ggf. zur Sanierung bzw. Sicherung von Standorten mit arsenhaltigen Rückständen im Boden bzw. von arsenbelasteten Grundwässern eingesetzt werden. Dabei ist auch von Bedeutung, dass Thioarsenate nach derzeitigem Kenntnisstand relativ gering toxisch sind. Im Umgang mit Thioarsenaten, z.B. auch bei der Analyse von Arsen in sulfidischen Proben, ist jedoch deren Umwandlung in arsenige Säure bei einer pH-Absenkung und auch bei Sauerstoffzutritt zu berücksichtigen. Die biologische Sulfatreduktion spielt eine wesentlich größere Rolle für die Mobilität von Arsen in Grundwässern als bisher angenommen. Im Hinblick auf die weltweit große gesundheitliche Relevanz von Arsen im Trinkwasser und auf mögliche Sanierungsverfahren sollten die Umsetzungen von Arsen unter Sulfat reduzierenden Bedingungen eingehender untersucht werden. / The motivation for the thesis was a project at an industrial site conducted in 1999 to define a remediation concept for soil and groundwater contaminated with arsenic. The contamination resulted from the deposition of residuals from pyrite burning (iron oxides containing different trace elements) in the upper soil many years ago. Because of long-term pollution with process waters rich in organic substances and sulfate, the aquifer is strongly reduced (sulfidic). Most of the arsenic was transferred out of the contaminated soil into the saturated zone in a depth of 7-10 m. There it is partly immobilized as sulfide precipitations, but part of it is solved in the groundwater in form of arsenic-sulfur-complexes (up to 4 ppm). These complexes were detected for the first time in a groundwater by means of an improved IC-ICP-MS method. It was also found that approx. 80 m downstream of the contaminated spot the concentrations of arsenic in soil and groundwater were not increased. On this basis a natural attenuation concept was proposed in 2000. The data from the investigated site was evaluated and specific laboratory tests were carried out in order to identify the unknown arsenic species as well as the processes which lead to their immobilization in the aquifer. The key role of the soluble arsenic-sulfur complexes for the mobility and toxicity of arsenic in sulfate-reducing environments is commonly accepted. In the past, thioarsenites were assumed to be the existing species in sulfidic systems. In this study, however, thioarsenates were identified in solutions spiked with in arsenite and hydrogen sulfide as well as in the contaminated groundwater. The unexpected finding of an oxidation of arsenite to thioarsenates in strongly reducing systems can be explained by the high affinity between As(III) and sulfur. In sulfide containing solutions without any oxidant, arsenite therefore undergoes disproportionation to thioarsenates and elemental arsenic. This was already found out in the 19th century, but has been neglected in publications from the last decades. According to the results of this study the anions of oxomonothioarsenate, oxodithioarsenate, oxotrithioarsenate und tetrathioarsenate are the dominating arsenic species in sulfidic waters. The partitioning of the four species is governed mainly by the sulfide concentration. Beside the high affinity between arsenic and sulfur, the instability of the As-SH group is essential to understand the reactions in the arsenic-sulfur system. As soon as the arsenic-sulfur complexes form As-SH groups (according to their dissociation characteristics) they condensate in separating hydrogen sulfide. Thioarsenates form polymers in the pH range of approx. 7-8.5. Therefore beside the mentioned monomers, thioarsenate polymers can also be important in natural environments. In more acidic solutions they decay into arsenite and sulfur or precipitate as arsenic-pentasulfide. When analyzing arsenic in sulfide containing solutions, it has always to be taken into account that thioarsenates are highly sensitive to oxygen and pH. Therefore, e.g. arsenic speciation by means of HG-AAS is not suitable for sulfidic waters and can wrongly indicate a mixture of arsenite and arsenate. It has previously been supposed that the mobility as well as the toxicity of arsenic increase if the redox state decreases. For sulfidic waters the opposite is probably the case owing to the formation of thioarsenates. The toxicity of arsenite is due to the high reactivity of the As(III) towards sulfohydroxyl groups in proteins. Without a free electron pair and sulfur already incorporated, thioarsenates should be less toxic compared to arsenite. Arsenic can be mobilized out of contaminated soils in form of thioarsenates via infiltration of sulfide solutions or by input of sulfate and biodegradable organic matter. In the presence of iron, thioarsenates can be fixated in sulfidic aquifers as a minor substitute in mackinawite and biogenic pyrite or as arsenic pyrite. Bacterial sulfate reduction is a crucial factor for the mobilization and immobilization of arsenic in reduced aquifers. Considering the negative health impacts of arsenic for millions of people worldwide, as well as the implementation of the mentioned remediation strategies the arsenic-sulfur chemistry deserves closer attention.

No description available.

No description available.