The problems associated with the contamination of groundwater environments by non-aqueous phase liquids (NAPLs) such as chlorinated solvents, gasoline and manufacturing gas plant (MGP) residuals, including their distribution and persistence, are well accepted. The treatment of groundwater by in situ chemical oxidation (ISCO) relies on the oxidation potential of chemical reagents to destroy harmful organic compounds. The interaction of these oxidants with target and non-target compounds in the subsurface will help determine effectiveness and efficiency of an ISCO treatment system. Push-pull tests (PPTs) have the utility to estimate key properties in situ and allow for sampling a larger volume of aquifer to yield more representative estimates as compared to conventional bench-scale tests. The scale and cost-effectiveness of a PPT make it an ideal tool to collect valuable information on subsurface system behaviour so that uncertainties can be minimized. The use of PPTs to provide insight into treatment expectations or to support the design of an ISCO system requires a suitable interpretation tool. A multi-species numerical model (‘PPT-ISCO’) in a radial coordinate system was developed to simulate a PPT with the injection of a conservative tracer and oxidant (persulfate or permanganate) into the saturated zone of a porous medium environment. The pore space may contain variable amounts of immobile, multicomponent, residual NAPL. The aquifer material contains a natural organic matter (NOM) fraction and/or other oxidizable aquifer material (OAM) species. The model is capable of simulating mass transport for an arbitrary number of conservative and reactive tracers and NAPL constituents subjected to chemical reactions. The ability of PPTs to capture the in situ natural oxidant interaction (NOI) was tested with PPTISCO. Breakthrough curve (BTC) data collected from permanganate and persulfate PPTs conducted in the field were compared to simulated BTCs by assigning the same field operational parameters to the model and applying NOI kinetic information obtained from batch tests. These tests confirmed the usability of the model and PPTs to obtain the NOI kinetics from PPT BTCs. The sensitivity of PPT BTCs to variations in the field operating and NOI parameters were investigated. The results of varying the field operating parameters indicated that the oxidant BTCs could be scaled to match varying injection and extraction flow rates. Variations in NOI parameters revealed that the permanganate BTC is primarily controlled by the permanganate fast reaction rate coefficient and the quantity of OAM present in the aquifer. The spatial profiles of OAM across the test zone revealed that the majority of the OAM consumption is from the fast fraction and occurs in the vicinity of the well where the permanganate concentration is greatest. An estimate of the permanganate fast reaction rate coefficient can be obtained from a permanganate PPT BTC by employing the model to simulate the PPT with the operational parameters (used in the field) and literature estimates of the remaining NOI parameters. Calibration between the simulated and observed BTCs can be undertaken to adjust the permanganate fast reaction rate coefficient to fit the permanganate PPT BTC. Persulfate NOI sensitivity investigations revealed that persulfate PPT BTCs can be characterized by a concentration plateau at early times as a result of the increased ionic strength in the area around the injection well. The ionic strength is primarily controlled by the injected persulfate concentration, and as persulfate degrades into sulphate and acid, the ionic strength is enhanced. Graphical analysis of the BTC revealed that an underestimated value of the persulfate degradation rate coefficient can be obtained from the PPT BTC. A more representative estimate of the persulfate degradation rate coefficient can be achieved after fitting the field BTC to the simulated results, applying the underestimated value as a starting point. PPTs investigating ISCO treatability have the ability to provide insight into the effect of the NOI on the oxidation of target compounds, site-specific oxidant dosage requirements and NAPL treatment expectations. NAPL component BTCs from treatability PPTs are primarily controlled by the mass in the fast region, and the fast region mass transfer rate coefficient. Oxidation estimates extracted from NAPL component BTCs were shown to accurately approximate the mass of each NAPL component oxidized when compared to model calculations. The mass of NAPL oxidized for each of the components yields a site-specific oxidant dosage. This estimate exceeds what is prescribed by the stoichiometry between permanganate and the contaminant of concern due to the effect of the NOI. The utility of PPTs to study and quantify the interaction between injected oxidants and the aquifer material has been demonstrated with PPT-ISCO. In addition, PPT-ISCO has revealed that treatability PPTs can be tailored to investigate the dosage requirements and treatment expectations of residual NAPLs. Results from this effort will be used to support ongoing field research exploring the use of PPTs to assist in understanding the competing subsurface processes affecting ISCO applications.

The problems associated with the contamination of groundwater environments by non-aqueous phase liquids (NAPLs) such as chlorinated solvents, gasoline and manufacturing gas plant (MGP) residuals, including their distribution and persistence, are well accepted. The treatment of groundwater by in situ chemical oxidation (ISCO) relies on the oxidation potential of chemical reagents to destroy harmful organic compounds. The interaction of these oxidants with target and non-target compounds in the subsurface will help determine effectiveness and efficiency of an ISCO treatment system. Push-pull tests (PPTs) have the utility to estimate key properties in situ and allow for sampling a larger volume of aquifer to yield more representative estimates as compared to conventional bench-scale tests. The scale and cost-effectiveness of a PPT make it an ideal tool to collect valuable information on subsurface system behaviour so that uncertainties can be minimized. The use of PPTs to provide insight into treatment expectations or to support the design of an ISCO system requires a suitable interpretation tool. A multi-species numerical model (‘PPT-ISCO’) in a radial coordinate system was developed to simulate a PPT with the injection of a conservative tracer and oxidant (persulfate or permanganate) into the saturated zone of a porous medium environment. The pore space may contain variable amounts of immobile, multicomponent, residual NAPL. The aquifer material contains a natural organic matter (NOM) fraction and/or other oxidizable aquifer material (OAM) species. The model is capable of simulating mass transport for an arbitrary number of conservative and reactive tracers and NAPL constituents subjected to chemical reactions. The ability of PPTs to capture the in situ natural oxidant interaction (NOI) was tested with PPTISCO. Breakthrough curve (BTC) data collected from permanganate and persulfate PPTs conducted in the field were compared to simulated BTCs by assigning the same field operational parameters to the model and applying NOI kinetic information obtained from batch tests. These tests confirmed the usability of the model and PPTs to obtain the NOI kinetics from PPT BTCs. The sensitivity of PPT BTCs to variations in the field operating and NOI parameters were investigated. The results of varying the field operating parameters indicated that the oxidant BTCs could be scaled to match varying injection and extraction flow rates. Variations in NOI parameters revealed that the permanganate BTC is primarily controlled by the permanganate fast reaction rate coefficient and the quantity of OAM present in the aquifer. The spatial profiles of OAM across the test zone revealed that the majority of the OAM consumption is from the fast fraction and occurs in the vicinity of the well where the permanganate concentration is greatest. An estimate of the permanganate fast reaction rate coefficient can be obtained from a permanganate PPT BTC by employing the model to simulate the PPT with the operational parameters (used in the field) and literature estimates of the remaining NOI parameters. Calibration between the simulated and observed BTCs can be undertaken to adjust the permanganate fast reaction rate coefficient to fit the permanganate PPT BTC. Persulfate NOI sensitivity investigations revealed that persulfate PPT BTCs can be characterized by a concentration plateau at early times as a result of the increased ionic strength in the area around the injection well. The ionic strength is primarily controlled by the injected persulfate concentration, and as persulfate degrades into sulphate and acid, the ionic strength is enhanced. Graphical analysis of the BTC revealed that an underestimated value of the persulfate degradation rate coefficient can be obtained from the PPT BTC. A more representative estimate of the persulfate degradation rate coefficient can be achieved after fitting the field BTC to the simulated results, applying the underestimated value as a starting point. PPTs investigating ISCO treatability have the ability to provide insight into the effect of the NOI on the oxidation of target compounds, site-specific oxidant dosage requirements and NAPL treatment expectations. NAPL component BTCs from treatability PPTs are primarily controlled by the mass in the fast region, and the fast region mass transfer rate coefficient. Oxidation estimates extracted from NAPL component BTCs were shown to accurately approximate the mass of each NAPL component oxidized when compared to model calculations. The mass of NAPL oxidized for each of the components yields a site-specific oxidant dosage. This estimate exceeds what is prescribed by the stoichiometry between permanganate and the contaminant of concern due to the effect of the NOI. The utility of PPTs to study and quantify the interaction between injected oxidants and the aquifer material has been demonstrated with PPT-ISCO. In addition, PPT-ISCO has revealed that treatability PPTs can be tailored to investigate the dosage requirements and treatment expectations of residual NAPLs. Results from this effort will be used to support ongoing field research exploring the use of PPTs to assist in understanding the competing subsurface processes affecting ISCO applications.

L'effet de l'hétérogénéité du milieu physique sur le transport de solutés dans les eaux souterraines est bien connu, mais le couplage avec les processus biochimiques en milieu hétérogène est un problème plus complexe générant des processus non linéaires dépendants de la nature du milieu et des cinétiques de réactions. Certaines réactions telles que la dénitrification font intervenir une activité biologique pour laquelle l'influence des conditions de transport reste peu connue. Cette étude cherche à caractériser l'influence des vitesses d'écoulement sur la réactivité. Les mécanismes contrôlant les processus biogéochimiques sont dépendants de l'échelle d'étude. A l'échelle d'un tube de diamètre 2 mm, où une réaction de dénitrification s'opère sous différentes contraintes d'écoulement, les expériences montrent tout d'abord un contrôle biologique de la réactivité qui devient par la suite un contrôle physique pouvant s'expliquer par des phénomènes de diffusion au sein du biofilm formé. A l'échelle d'un milieu poreux ces travaux ont permis d'identifier une réaction de dénitrification incluant de la biotite comme donneur d'électron. A l'échelle du site des essais de push-pull ont permis de quantifier les cinétiques de dégradation des nitrates ainsi que les cinétiques de production des sous produits de réaction tels que le protoxyde d'azote. Ces informations permettent d'estimer l'influence de cette réaction à l'échelle du site. Ces travaux permettent d'améliorer des connaissances sur la réactivité dans les aquifères à différentes échelles.

Les processus microbiens ont une importance déterminante dans la dynamique des processus réactifs dans les eaux souterraines. La compréhension de la variabilité spatiale et temporelle de ces phénomènes, et le développement de méthodes expérimentales de terrain, ouvrent de nouveaux champs de recherches et d'applications allant de la remédiation des aquifères contaminés à la compréhension des grands cycles biogéochimiques naturels. Dans le premier volet de cette thèse nous présentons des observations de terrain permettant de comprendre le rôle des fractures sur la formation d'un ''hotspot'' d'activité microbienne en profondeur. Du fait de leur forte réactivité, ces ''hotspots'' peuvent dominer la dynamique biogéochimique des milieux souterrains, malgré leur faible extension spatiale. Nous avons ainsi analyser les conditions de formation d'un tapis microbien par des bactéries ferro-oxydantes à 60 mètres de profondeur sur l'observatoire de Ploemeur (réseau H+) alors que ces phénomènes ont été observé jusqu'à présent en surface. Les résultats de cette étude montrent que des circulations hétérogènes, liées à la structure des milieux fracturés, créent des zones mélanges entre des eaux riches en fer et des eaux oxygénées, à l'origine de ce hotspot microbien. Le deuxième volet de ce travail de thèse a été consacré au développement d'une méthode innovante pour la mesure en continu de l'activité microbienne dans les eaux souterraines. La méthode est basée sur l'utilisation de la Fluoréscéine DiAcétate (FDA) dont le produit de réaction peut être mesuré en continu par un fluorimètre de terrain. Après avoir testé et validé les protocoles sur des solutions enzymatiques et des eaux naturelles en laboratoire, nous avons mis en œuvre cette technique sur le terrain au cours d'expériences de traçages réactifs. Un modèle cinétique nous a permis d'approcher les résultats obtenus en laboratoire, et de comparer nos résultats de terrain aux calibrations effectuées in vitro. Cette méthode ouvre ainsi de nouvelles perspectives pour la caractérisation des processus biogéochimiques sur le terrain. / Microbial processes play a key role in controlling biogeochemical reactivity in groundwater. The understanding of the spatial and temporal variability of these phenomena and the development of novel experimental field methods, has opened new fields of research and applications, ranging from groundwater remediation to understanding of global biochemical cycles. In the first part of this thesis, we present field observations providing new insights on the role of fractures in the formation of a hotspot of microbial activity. Because of their large reactivity, these hotspots can dominate the biogeochemical dynamics of subsurface systems, despite their small spatial extent. We have thus analyzed the conditions for the formation of a microbial mat composed of iron-oxidizing bacteria at 60 meters depth in the Ploemeur fractured rock observatory (H+ network) while these phenomena are usually observed at the surface. These results show that heterogeneous flowpaths, linked to the structure of fractured media, create mixing zones between iron rich water and oxygen rich water, at the origin of the microbial hotspot. The second part of this work was devoted to the development of a novel method for a continuous measurement of microbial activity in groundwater. The method is based on the use of Fluorescein DiAcetate (FDA) whose product of reaction can be measured continuously by a field fluorimeter. After testing and validating protocols in the lab on enzymatic solutions and natural water, we have implemented this technic in the field in reactive tracer test experiments. A kinetic model allowed us to interpret the lab results, and to compare them to the field kinetics. This method thus opens new perspectives for the characterization of biogeochemical processes in the field.