Mineral oils and coal tars are complex nonaqueous phase liquids (NAPLs), which can serve as long-term sources of ground water contamination. Very limited data are available on mineral oil and coal tar entrapment in and removal from porous media. Thus, the objectives of this research were to evaluate the behavior of these NAPLs in porous media, and investigate the mechanisms governing NAPL entrapment in and recovery from porous media. Quantification of properties of three commercial mineral oils and six MGP coal tars reveals that mineral oils are slightly viscous LNAPLs (density: ~0.88 g/cm3; viscosity: 10-20 cP), whereas coal tars are highly viscous DNAPLs (density: 1.052-1.104 g/cm3; viscosity: 32-425 cP). Measured oil (tar)-water interfacial tensions (IFT) were lower than that of pure NAPLs. Properties of 16 field soil samples (soil particle size distribution, specific surface area, total carbon content, cationic exchange capacity and soil moisture release curves) were characterized. Correlations between residual NAPL saturation and NAPL and soil properties were developed, and show that the entrapment of NAPL dependent upon soil particle size distribution, total carbon content, NAPL viscosity and NAPL-water IFT. Aqueous pH and ionic strength were found to influence the interfacial properties in tar-water-silica systems. At pHs greater than 7.0, observed reduction in contact angle were attributed to the repulsive electrostatic force between coal tar and solid surface. When pH less than 4, hydration forces played a role on the contact angle decrease. The IFT reduction was resulted from the accumulation of surface-active molecules at the tar-water interface. The effect of ionic strength on interfacial properties was not significant below 0.5 M. The effects of temperature and surfactant or surfactant/polymer addition on coal tar removal was investigated by conducting coal tar displacement experiments at three different temperatures (22, 35, and 50??with sequential flushing of water, surfactant and surfactant/polymer. Coal tar removal from porous media was enhanced by elevating temperature and surfactant flushing due to the viscosity and IFT reduction, respectively. Xanthan gum was used as the polymer to increase the viscosity of the displacing fluid. In summary, these results provide tools for the prediction of NAPL entrapment in porous media, and for the selection of remediation strategies for coal tar contaminated source zone.

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.

The industrial solvent trichloroethylene (TCE) and petroleum hydrocarbons (e.g., fuel oil) are among the most ubiquitous organic compounds found in subsurface contaminated environment. The developed treatment train system included the first stage of groundwater and surfactant flushing followed by the second stage of chemical oxidation such as potassium permanganate (KMnO4) and Fenton-like treatment. The third stage was the application of enhanced bioremediation for the further removal of residual contaminants after the first two treatment processes. The objectives of this study were to (1) assess the applicability of treatment train system for the remediation of organic compounds contaminated subsurface environment, (2) determine the optimal operational conditions of the three-stage treatment system, and (3) evaluate the effects of residual surfactant Simple GreenTM (SG) and hydrogen peroxide (H2O2) after chemical oxidation stage on the efficiency of bioremediation process. In this study, three different surfactants [SG, Triton X-100, and Tween 80] were evaluated in batch experiments for their feasibility on contaminants removal. Results from the surfactant biodegradation and microbial enumeration study indicate that SG was more biodegradable and was able to enhance the microbial activity of the intrinsic microorganisms. Thus, SG was applied in the following batch or column experiments of the treatment train system. Results from this study indicate that approximately 87.6% of TCE in the system (with initial concentration of 40 mg L-1) could be removed from the simulated dense non-aqueous-phase liquids (DNAPLs) system after groundwater flushing followed by biodegradable surfactant (1 g L-1 of SG) flushing, while the TCE concentrations dropped from 40 to 4.96 mg L-1 at the end of the flushing experiment. Moreover, approximately 10.7% of the remaining TCE could be removed from the system after the oxidation process using KMnO4 as the oxidant. Results from the oxidation process show that TCE was reduced from 4.96 to 0.69 mg L-1, and chloride concentation was increased from ND to 0.88 mg L-1 with the presence of 1 g L-1 of SG. The residual 1.7% of the TCE could be further remediated via the enhanced bioremediation stage, and the TCE concentrations dropped from 0.69 mg L-1 to below detection limit at the end of the bioremediation experiment. Results also indicate that the remaining KMnO4 had no significant inhibition on bacterial growth and TCE biodegradation. Thus, SG flushing and KMnO4 oxidation would not cause adverse effect on subsequent bioremediation process using intrinsic bacteria. Thus, complete TCE remediation was observed in this study using the three-stage treatment scheme. Results from the column experiment reveal that a complete TPH removal could be obtained after the application of three consecutive treatment processes. Results show that TPH concentration could be reduced from 50,000 mg kg-1 to below detection limit. This indicates that the treatment train system is a promising technology to remediate fuel-oil contaminated soils. Results from the column study indicate that approximate 80.3% of initial TPH in the soil could be removed after the SG [50 pore volumes (PVs)] followed by groundwater (30 PVs) flushing. The Fenton-like oxidation (with 6% of H2O2 addition) was able to remove another 15.0% of TPH. The observed first-order reaction rate constant of TPH oxidation was 2.74¡Ñ10-2 min-1, and the half-life was 25.3 min during the first 40 min of reaction. The residual 4.7% of the TPH could be further remediated via the aerobic bioremediation process. Thus, complete TPH removal was obtained in this study using the three-stage treatment scheme. The proposed treatment train system would be expected to provide a more efficient and cost-effective alternative to remediate chlorinated solvent and petroleum hydrocarbons contaminated sites.

De nos jours, la préservation de l’environnement est un enjeu majeur. Avant cette prise de conscience, de nombreux polluants ont été rejetés dans la nature. Parmi eux, les hydrocarbures sont très souvent rencontrés. Or, ils sont reconnus pour leur toxicité et leur persistance accrue. La mise en place de méthodes efficaces de dépollution est donc primordiale. Les méthodes classiques nécessitent l’excavation ou le pompage des zones contaminées, imposant un coût de dépollution élevé. C’est pourquoi des techniques de dépollution in-situ ont été développées afin de réduire ces coûts, tout en garantissant des rendements de dépollution efficaces. Les travaux menés durant cette Thèse ont permis de déterminer, pour plusieurs techniques de traitement, les facteurs limitants inhérents à la technique, mais aussi de quantifier le rôle du contact entre agents de traitement et zone polluée ou des effets densitaires. Les techniques in-situ utilisées sont : l’oxydation chimique in situ, le lavage par tensio-actifs, l’injection d’air (sparging) et le traitement thermique. Trois niveaux d’expérience ont été étudiés : le batch, la colonne et le pilote 3D. Les réacteurs fermés, ont permis la comparaison des oxydants en statiques face à une matrice plus ou moins riche en matières organiques. Les colonnes ont mis en avant l’influence du mode d'injection appliqué vis-à-vis des propriétés physico-chimiques des polluants (cinétique réactionnelle, pression de vapeur, température d’ébullition, etc.). Les pilotes 3D, d’un volume d’un 1 m3, ont permis de comparer les différentes techniques sur un milieu hétérogène présentant des zones peu perméables, difficiles à traiter. A partir des résultats acquis et de modélisation numérique des expériences, il est dorénavant possible de mieux ajuster la méthode de traitement et surtout de comparer différentes méthodes pour un contexte hydrogéologique donné. / Pollution of soils and aquifers by Diesel fuel compounds is a widespread remediation issue. Problems due to soil remediation are more and more difficult to treat. Hydrocarbons are often encountered. But they are known for their toxicity and increased persistence. The establishment of effective remediation methods is paramount. Conventional methods require excavation or pumping contaminated areas requiring a high abatement costs. That is why, in-situ remediation techniques have been developed to reduce these costs while ensuring efficient pollution control returns. The work done during this thesis has determined for several treatments, the limiting factors inherent the treatment, but also quantifies the role of contact between agents and pollutants or density effects. In-situ treatments are: in situ chemical oxidation, surfactants flushing, air sparging and thermic treatment. Three levels of experience were investigated: batch, column and 3D Pilot. Batchs, enabled the comparison of oxidants in sand and natural soil. The columns have highlighted the influence of the injection method applied occurs toward the physical and chemical properties of contaminants (reaction kinetics, vapor pressure, boiling temperature, etc.). 3D Pilot, have a volume of 1m3. They were used to compare the different treatments on a heterogeneous medium having low permeability zones, difficult to treat. From the results of numerical modeling and experiences, it is possible to adjust the treatment method and especially to compare different methods for a given hydrogeological context.