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The research was driven by questions pertaining to the vulnerability and protection of public water supply wells in fissured and karstic aquifers. The requirement of the industrial and research communities for highly detectable and non-toxic ground water tracers was addressed through the development of Sulphur Hexafluoride (SF6) for this purpose. This dissolved gas tracer exhibits similar physico-chemical properties to the chlorofluorocarbons (CFCs), and these hydrologic tracers were examined together in their respective capacities as applied (i.e. injected) and environmental (already present) groundwater tracers. Public water supply wells in the Corallian limestone of Yorkshire, England, were used to test the application of SF6- A hydrogeological conceptualisation of the system prior to use of the experimental technique was built from the results of geophysical borehole logging, single-borehole dilution tests and forced and non-forced gradient (dye) tracer tests. The novel tracer SF6 was injected into a karst swallet draining the River Derwent and was tracked for 44 days to a dilution 2 x 10 times smaller than the injected concentration, and still 100 times above background. The SF6 results enabled specific elements of the conceptual model to be stated theoretically and compared directly with data for the purposes of discriminating between different processes potentially operative within the aquifer. These comparisons included an analysis of breakthrough curve (BTC) tailing as a function of a geohydrological dipole, hydrodynamic dispersion as a function of tracer transport along multiple pathways (fissures and karstic conduits), and the effects of double-porosity diffusion. Paradoxical observations between rates of tracer transport and apparent groundwater ages obtained by applying simple piston-flow models to measured CFC concentrations indicated additional processes within the aquifer. The Corallian CFC survey was supported by a detailed examination of the largest local source of CFC contamination in the area, an operational landfill site situated above the aquifer.

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No description available.

No description available.

The natural attenuation of groundwater pesticides by biological degradation, is widely accepted to occur at concentrations > 1 mg 1-1. However from observations of groundwater monitoring data it can be indicated that the occurrence of pesticides in groundwater is primarily at trace μg 1-1 concentrations, with 45 % of UK groundwater samples that failed the EC Drinking Water Directives PV of 0.1 μg 1-1 between 1995 – 2000, accounting for an average concentration of 64 μg 1-1. However, there are limited directed studies of in situ biological degradation of pesticides at μg concentrations. Therefore, this work was designed provided an insight as to whether any prevalent microbial adaptation can occur to degrade atrazine at μg 1-1 concentrations in groundwater. Laboratory batch studies were performed using a groundwater exposed to 0.2 μg 1-1 of the herbicide atrazine, for an excess of 10 years. Bacterial enrichment using a glucose minimal salts medium resulted in no biological degradation of atrazine, when amended at concentrations between 10 μg to 50 mg 1-1. Batch studies using the atrazine degrader Pseudomonas sp. Strain ADP as a positive control, indicated a capability to degrade atrazine within sterilised groundwater, at 50 mg 1-1 (0.92 mg 1-1 day-1) and 1 mg 1-1 (0.14 mg 1-1 day-1), but no degradation of atrazine at 100 or 10 μg 1-1. Therefore, biological degradation of trace μg 1-1 concentrations of atrazine by groundwater in situ bacteria does not readily occur. It is expected that changes in atrazine groundwater concentrations, are resulting purely from dilution, sorption or chemical degradation. Consequently, it cannot be assumed that microbial adaptation can occur to degrade atrazine at μg 1-1 concentrations in groundwaters even if in situ bioaugmentation methods are applied.

Les eaux souterraines du système aquifère complexe volcano-sédimentaire, exploité pour l’alimentation en eau potable de Djibouti-ville, connaissent une dégradation de leur qualité face à une croissance démographique élevée, un exode rural, une désertification qui s’accentuent dans un contexte à climat aride sévère. Cette dégradation s’exprime par la salinisation et la contamination des eaux en relation directe avec la surexploitation. Les données hydrogéochimiques ont été analysées en utilisant une combinaison de méthodes géochimiques et statistiques pour évaluer la qualité afin de connaitre les processus géochimiques contrôlant la chimie des eaux. L’étude a montré une variété d’origines et de processus de salinisation des eaux. Notre étude a démontré que l’anomalie de forte salinité est certainement due au phénomène d’intrusion marine. Le mélange des eaux de la nappe avec de l’eau de mer est justifié par les fortes teneurs en chlorures due à une proportion d’eau de mer significative. Cependant, la salinité est acquise par la contribution d’une autre source d’eau salée provenant de la remobilisation d’une eau salée ancienne probablement piégée dans les scories. Cette source est différente de l’eau de mer actuelle par son cortège cationique, et correspond à une eau de mer modifiée par l’interaction avec le basalte. L’étude a permis de mettre en évidence que les réactions d’échanges cationiques inverse liées à l’intrusion marine et les processus de dissolution géochimiques sont les caractéristiques géochimiques des eaux contaminées par les eaux marines. L’étude de la qualité chimique des eaux, montre des teneurs excessives en éléments majeurs dépassant largement les seuils autorisés. Les teneurs en éléments traces (Se, As) montrent une contamination importante dans les eaux de la plaine côtière. L’augmentation de ces éléments est probablement due à l’influence des formations volcaniques et est accentuée par l’intrusion saline, liée à une exploitation intensive. / Subterranean waters of the complex volcano-sedimentary aquifer system, exploited for drinking water supply of the Djibouti capital, undergo a degradation of their quality faced with high population growth, rural exodus, desertification which is accentuated in a context to severe arid climate. This degradation expresses itself by the salinization and the contamination of waters in direct relation with the overexploitation. The hydrogeochemical data were analyzed by using a combination of classic and statistical geochemical methods to estimate the quality in order to recognize the geochemical processes governing the chemistry of subterranean waters. The study indicated a variety of origins and processes of waters salinization. Our study has demonstrated that the anomaly of strong salinity is certainly due to the phenomenon of marine intrusion. The mixture of the groundwater sheet with some sea water is justified by the strong contents in chlorides. However, salinity is acquired by the contribution of another source of salt water resulting from the remobilization of old salt water, probably trapped in scorias. This second source of chlorinated water, is different from some current sea water by its cationic procession, and would correspond to sea water modified by the interaction with the basalt. Our study allowed highlighting that the reactions of inverse cationic exchange bounded to the marine intrusion and the geochemical dissolution processes are the geochemical characteristics of waters contaminated by marine waters. The study of the chemical water quality of various aquifers shows excessive contents in major elements exceeding widely the authorized thresholds. The contents in trace elements (Se, As) show an important contamination of groundwater of the coastal plain. The increase of the toxic elements is probably due to the influence of the volcanic formations and is stressed by the salt intrusion, related to an intensive exploitation.

L' augmentation de la population à Tripoli et ses environs a conduit une augmentation de la demande des eaux souterraines et le forage de puits aléatoire . Cette situation a entraîné une hausse de la demande d'eau souterraine et ainsi a mit en danger l' aquifère (Miocène), ce qui peut entraîner des problèmes graves à moins des étapes pour la gestion des ressources en eau sont mises en œuvre . Ces mesures devraient inclure la définition de la caractérisation rigoureuse des propriétés de l'aquifère afin de bien gérer la qualité et la quantité d'eau pompée. Notre objectif dans cette étude est d'analyser les paramètres hydrochimique, hydrophysique, ainsi que le niveau d'eau de la nappe phréatique de Karstique du Nord du Liban. La répartition spatiale des paramètres physico- chimique obéit à une tendance croissante vers l'ouest c'est à dire vers la mer Méditerranée. Au cours des dernières décennies, les eaux souterraines illégalement pompé pour l'usage domestique et agricole a entraîné une dégradation de la qualité des eaux souterraines en raison de l'intrusion saline de l'eau dans les zones occidentales. Afin d'étudier l'origine le logiciel PhreeqC a permis de déterminer les propriétés et l'aspect hydrochimique des eaux souterraines ; de même le logiciel Aquitest a permit d'etudier les niveau d'eau de la region. SIG, Surfer et Visual MODFLOW ont été utilisés pour générer des cartes de localisation de la distribution spatiale des paramètres ainsi que la modélisation de la carte potentiométrique. Le résultat final a été la détermination des sources anthropiques, naturogéniques de contamination de l'eau au Nord du Liban et la formation de la carte piézométrique de la région. / The increasing population in Tripoli and its surrounding has placed an increase in the demand of groundwater and the random drilling of wells. This situation has resulted in a higher demand of groundwater and thus endangered the Miocene aquifer that will cause problems unless serious steps for the management of water resources are implemented. These steps should include defining stringent characterization of the properties of the aquifer in order to properly manage the quality & quantity of pumped water.Our aim in this study is to analyze the hydrochemical, hydro physical quality,& water level of groundwater in the Miocene aquifer in the North of Lebanon. The results have shown that the dominant type of groundwater in the area is highly chlorinated with sulfated calcium and magnesium with heavily charged Nitrate & Nitrite. The spatial distribution of the physiochemical parameters obey an increasing pattern westwards towards the Mediterranean Sea. During the last decades, illegal groundwater pumping mainly for domestic and agricultural use has caused groundwater quality degradation due to saline water intrusion from western areas .In order to study the origin and the hydrochemical aspect of groundwater, Phreeq C & Diagram software helped us determine the properties ;as for the water level Aquitest software was used.GIS ,Surfer & Visual Modflow softwares were used to generate maps locating the spatial distribution of all parameters & most importantly the modeling of the potentiometric map of the North. The end result was the determination of anthropogenic & naturogenic sources of water pollution in the North of Lebanon & the formation of the piezometric map of the region.

This work examined the impact of soil organic matter (SOM) on the sorption, phase distribution and transport of ethanol and butanol blended gasoline vapours after release. Microcosm and mini-lysimeter experiments were conducted using sand with varying SOM and moisture contents. Synthetic gasoline alone and blended with 10 - 20% ethanol and 10 - 20% butanol by volume, referred to as UG, E10 - E20 and B10 - B20, respectively, were used. Results from the UG were used as the benchmark to assess the impact of ethanol and butanol on gasoline compounds. The findings of this work illustrate the likely behaviour of gasoline compounds at the beginning times of a gasoline spill or leak. The addition of alcohol to gasoline altered the behaviour of the gasoline compounds in the vadose zone in several ways. Firstly, it reduced the sorption of the gasoline compounds by soils. This effect was greatest on the first day of a spill and affected the gasoline compounds in decreasing order of hydrophobicity. Secondly, it altered the mass distribution of the gasoline compounds between the vadose zone phases to higher mass compounds in the mobile phases (soil air and soil water) and lower mass compounds in the immobile soil solid phase, suggesting higher risk of groundwater contamination with an increasing content of alcohol in the gasoline. Thirdly, it increased the vapour phase transport of the gasoline compounds from the source zone to the groundwater zone. These three impacts were generally greater for ethanol than butanol. The sorption coefficients (Kd) of E20 gasoline compounds were reduced by 54% for alkanes, 54% for cycloalkanes and 63% for the aromatics, while the Kd of B20 gasoline compounds decreased by 39% for alkanes, 38% for cycloalkanes and 49% for aromatics. This implies that the use of ethanol as gasoline oxygenate could result in greater risk of groundwater contamination with gasoline compounds than the use of butanol after spills. The SOM enhanced the sorption of alcohol-blended gasoline compounds in soils. This impact was similar for ethanol and butanol blended gasoline as the Kd of B20 and E20 were equally increased by 7 times for aromatics, 4 times for cycloalkanes and 2 times for alkanes, for 0 to 5% increase in the SOM fraction of sand. Although SOM enhanced the sorption of alcohol-blended gasoline, its sorptive capability was not fully realised compared with the sorption of the UG compounds. Also, it did not alter the order of groundwater contamination risk for the ethanol and butanol blended gasoline. Thus, the Kd values for all gasoline compounds for all the SOM fractions tested, including 0%fom, 1%fom, 3%fom and 5%fom, were in the order of UG>B20>E20, indicating greater risk of groundwater contamination for the ethanol-blended gasoline after a spill or leak regardless of the SOM content of the soil. The increase in the water content of soil reduced the sorptive capability of SOM and affected the overall mass distribution of gasoline compounds between the soil solid, soil air and soil water phases estimated with values of Henry’s law constant from the literature. This indicates that the degree of gasoline retention in the vadose zone by SOM could differ during the dry summer and wet winter seasons. This effect was greater for ethanol than butanol. Thus, in all seasons, the amount of gasoline compounds retained by SOM in the vadose zone is likely to be higher for butanol-blended gasoline than ethanol-blended gasoline. Overall, this study indicates that the use of high ethanol volume in gasoline to combat climate change may put the groundwater at greater risk of contamination after spills or leakages from storage. Therefore, to successfully reduce greenhouse gases emissions via high alcohol volume in gasoline and still protect the world’s groundwater resource, this study suggests the use of butanol is more benign than ethanol.

Ce travail de thèse propose un modèle numérique complet pour l'écoulement transitoire des eaux souterraines dans les milieux poreux et fracturés et son application sur l’analyse de la stabilité des pentes sous l’effet d’une diminution du niveau de l’eau dans un réservoir. L’écouement de l’eau dans les milieux fracturés est complexe, en raison de la présence d'un grand nombre de fractures et de fortes variations dans les propriétés géométriques et hydrauliques de ces milieux.La thèse est organisée en six chapitres.Le premier chapitre pésente les problèmes abordés et les objectifs de la thèse. Le 2nd chapitre présente une synthèse des analyses numériques de l'écoulement dans les milieux fracturés et de ses effets sur la stabilité des pentes. Le 3ème chapitre présente le développment d’un modèle numérique d'écoulement transitoire saturé dans des milieux fracturés avec une surface libre en utilisant la méthode des éléments composites (CEM). Le 4ème chapitre présente un modèle numérique d'écoulement transitoire à saturation variable, dans les milieux fracturés à l'aide du CEM.Le 5ème chapitre présente une étude de la stabilité des pentes sous l’effet de variation des paramètres hydrauliques et de résistance des sols, et da géométrie des pentes.Le 6ème chapitre présente une étude paramétrique de l'influence des caractéristiques de fracture sur l'écoulement transitoire et la stabilité d’une pente soumise à des conditions de diminution. / This thesis presents a comprehensive numerical method for analyzing transient groundwater flow in porous and fractured media and its application to the analysis of the stability of soil and rock slopes subjected to transient groundwater flow induced by reservoir drawdown conditions. Compared to that of porous media, the analysis of flow in fractured media is relatively complex, due to the presence of a large number of fractures and strong variations in geometric and hydraulic properties.The thesis is organized in six chapters. Chapter 1 presents the issues to be addressed and the thesis objectives. Chapter 2 discusses basic theories related to the numerical analysis of groundwater flow in fractured media and its effects on slope stability.Chapter 3 develops the numerical model of transient, saturated flow in fractured media with a free surface using the composite element method (CEM). Chapter 4 presents the numerical model of transient, variably-saturated flow in fractured media using the CEM.Chapter 5 includes an investigation of the stability of homogeneous soil slopes under drawdown conditions, depending on the drawdown rate, hydraulic and strength parameters of soils, and slope geometry.The last chapter presents a parametric study on the influence of fracture characteristics on transient flow and stability of layered rock slope subjected to drawdown conditions.