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 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.

This thesis is divided into two parts. The first one is focused on tracer tests carried out in several karst conduits in the Moravian Karst. Several conduits were tracer repeatedly during different discharges. Flow velocity, flow cross section area, longitudinal dispersivity and Peclet number were plotted against discharge for each studied conduit. Based on this comparison of parameters I deduced characteristics of karst conduits for example presence of phreatic channel or vadose channel or multiple channels. I also focused on comparison of my results with publications dealing with the same subject elsewhere in the world. Second part of the thesis is based on measurements of water stage, dischargeand temperature by pressure transducers at inlet and outlet points of karst conduit logged in 10 minutes interval. The goal was to find a relation between the velocity of hydraulic response propagation and discharge. Unfortunately, results show no correlation because there are probably more parameters influencing the velocity such as ratio of vadose/phreatic segments which may change rapidly during flood events.

Wastewater treatment plants (WWTPs) play a vital role in protecting the environment from much of the waste produced by humans. This includes not only human waste, but everything that makes its way into a sewerage system including greywater, stormwater, and potentially hazardous chemicals from, inter alia, chemical spills. The effects of a chemical spill if it enters a WWTP can be disastrous, resulting in the ineffective treatment of incoming water for prolonged periods of time (Söhr, 2014). This can lead to one of the dilemmas of urban wastewater systems, notably, whether it is more damaging to allow a chemical spill to bypass a WWTP, or to attempt to treat all or some of the spill and risk damaging the microbes working in the biological treatment processes (Schütze, 2002). In order to better inform policy makers and process engineers at WWTPs of which measures to take in the event of a spill, solute transport characteristics of a specific sewerage network must be defined.  A series of tracer tests were performed along The Käppala Association’s northern sewerage network to determine these solute transport characteristics, notably the dispersion coefficient which strongly affects the level of dilution that occurs between the injection point and the inlet. A simple solute transport model, carried out in Excel, was created using the Advection-Dispersion Equation (ADE) and the Manning-Strickler equation to relate flow measurements to flow velocity. Results from the experiments show that a dispersion coefficient of 1.55m2/s appears to be applicable throughout the whole of the tunnel network. A depth dependent Manning-Strickler coefficient seems to describe the flow-velocity relationship, however, this method has not been validated. The ADE begins to lose accuracy in describing solute transport as the distance from the inlet and the number of pumping stations the plume goes through increases. / Avloppsreningsverk spelar en viktig roll för att skydda miljön från mycket av det avfall som produceras av människor. Detta inkluderar inte bara mänskligt avfall utan allt som tar sig in i ett avloppssystem, till exempel gråvatten, dagvatten och potentiellt farliga kemikalier från bland annat industriutsläpp. Effekterna av ett kemiskt utsläpp kan vara katastrofala om det kommer in i ett avloppsreningsverk, vilket resulterar i ineffektiv behandling av inkommande vatten under längre perioder (Söhr, 2014). Detta är ett dilemma i urbana avloppssystem – ska man låta ett kemiskt utsläpp ledas förbi ett avloppsreningsverk, eller försöka behandla hela eller en del av utsläppet och riskera att skada mikroberna i den biologiska reningsprocessen (Schütze, 2002). För att beslutsfattare och processingenjörer vid avloppsreningsverk ska kunna fatta rätt beslut om vilka åtgärder som ska vidtas vid utsläpp måste egenskaperna för det specifika avloppsnätet definieras.  Syftet med detta projekt är att uppskatta transportparametrar och karakterisera utspädning i nätverket genom att utföra en serie spårningsförsök i Käppalaverkets upptagningsområde. För att nå syftet fanns det flera mål som genomförts: Genomföra en litteraturstudie  Skapa en förutsägbar modell i Excel baserad på flödesdata längs Käppalaförbundets tunnelsystem Genomföra en serie spårningsförsök vid flera punkter längs tunnelsystemet  Strukturerad datalagring av resultaten så att data är lätt att hitta för framtida projekt  Metoderna kan delas i två: modellering och försök. För att skapa en modell och simulera transport av ett ämne i nätet får man definiera relevanta ekvationer. För den hydrauliska delen av modellen användes Manning-Strickler-ekvationen. Resultaten från detta användes sedan i den förenklade formen av advektion-spridningsekvationen (ADE). Tunnelsystemet uppdelades i flera sektioner med samma egenskaper såsom form och geometri, och en anpassad form av ADE användes emellan sektionerna. För att nå framgång i försöken krävdes att rätt spårämne valdes. Uranin användes i försöken på grund av sina ogiftiga och stabila egenskaper och den låga detektionsgränsen. Injiceringspunkterna låg gradvis längre bort från inloppet; Försök 1 var 9km från verket till nästan 46km vid Arlanda flygplats för Försök 3.  Resultaten från simuleringarna användes för att planera injiceringstid, start- och stopptid för provtagningen och provtagningsfrekvens. Resultatet från första försöket användes för att kalibrera modellen inför de andra försöken. Resultaten från alla försök visade att en dispersionskoefficient på 1.55m2/s, som är ett mått på utspädning i nätet, verkar tillämpligt till hela tunnelsystemet. Koefficienten kan dock vara högre i de kommunala näten. En djupberoende metod för att härleda Mannings tal formulerades, men det kräver ytterligare validering.  Från alla tre försöken kan vi härleda ett förhållande mellan avstånd från inlopp och toppkoncentration samt avstånd från inlopp och varaktigheten av genombrottskurvan. Toppkoncentration visar ett linjärt eller kanske logaritmiskt förhållande med distans, och varaktigheten av genombrottskurvan visar ett starkt linjärt förhållande. Kunskaper om detta är viktigt när man vill genomföra en riskbedömning av ett kemiskt utsläpp i upptagningsområdet eftersom det ger en insikt om hur det kan påverka den biologiska reningen i ett avloppsreningsverk.  Sammanfattningsvis fungerar den enkla formen av ADE bra, men viss avvikelse ses i experiment 3. Detta beror kanske på möjliga övergående lagringsprocesser vid pumpstationerna längs tunnelsystemet. En enda dispersionskoefficient, som är ett mått på utspädning, är tillämplig i hela huvudtunnelsystemet, men spridningen i kommunala nätverk är sannolikt högre. Ytterligare arbete behövs inom dessa kommunala nätverk för att kvantifiera deras effekter.  På grundval av resultaten från detta projekt rekommenderas ytterligare forskningsundersökningar om vad som händer med föroreningar i avloppsreningsverket. Eftersom slammet vid Käppalaverket används för biogasproduktion och är Revaq-certifierat för användning på jordbruksmark är föroreningsnivån i slammet mycket viktigt både ur produktivitets- och hälso- och säkerhetsperspektiv.

Coal preparation plants are required in some cases to produce a high-grade product using a low specific gravity cut-point. For these situations, a second higher gravity separation would be desirable to generate a mid-grade product that can be utilized for electricity generation thereby maximizing coal recovery. A study was conducted to evaluate the potential of achieving efficient separations at two different density cut-points in a single stage using a three-product dense medium cyclone. Variations in density cut-point and process efficiency values were quantified as a function of the feed medium density, feed medium-to-coal ratio, and feed pressure using a three-level experimental design program. Results indicate the ability to effectively treat coal over a particle size range from 6mm to 0.15mm while achieving both low- and high-density cut-points up to 1.95 relative density. Ash content decreased from 27.98% in the feed to an average of 7.77% in the clean coal product and 25.76% in the middlings product while sulfur content was reduced from 3.87 to 2.83% in the clean coal product. The overall combustible recovery was maintained above 90% while producing clean coal products with ash and total sulfur content as low as 5.85 and 2.68%, respectively. Organic efficiency values were consistently about 95% and probable error values were in the range of 0.03 to 0.05, which indicates the ability to provide a separation performance equivalent to or better than traditional coal cleaning technologies.

Large depression cone in water table was formed due to mining in surroundings of Střeleč quarry. The concentrated inflow from conduits to quarry is up to 70 l/s. Large conduit systems are created by flowing water into the quarry. The biggest conduit system was at least 300 m long and 17 m high with maximum calculated volume of 22 thousands m3 . Evolution of these conduits usually takes several months to few years. Fast conduit evolution allows to study erosion processes in detail in situ. In the thesis I am describing conduits, character of flow and erosion processes. Measured flow velocities in conduits are up to 0,4 m/s with hydraulic gradient 1 to 5%. Flow velocities and hydraulic gradients are typical for piping erosion. Piping initially forms small protoconduits. The bigger conduits are formed as water is progressively drained from larger area. Conduits are following fracture surfaces, which are also limiting the conduit propagation to the sides. Above water table the conduits are enlarged mainly by mass wasting of undercut sandstone slabs. For distinguishing less and more erodible parts of sandstone, we adapted and partially developed a method for measuring erodability (REI) and drilling resistance (DR). Both are used to compare different types of sandstone surfaces. In lowermost part of the...

Reinjection of spent geothermal fluids has become common practise in geothermal power plants. Reinjection can, despite being mostly beneficial, have unwanted effects such as cooling of nearby production wells and injection-induced earthquakes. Tracer tests, along with their modeling and interpretation, are important tools for monitoring the flow paths of the injected water and to predict reservoir cooling. Knowledge of flow paths in the system allows for better resource management and a more sustainable utilization. A simulation model of the Húsmúli reinjection zone in the Hellisheiði Geothermal Power Plant in SW-Iceland was developed using the TOUGH2 program. Its hydrological parameters, porosity and permeability, were calibrated using results from an extensive tracer test carried out in the area in 2013-2015. The aim of the simulations was to obtain better understanding of the flow paths in Húsmúli since, despite fast tracer recovery in production wells in the area, hardly any cooling has been observed in those production wells. The results show that the tracer recovery can be modelled by means of permeable flow channels within the medium. Good results for tracer arrival and concentration peaks were obtained both by assuming a single wide channel and several narrower ones. The parameters that gave the best fit for the single channel model were permeability of 5·10-12 m2 and porosity ranging from 0.2%–3%. For the multi-channel model they were 1·10-12 m2 and 0.2%–3.5%, respectively. The high permeability and low porosity in the channels make for an abstract representation of fractured zones within the medium. Greater cooling was seen with the single-channel modelling approach than with the multiple narrower channel approach, the latter showing hardly any cooling in the production elements during the simulation time. This indicates that the flow paths are more likely multiple channels consisting of fracture networks. The simulations show that the flow paths are lengthened by sinking of the fluid to greater depth because of the higher density of the colder injected water. This implies that the injected fluid is warmed up by contact with a larger volume of rock, causing a limited and delayed cooling effect. / Geotermisk energi anses vara en förnybar och miljövänlig energikälla. Som sådan, kan den spela en viktig roll för att minska utsläppen av växthusgaser från energisektorn över hela världen och genom det bekämpa antropogena klimatförändringar. Geotermiska kraftverk extraherar het vätska från berggrunden, separerar ångan från vätskan och använder sedan ångan för att driva turbiner som genererar elektricitet. Injektion av använd geotermisk vätska från kraftverk har blivit vanligt i den geotermiska industrin för att kassera använd geotermisk vätska, upprätthålla systemtrycket och öka produktionseffektiviteten. Återinjektion av nedkyld vätska kan, trots att den är mestadels fördelaktig, ha oönskade effekter, såsom kylning av närliggande produktionsbrunnar och injektionsinducerad seismisk aktivitet. Spårprov, som möjliggör spårning av en kemikalie inom systemet, tillsammans med modellering, är viktiga verktyg för att förstå flödesvägarna för det injicerade vattnet samt att kunna förutsäga nedkylningar av vattenmagasin. Kunskap om flödesvägar i systemet möjliggör bättre resurshantering och ett mer hållbart användande. En simuleringsmodell av återinjektionszonen för det geotermiska kraftverket Hellisheiði på sydvästra Island, Húsmúli, utvecklades med hjälp av simuleringsprogrammet TOUGH2. Dess hydrologiska parametrar, permeabilitet och porositet, kalibrerades med hjälp av resultat från ett omfattande spårtest som utfördes i området 2013-2015. Syftet med simuleringarna var att få en bättre förståelse av flödesvägarna i Húsmúli. Detta er inressant eftersom trots en snabb återhämtning av spårämne i produktionsbrunnar, har knappt någon kylning observerats i området. Resultaten visar att återhämtningen av spårämnet inte kan modelleras med ett homogent medium, men kan istället modelleras genom att bygga permeabla strömningskanaler inom mediet. Goda resultat för spårämnesankomst och koncentrationstoppar erhölls både genom att använda en enda bred kanal och flera smalare. Kanalerna ger en abstrakt representation av sprickzoner inom mediet. Större kylning observerades för modelleringsmetoden med en enkel bred kanal än med flera smalare kanaler. Detta indikerar att flödesvägarna i området troligtvis går genom flera sprickzoner. Flödesvägarna förlängs genom att vätskan sjunker till ett större djup på grund av den högre densiteten hos det injicerade vattnet. Detta innebär att den injicerade vätskan värms upp genom kontakt med en större volym berg, vilket medför en begränsad och fördröjd kylningseffekt.

Dans les systèmes d’Electrolyse Haute Température (EHT), le matériau choisi comme interconnecteur doit avoir une bonne résistance à la corrosion sous air et sous mélange H2/H2O à 800 °C, et maintenir une bonne conductivité sur de longues durées. Dans ce cadre, l’objectif de ce travail était, d’une part, d’évaluer un alliage ferritique commercial (l’alliage K41X) comme matériau d’interconnecteur pour l’application EHT. Dans ce but, ont été mis en place des essais d’oxydation en four et en thermoblance pour accéder aux cinétiques d’oxydation, et des mesures de résistivité pour évaluer le paramètre ASR (Area Specific Resistance) à 800°C. D’autre part, l’étude a permis d’apporter des éléments de compréhension plus fondamentaux sur les mécanismes d’oxydation des alliages chromino-formeurs, en particulier sous mélange H2-H2O, par le biais d’essais et de caractérisations spécifiques (Photoélectrochimie, traçage isotopique, essais de longues durées). Cette double stratégie est également appliquée pour l’étude d’une solution de revêtement (obtenu à l’aide de la MOCVD) basée sur l’oxyde pérovskite LaCrO3 qui présente des propriétés de conductivité élevée particulièrement intéressante en vue de l’application EHT. Ainsi, cette étude amène également des éléments de compréhension sur le rôle du lanthane comme élément réactif dont l’effet est souvent discuté dans la littérature. Pour les deux milieux, à 800°C, la couche d’oxyde formée est une couche duplexe Cr2O3/(Mn,Cr)3O4 , recouverte dans le cas du mélange H2-H2O par une fine couche d’oxyde spinelle Mn2TiO4 . Sous air, le mécanisme de croissance déterminé ici est cationique, en accord avec la littérature. La présence d’un revêtement LaCrO3 ne modifie pas ce mécanisme mais ralentit la cinétique de croissance de la couche sur les premières centaines d’heure. De plus, le revêtement améliore l’adhérence et la conductivité de la couche d’oxyde. Sous mélange H2-H2O, le mécanisme de croissance se révèle anionique. La présence de revêtement ralentit la cinétique d’oxydation. Bien que .d’épaisseurs similaires, les couches d’oxyde présentent sous air une résistivité d’un ordre de grandeur inférieure à celle mesurée sous H2-H2O. Il est mis en évidence que la forte résistivité de l’alliage en milieu H2-H2O est liée à la présence de protons issus de la vapeur d’eau présents dans la couche d’oxyde. Le revêtement ne permet néanmoins pas d améliorer la conductivité sous H2-H2O. / In High Temperature Vapor Electrolysis (HTVE) system, the materials chosen for the interconnectors should have a good corrosion behaviour in air and in H2-H2O mixtures at 800°C, and keep a high electronic conductivity over long durations as well. In this context, the first goal of this study was to evaluate a commercial ferritic alloy (the K41X alloy) as interconnect for HTVE application. Oxidation tests in furnace and in microbalance have therefore been carried out in order to determine oxidation kinetics. Meanwhile, the Area Specific Resistance (ASR) was evaluated by Contact Resistance measurements performed at 800°C. The second objective was to improve our comprehension of chromia-forming alloys oxidation mechanism, in particular in H2/H2O mixtures. For that purpose, some specific tests have been conducted: tracer experiments, coupled with the characterization of the oxide scale by PEC (PhotoElectroChemistry). This approach has also been applied to the study of a LaCrO3 perovskite oxide coating on the K41X alloy. This phase is indeed of high interest for HTVE applications due to its high conductivity properties. This latter study leads to further understanding on the role of lanthanum as reactive element, which effect is still under discussion in literature.In both media at 800°C, the scale is composed of a Cr2O3/(Mn,Cr)3O4 duplex scale, covered in the case of H2-H2O mixture by a thin scale made of Mn2TiO4 spinel. In air, the growth mechanism is found to be cationic, in agreement with literature. The LaCrO3 coating does not modify the direction of scale growth but lowers the growth kinetics during the first hundreds hours. Moreover, with the coating, the scale adherence is favored and the conductivity appears to be slightly higher. In the H2-H2O mixture, the growth mechanism is found to be anionic. The LaCrO3 coating diminishes the oxidation kinetics. Although the scale thickness is about the same in both media, the ASR parameter is one order of magnitude higher in H2/H2O than in air. Specific contact resistance tests show that the higher resistivity in the H2/H2O mixture is closely linked to the presence of protons in the scale. Moreover, tracer experiments show that these protons come from the water molecule dissociation, and not from the H2 molecule. In H2/H2O, the LaCrO3 coating does not increase the conductivity

In addition to a loss of potential revenues from Utah's $393 million sport fishing industry, the state expends millions of dollars every year on costs associated with whirling disease mitigation and prevention. A state fish hatchery at Midway, Utah was closed when the shallow unconfined aquifer being used for fish culture by spring discharge was deemed to be contaminated by whirling disease. An alternative water source may exist in a confined aquifer below this contaminated unconfined aquifer. However, the complex hydrostratigraphy presents a challenge in determining if this source is a viable resource for fish culture. Geological, physical, chemical, geophysical, and isotopic data were combined to create a conceptual model of the groundwater flow at the site and to determine the interactions this confined aquifer may have with the contaminated aquifer. This model divides groundwater at the hatchery into a shallow unconfined system, an upper confined system, and a lower confined system. The shallow unconfined system is characterized by a water table ~1m below ground surface, several active springs, fast travel times, modern water mixed with ancient hydrothermal water, relatively high TDS, and relatively enriched isotopic values. The confined aquifers have a smaller hydrothermal component, relatively depleted isotopic values, lower TDS, and modern recharge components. Two orthogonal shallow high-resolution seismic reflection profiles indicate substantial heterogeneity in the subsurface at the level of the confined systems at the hatchery. Several north-south trending normal discontinuities were interpreted as possible faults from the seismic profile oriented as a dip line, whereas the strike profile shows discontinuous layering without noticeable faulting. A well log profile for the site shows discontinuous tufa layers amid heterogeneous alluvium material. These tufa layers separate upward leaking confined aquifers from the unconfined system. It is only through the integration of several methods that such mixed systems, can be understood. In this study, the lower confined aquifer was found to be a sufficient and safe resource through the integration of numerous methods.

ABSTRACT In the first part of this study, a determinist mathematical approach is used to describe any kind of pollutant migration in groundwater. This theoretical background is focused on the miscible displacement and the particularities of the multiporous media are discussed. Subsequently, an objective numerical tool is developed to solve the convection-dispersion equations including immobile water effect, degradation, and adsoption. Among all the available techniques, two finite element methods in fixed meshing grids have been programmed: -the F.U.P.G. method (Full Upwind Petrov Galerkin), using a space-time upwinded weighting function with optimized coefficients, -the H.E.L.M. method (Hybrid Eulerian Lagrangian Method), using the eulerian lagrangian approach with reverse node tracking. Those two schemes are tested on a large number of reference problems. The model have been applied to study the behaviour of solutes (nitrates mainly) in the cretaceous chalk of the Hesbaye area (Belgium). Experimentations have been performed on domains of increasing size (laboratory tests, in situ tracer tests). For each interpretation, the particularities of the context have been taken into account, and miscible transport coefficients have been objectively determined. Hence, the medium is well characterized and the scale effect is quantified. This leads to previsional applications. RESUME Ce travail débute par le développement dun formalisme mathématique déterministe pour décrire, en toute généralité, la propagation de polluants dans les eaux souterraines. Cette étude théorique permet de situer le problème posé (pollution miscible diluée) dans un cadre plus large, et de souligner les particularités dun milieu à porosité multiple. Dans un second temps, un outil numérique objectif est mis au point pour résoudre les équations de convection-dispersion avec effet deau immobile, dégradation, et adsorption. Parmi le grand nombre des procédés existants, deux méthodes par éléments finis en maillage fixe ont été programmées : -la méthode F.U.P.G. (Full Upwind Petrov Galerkin) basée sur un décentrage des fonctions de pondération, optimum dans le temps et lespace, -la méthode H.E.L.M. (Hybrid Eulerian Lagrangian Method) utilisant un processus eulerien lagrangian avec traçage inverse des positions nodales. Les deux schémas sont testés sur de nombreux problèmes de référence. Ensuite, ce modèle est appliqué à des situations pratiques pour étudier le comportement de solutés (nitrates notamment) dans laquifère crayeux du Crétacé de Hesbaye (Belgique). Des domaines de taille croissante sont étudiés (essais de laboratoire, traçage in situ). A chaque étape, les coefficients de transport miscible sont déterminés de façon objective, en tenant compte de la spécificité des tests. Ainsi, leffet déchelle peut être quantifié et il est possible denvisager des scénarios prévisionnels.