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1
Vlatsa, Dimitra A. « Stochastic control of groundwater systems ». Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/19426.
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Pérez, Paricio Alfredo. « Integrated modelling of clogging processes in artificial groundwater recharge ». Doctoral thesis, Universitat Politècnica de Catalunya, 2001. http://hdl.handle.net/10803/6214.
Texte intégralRésumé :
La Recàrrega Artificial d'aqüífers és una tècnica extremadamente poderosa per optimitzar la gestió dels recursos hídrics. De cara a eliminar actituds escèptiques respecte a la seva aplicabilitat en nombroses situacions, és essencial adquirir més coneixements sobre els conceptes quantitatius més importants. Un tema crític és el de la minimització de la colmatació en dispositius de recàrrega. Atesa la extraòrdinaria importància d'aquest problema, es va efectuar una intensa recerca bibliogràfica que permetés determinar els processos bàsics que tenen lloc en la colmatació de plantes de recàrrega. Això, juntament amb la informació de tipus tecnológic subministrada per gestors de plantes de recàrrega, ha permès proposar un model matemàtic conceptual que integra els processos principals: retenció de partícules en suspensió portades per l'aigua de recàrrega, precipitació de minerals, creixement bacterià, generació de gas y compactació. Amb l'ajuda dels codis ja existents, l'esmentat model fou posteriorment incorporat a un programa d'elements finits tridimensionals que és capaç de tractar els cinc processos citats. El programa ha estat aplicat a tres casos de laboratori i a un experiment de camp amb el fi d'establir la validesa del marc conceptual adoptat.Aquesta tesi descriu els aspectes principals del model, els seus fonaments teòrics, la implementació numèrica i l'aplicació als exemples citats. La varietat de condicions simulades i els resultats aconseguits confirmen que el programa pot reproduir de forma satisfactòria una ampli ventall de problemes de colmatació, entre les quals s'inclouen sistemes superficials (bassas) i profunds (pous), flux radial i vertical, transport reactiu multicomponent, i d'altres. Això demostra la utilitat del programa per integrar dades de naturalesa completament diferente. A pesar de les limitacions inherents a tota formulació matemàtica, la modelació integrada proporciona estimacions quantitatives del potencial colmatant. Consegüentment, pot ser considerada com a una eina bàsica per al disseny i gestió de plantes de recàrrega i, eventualment, amb un fi predictiu.
La Recarga Artificial de acuíferos es una técnica extremadamente poderosa para optimizar la gestión de los recursos hídricos. De cara a eliminar actitudes escépticas respecto a su aplicabilidad en numerosas situaciones, es esencial adquirir más conocimientos sobre los conceptos cuantitativos más importantes. Un tema crítico es el de la minimización de la colmatación en dispositivos de recarga. Dada la extraordinaria importancia de este problema, se efectuó una intensa búsqueda bibliográfica que permitiera determinar los procesos básicos que tienen lugar en la colmatación de plantas de recarga. Esto, junto con la información de tipo tecnológico suministrada por gestores de plantas de recarga, ha permitido proponer un modelo matemático conceptual que integra los procesos principales: retención de partículas en suspensión en el agua de recarga, precipitación de minerales, crecimiento bacteriano, generación de gas y compactación. Con la ayuda de códigos ya existentes, dicho modelo fue posteriormente incorporado en un programa de elementos finitos tridimensional que es capaz de tratar los cinco procesos citados. El programa ha sido aplicado a tres casos de laboratorio y a un experimento de campo con el fin de establecer la validez del marco conceptual adoptado.
Esta tesis describe los aspectos principales del modelo, sus fundamentos teóricos, la implementación numérica y la aplicación a los ejemplos citados. La variedad de condiciones simuladas y los resultados logrados confirman que el programa puede reproducir de forma satisfactoria una amplia gama de problemas de colmatación, entre las que se incluyen sistemas superficiales (balsas) y profundos (pozos), flujo radial y vertical, transporte reactivo multicomponente, y otros. Esto demuestra la utilidad del programa para integrar datos de naturaleza completamente diferente. A pesar de las limitaciones inherentes a toda formulación matemática, la modelación integrada proporciona estimaciones cuantitativas del potencial colmatante. Por consiguiente, puede ser considerada como una herramienta básica de cara al diseño y gestión de plantas de recarga y, eventualmente, de cara a la predicción.
Artificial Recharge of groundwater is an extremely powerful technique to optimise the management of water resources. In order to eliminate sceptical misconceptions concerning its applicability to numerous situations, it is essential to gain insight into the fundamental quantitative concepts. A critical point is the minimisation of clogging of the recharge device. Given the extraordinary importance of this problem, an intensive bibliographic research was conducted to determine the basic processes underlying the clogging of recharge plants. This, in combination with technological information supplied by Artificial Recharge operators, allowed to propose a conceptual mathematical model that could integrate the main processes. Attachment of suspended solids carried by recharge water, mineral precipitation, bacterial growth, gas binding and compaction of the upper soil layer were found to be determinant in clogging development. Based on existing investigation codes, such model was implemented into a three-dimensional finite element code that is able to cope with the referred mechanisms. The code was applied to three laboratory cases and to one field experiment in order to assess the validity of the adopted framework.
This thesis includes the main concepts of the model, its theoretical background, numerical implementation and the application to the referred cases. The variety of simulated conditions and the results achieved with the model confirm that the code can reproduce successfully a wide range of clogging problems, including surface (basins) and deep (wells) systems, vertical and radial flow, multiphase transport and other options. This demonstrates the usefulness of the code to integrate data which are completely different in nature. In spite of the limitations inherent to all mathematical formulations, integrated modelling provides quantitative estimates of the clogging potential. Consequently, can be considered as a basic tool for design and management of recharge plants, and, eventually, for predictive purposes.
3
Bockgård, Niclas. « Groundwater Recharge in Crystalline Bedrock : Processes, Estimation, and Modelling ». Doctoral thesis, Uppsala University, Department of Earth Sciences, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4573.
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Kunskap om grundvattenbildningen är nödvändig för att man ska kunna förutsäga konsekvenserna av grundvattenuttag och underjordsbyggande. Grundvattenbildningen i berggrunden är dock svår att uppskatta. Syftet med avhandlingen var att öka förståelsen av grundvattenbildningen i kristallin berggrund, att undersöka hur grundvattenbildningen ska uppskattas samt att utveckla nya modeller för att beskriva grundvattenbildningen. Studien grundades på tre angreppssätt: grundvattendatering med freoner (CFC), geohydrauliska observationer och matematisk modellering.
Koncentrationerna av CFC-11 och CFC-113 befanns vara låga i det undersökta berggrundvattnet, vilket i kombination med låga syrgashalter tyder på anaerob nedbrytning. Koncentrationerna av CFC-12 och tritium överensstämde ganska väl, vilket betyder att den skenbara åldern kan vara den sanna åldern. Resultaten tyder på att CFC-datering inte är pålitlig i skogsmiljöer med finkornigt jordtäcke.
Vid nederbörd observerades ett snabbt gensvar i den hydrauliska potentialen i den studerade bergakviferen, trots det 10 m mäktiga moräntäcket. En avsevärd del av de observerade potentialvariationerna befanns vara belastningseffekter, som inte innebar någon magasinsförändring eller något vattenflöde. Berggrundens belastningseffektivitet uppskattades, ur potentialens svar på lufttrycksförändringar, till 0,95. Ytbelastningen beräknades från mätningar av lufttryck, vatten i jordtäcket och snö. Omkring 20 % av årstidsvariationen hos den hydrauliska potentialen uppskattades bero på enbart belastningsförändringar. En enkel begreppsmässig modell kunde användas för att simulera den observerade hydrauliska potentialen. För att beskriva enskilda grundvattenbildningstillfällen på bästa sätt var det nödvändigt att ta hänsyn till effekten av ytbelastningen.
Numeriska experiment gjordes med en modell av en jord–bergprofil. När berget modellerades som ett heterogent kontinuum bildades omättade zoner i berget vid stora hydrauliska gradienter. Fenomenet uppträdde i områden där låggenomsläppliga zoner låg uppströms höggenomsläppliga zoner, och ledde till minskad hydraulisk konduktivitet i berget.
Knowledge about the groundwater recharge is essential for the prediction of impacts of groundwater withdrawal and underground construction. Recharge in the bedrock is, however, difficult to estimate. The objectives of this thesis were to increase the understanding of groundwater recharge in crystalline bedrock, to investigate how the recharge could be estimated, and to develop new models to describe the recharge. The study was based on three approaches: groundwater dating using chlorofluorocarbons (CFCs), geohydraulic field measurements, and mathematical modelling.
Low concentrations of CFC-11 and CFC-113 were found in the bedrock groundwater, which in combination with low dissolved-oxygen levels indicated anaerobe degradation. The CFC-12 and tritium concentrations agreed fairly well, which means that apparent ages could be true ages. The results suggest that CFC dating may not be reliable at forested, humid sites covered by fine-grained soil.
A quick response in hydraulic head to precipitation was observed in the studied bedrock, despite the 10-m thick till cover. A substantial portion of observed head variations was found to be loading effects, involving no storage changes or water flow. The loading efficiency of the bedrock was estimated, from the air-pressure response, to be 0.95. The surface loading was calculated from measurements of air pressure, water in the soil, and snow. About 20% of the seasonal variation of the hydraulic head was estimated to be related to loading changes only. A simple conceptual model could be used to simulate the observed hydraulic heads. The loading effect had to be included to properly describe individual recharge events.
Numerical experiments were performed with a soil–bedrock profile. When the rock was modelled as a heterogeneous continuum, unsaturated zones developed at high hydraulic gradients. The phenomenon appeared in areas where low-conductive zones were located upstream of high-conductive zones, decreasing the effective hydraulic conductivity of the material.
4
Xaza, Abongile. « Investigating hydrogeochemical processes of groundwater, Heuningnes Catchment, South Africa ». University of the Western Cape, 2020. http://hdl.handle.net/11394/7961.
Texte intégralRésumé :
Masters of ScienceThis study was conducted to investigate hydrogeochemical processes controlling the evolution of groundwater chemistry and their influence on water quality in the Heuningnes Catchment. The role or influence of hydrogeochemical processes in groundwater quality in aquifer systems remains poorly understood. One of the ways of improving such understanding is to employ different techniques to explore key processes that govern groundwater quality in aquifer systems. Therefore, the present study investigated hydrogeochemical processes of groundwater resources and identified key processes that explained its quality from a spatiotemporal perspective. The quantitative approach that provides the ability to assess relationships between variables both spatially and temporally was applied. Groundwater sampling was done on four occasions during July 2017, October 2017, March 2018, and July 2018. Identification of hydrogeochemical processes controlling the evolution of groundwater chemistry and quality was done using various complementary tools. These tools included classification of the main water types, evaluation of water-rock interaction by means of stoichiometry analysis and bivariate correlation plots, inverse geochemical modelling, and statistical analysis (hierarchical cluster analysis and factor analysis). Physical parameters were measured in situ, while water samples were collected from boreholes, piezometers, springs, and artesian boreholes for laboratory analysis for major ions analysis. Descriptive and bivariate statistical methods were used to summarise and evaluate the strength of the relationship between variables, while multivariate statistical methods were applied to group similar samples based on their chemical compositions. Tri linear Piper diagrams were generated to characterize water type based on double normalizing the proportions of cations and anions, while correlation and stoichiometric analysis were applied to identify hydrogeochemical processes influencing groundwater chemistry. The results generated from the trilinear Piper diagrams confirmed the dominance of sodium and chloride ions in waters of the Heuningnes Catchment. Groundwater of a Na/Cl type is typical for a coastal aquifer characterised by saline, deep ancient groundwater. The lower parts of the Catchment were characterised by saline groundwater. The results indicated that shallow groundwater samples within the study area were more mineralised as compared to deep groundwater with EC values ranging between 20.8 and 2990 mS/m, with waters within the Table Mountain Group region (TMG), recording the lowest values. Deep groundwater for boreholes and artesian boreholes located upstream in the Catchment was fresh and yielded some of the lowest EC values recorded with an EC value below 50 mS/m. Generally, EC values increased from the upper TMG region of the Catchment towards the Bokkeveld shale region downstream and were highest during the dry season of 2018. The results indicated strong geological influences on water chemistry. Bivariate correlation and stoichiometric analysis identified cation exchange, adsorption, evaporation, weathering of carbonates, sulphates and silicate minerals as processes influencing the chemistry of groundwater in the Heuningnes Catchment. The Saturation Index (SI) results showed a change of calcite, dolomite, aragonite, gypsum, anhydrite, halite, melantinterite, siderite and sylvite from being undersaturated to oversaturated at some areas for the different seasons along the flow path. The mass-balance modelling results indicated that ion exchange and reverse ion exchange processes were more dominant at low elevations along the same flow path during the dry periods. However, at high elevations along the flow path, silicate weathering was the dominant process taking place. The findings of this study demonstrated the influence of hydrogeochemical processes in changing the water chemistry along the flow paths. In conclusion, the study showed the value of utilising various assessment tools as complementary techniques to improve the understanding about hydrogeochemical processes, and its influence on evolution of groundwater chemistry and quality. Based on the findings of the study the following recommendations were made for future studies; the sample points or sample boreholes in the study Catchment should be increased; and to have more sampling trips to enable better comparison between the possible processes
5
Ciriello, Valentina <1983>. « Model reduction of stochastic groundwater flow and transport processes ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5937/1/ciriello_valentina_tesi.pdf.
Texte intégralRésumé :
This work presents a comprehensive methodology for the reduction of analytical or numerical stochastic models characterized by uncertain input parameters or boundary conditions. The technique, based on the Polynomial Chaos Expansion (PCE) theory, represents a versatile solution to solve direct or inverse problems related to propagation of uncertainty. The potentiality of the methodology is assessed investigating different applicative contexts related to groundwater flow and transport scenarios, such as global sensitivity analysis, risk analysis and model calibration. This is achieved by implementing a numerical code, developed in the MATLAB environment, presented here in its main features and tested with literature examples. The procedure has been conceived under flexibility and efficiency criteria in order to ensure its adaptability to different fields of engineering; it has been applied to different case studies related to flow and transport in porous media. Each application is associated with innovative elements such as (i) new analytical formulations describing motion and displacement of non-Newtonian fluids in porous media, (ii) application of global sensitivity analysis to a high-complexity numerical model inspired by a real case of risk of radionuclide migration in the subsurface environment, and (iii) development of a novel sensitivity-based strategy for parameter calibration and experiment design in laboratory scale tracer transport.
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Ciriello, Valentina <1983>. « Model reduction of stochastic groundwater flow and transport processes ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5937/.
Texte intégralRésumé :
This work presents a comprehensive methodology for the reduction of analytical or numerical stochastic models characterized by uncertain input parameters or boundary conditions. The technique, based on the Polynomial Chaos Expansion (PCE) theory, represents a versatile solution to solve direct or inverse problems related to propagation of uncertainty. The potentiality of the methodology is assessed investigating different applicative contexts related to groundwater flow and transport scenarios, such as global sensitivity analysis, risk analysis and model calibration. This is achieved by implementing a numerical code, developed in the MATLAB environment, presented here in its main features and tested with literature examples. The procedure has been conceived under flexibility and efficiency criteria in order to ensure its adaptability to different fields of engineering; it has been applied to different case studies related to flow and transport in porous media. Each application is associated with innovative elements such as (i) new analytical formulations describing motion and displacement of non-Newtonian fluids in porous media, (ii) application of global sensitivity analysis to a high-complexity numerical model inspired by a real case of risk of radionuclide migration in the subsurface environment, and (iii) development of a novel sensitivity-based strategy for parameter calibration and experiment design in laboratory scale tracer transport.
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Taylor, Sarah Leanne. « The hydrogeochemistry of shallow groundwater in Western Sydney : a study of salinisation processes in shallow groundwater ». Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/16115.
Texte intégralRésumé :
Groundwater salinity is widespread in Western Sydney; however, little is known about the processes which cause it. This thesis explored many features of the shallow groundwater system using a range of hydrogeological, geochemical and statistical techniques. Geostatistical analysis of historical data highlighted that 53.6% of the study region had shallow groundwater with an electrical conductivity exceeding 2,000µS/cm. Salinisation hazard mapping indicated that 0.66% of the region has a high salinisation hazard and 54.2% has a moderate salinisation hazard. The high-temporal-resolution dataset collected for this study, allowed the recharge and salt source (modern rainfall) to be identified, plus mechanisms of salt accumulation (cyclic process of evaporation and re-dissolution driven by high rates of evapotranspiration and clay-rich soils), and transport. From this, a geochemical model identifying the processes contributing to groundwater salinisation, and a conceptual model of the hydrogeological system were developed. Multivariate analysis identified seven water-types, their geographical distribution, and the causes of temporal variability for each water-type. Saline groundwater was found in many parts of the landscape, though temporal variability was generally limited. The monthly comparison approach, which analyses temporal variability, was developed for this study. This method increased our understanding of system variability and its causes, ultimately improving the conceptual model. The conceptual model generalises the geographical distribution of water-types based on landscape features, while temporal variability is related to water-types. The model significantly improves our understanding of the groundwater system, and our ability to manage it. Additionally, this study has illustrated that groundwater salinity arising from evaporative processes could be more wide-spread than currently thought, and may not be confined to arid or semi-arid environments.
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Hensley, Patricia Jane. « Accelerated physical modelling of transport processes in soil ». Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292742.
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Austin, Martin J. « Swash, groundwater and sediment transport processes on a gravel beach ». Thesis, Loughborough University, 2005. https://dspace.lboro.ac.uk/2134/34493.
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The morphodynamics of a steeply sloping gravel beach in the south western UK (tanβ = 0.15–0.2; d50 = 6 mm; ξb = 1–4) were measured during low energy wind-wave conditions (Hb < 0.5 m). Measurements of water depth, groundwater-level, waves and currents, concurrent with observations of morphological change and swash sediment loads, were successfully obtained over two spring-to-neap tidal cycles and used to investigate the short-term evolution of gravel beach morphology. Incident frequency motions dominated the hydrodynamics since wave transformation was concentrated at the base of the beach. Subharmonic energy was of secondary importance at most, never exceeding 15% of the total energy. Standing edge waves were generally absent since the lack of swell waves limited their forcing, and there was c. 50% reflection of the gravity-band energy.
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Petersen, Robin Marc. « A conceptual understanding of groundwater recharge processes and surface-water/ groundwater interactions in the Kruger National Park ». Thesis, University of the Western Cape, 2012. http://hdl.handle.net/11394/5204.
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>Magister Scientiae - MScIn the Kruger National Park (KNP) which is the flagship conservation area in South Africa, the impact on groundwater should be kept to a minimum as groundwater plays a vital role in sustaining ecosystem functioning and sustaining baseflow to streams and rivers. For this reason groundwater has been recognized as one of the environmental indicators that need to be monitored. The KNP has adopted a Strategic Adaptive Management (SAM) approach with clear ecosystem management goals. The achievement of these goals is evaluated by using environmental indicators. These indicators are evaluated against thresholds of potential concern (TPC). TPCs are a set of boundaries that together define the spatiotemporal conditions for which the KNP ecosystem is managed. TPCs are essentially upper and lower limits along a continuum of change in selected environmental indicators. Historically, groundwater recharge and surface water interaction with rivers has tended to be overlooked in the KNP. This study proposes a conceptual model of groundwater recharge processes in the KNP, defining when and how groundwater recharge occurs. Two methods were used, the Cumulative Rainfall Departure (CRD) and stable isotopes of ²H and ¹⁸O. An adapted version of the CRD which incorporates a long and short term memory of the system was used to identify possible recharge processes. Further, using the CRD method a reliable reconstruction of the long term groundwater level trends are simulated using monthly rainfall totals with reference to the average rainfall over the entire time series 1936-2009. The stable isotope of ²H and ¹⁸O samples from cumulative rainfall samplers, surfacewater (streams and rivers) and groundwater from boreholes were collected monthly for approximately one year (May 2010 to July 2011). The isotope composition of the groundwater was used to establish whether recharge was immediate or delayed. Additionally, the isotopic composition of surface-water from rivers and streams were compared to that of groundwater to identify surface-water interactions. Groundwater recharge in KNP occurs during the rainy summer months (December to March) and very little to none during the dry winter season (April to September). Recharge takes place during rainfall sequences 100mm or more. The stable isotope records collected from cumulative rainfall, groundwater and surface water (streams and rivers) indicate that groundwater experiences evaporation prior to infiltration. As the KNP experiences high evaporation rates, insignificant rainfall sequences contribute little or zero to recharge. The CRD analysis of groundwater level fluctuations shows that recharge to the aquifers respond to dry and wet cycles that last for 6 to 14 years. The KNP experienced several periods of below-average rainfall and hence no significant recharge took place to the basement aquifers. During a normal rainy season the water levels rise somewhat then starts receding again. It is only during major rainfall events that may occur every 100yrs to 200yrs causing the aquifers to fully recharge. This was perfectly illustrated by the high groundwater levels after the 2000 major rainfall event that recharged the aquifers fully. During below average rainfall years the overall water level trend is drastically declining. The system experiences higher natural losses than gains due to outflow of groundwater to streams and rivers. The KNP is divided down the center by two geological formations, granites along the west and basalts along the east. The combination of the CRD model and the stable isotopic analysis suggest that the dominant recharge processes that occur in the southern region of the KNP are direct recharge via piston flow and indirect recharge via preferred pathways particularly streams and rivers. Along the eastern half of the KNP on the Basalts and Rhyolite direct recharge via piston flow are dominant. Groundwater is not recharged via small streams and rivers (Sweni and Mnondozi Rivers) as it was found that at these particular sites these rivers are detached and do not interact with groundwater. Along the western granitic areas the dominant recharge process are indirect recharge. Recharge takes place via preferred pathways particularly streams and rivers. It was found that ephemeral rivers (Nwatsisonto River) act as sinks for groundwater recharge and influent-effluent conditions are experienced along seasonal rivers (Mbyamiti River). The large perennial Sabie and its tributary the Sand River are consistently fed by groundwater, above all maintaining base flow during the dry season. These rivers act as basin sinks receiving groundwater discharge all year round. Using the stable isotope composition of rainfall, surface-water and groundwater to act as a natural tracer, in combination with the CRD method proved invaluable to confirm the plausible recharge processes. The study provided a conceptual understanding of the groundwater system in the KNP forming the foundation to developing acceptable limits (TPCs) of the groundwater levels in the KNP. The model will serve as a guide for the recharge processes and for deciding on the location and time frames for data collection to ultimately set TPCs for groundwater in the KNP to sustainably manage the resource.
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Schilling, Keith Edwin Zhang You-Kuan. « Hydrological processes inferred from water table fluctuations, Walnut Creek, Iowa ». [Iowa City, Iowa] : University of Iowa, 2009. http://ir.uiowa.edu/etd/430.
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Richardson, Grant Vincent. « Processes affecting the attenuation of leachate within the attenuation landfill environment ». Thesis, University of Newcastle Upon Tyne, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322161.
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Wolf, Leah Michelle. « A field study of non-reactive transport behavior and evaluation of diffusion mediated processes ». Thesis, The University of Arizona, 2003. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_etd_hy0264_sip1_w.pdf&type=application/pdf.
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Calderer, Perich Montserrat. « Study of Denitrification and Reductive Dechlorination Processes Applied to Groundwater Bioremediation ». Doctoral thesis, Universitat Politècnica de Catalunya, 2010. http://hdl.handle.net/10803/6996.
Texte intégralRésumé :
La present tesi es basa en l'estudi dels processos de bioremediació com a tecnologies de descontaminació d'aqüífers.Concretament, es pretén estudiar la desnitrificació i la decloració reductiva com a tecnologies de bioremediació per eliminar, respectivament, els nitrats i els hidrocarburs alifàtics clorats (o CAHs, de chlorinated aliphatic hydrocarbons) de les aigües subterrànies contaminades. A més, es pretén aplicar tecnologies avançades que permetin millorar en el coneixement d'aquests processos.
L'aqüífer associat a la riera d'Argentona, situat a Argentona (Espanya), ha estat la zona d'estudi per tal d'investigar el procés de desnitrificació. En primer lloc, s'han dut a terme experiments en batch amb aigua subterrània i sòl subsuperficial del mencionat aqüífer. A partir d'aquests primers estudis, s'ha observat la baixa capacitat de l'aqüífer per eliminar els nitrats de manera natural, però alhora s'ha vist la viabilitat d'aplicar un procés de bioremediació com és l'addició de matèria orgànica. Paral·lelament, s'ha estudiat la influència de diferents factors com ara la presència d'oxigen i la tipologia de donador d'electrons sobre el procés de desnitrificació.
Posteriorment, s'ha desenvolupat un model matemàtic per descriure el consum d'oxigen, de nitrats i de matèria orgànica per part de la població microbiana facultativa i heterotròfica present en el material d'aqüífer. Alguns paràmetres del model han estat calibrats i s'ha estudiat la qualitat d'aquests paràmetres. El model desenvolupat constitueix una primera aproximació per tal d'obtenir un model de desnitrificació in situ.
Per tal d'avançar en l'estudi del procés de desnitrificació en condicions naturals, s'han realitzat experiments en dinàmic simulant el flux d'aigua subterrània a través de l'aqüífer. L'eficiència d'injectar matèria orgànica en aquestes condicions s'ha demostrat.
Paral·lelament, s'han estudiat els efectes hidrodinàmics de l'aplicació de la bioremediació i, els resultats han demostrat la importància de dissenyar acuradament les tecnologies de bioremediació a escala de camp. Per altra banda, s'ha descrit la desnitrificació en condicions dinàmiques integrant en un model matemàtic les reaccions bioquímiques i els processos de transport que tenen lloc a la columna experimental.
Finalment, s'han aplicat les noves tecnologies de biologia molecular per entendre els efectes de l'aplicació d'un procés de bioremediació a nivell microbià. Per una banda, l'aplicació de la tècnica de la reacció en cadena de la polimerasa a temps real (o real-time PCR, de real-time polymerase chain reaction) ha demostrat el creixement de la població microbiana i, concretament, de la població desnitrificant en el material d'aqüífer estimulat. Per altra banda, l'electroforesi en gel de gradient desnaturalitzant (o DGGE, de denaturing gradient gel electrophoresis) ha permès investigar els canvis en la població microbiana indígena del material d'aqüífer a causa de l'estimulació amb matèria orgànica.
Amb l'objectiu d'avançar en el coneixement dels processos de bioremediació en aigües subterrànies, s'ha estudiat també la decloració reductiva de CAHs. En aquest cas, s'han aplicat metodologies experimentals destinades a l'estudi de la posible aplicació d'una barrera reactiva permeable per eliminar una ploma que conté majoritàriament cis-1,2-dicloroetilè i clorur de vinil, i que flueix cap al riu Zenne, prop de la ciutat de Brussel·les (Bèlgica).
L'estudi ha inclòs experiments en batch per tal d'investigar el potencial degradatiu del material d'aqüífer i dels propis sediments del riu Zenne. Així mateix, també s'han dut a terme experiments en columna que simulaven el flux d'aigua subterrània a través dels sediments del riu o del material d'aqüífer. Els resultats han demostrat el gran potencial degradatiu dels sediments, que a la llarga es podrien potenciar com a biobarrera natural del sistema per tal de prevenir que les aigües contaminades arribin a l'aigua superficial del riu Zenne.
This thesis is based on the study of bioremediation processes as reliable technologies to remove contaminants from groundwater.
Specifically, it is aimed to study denitrification and reductive dechlorination as bioremediation technologies to remove nitrates and chlorinated aliphatic hydrocarbons (CAHs), respectively, from polluted groundwater. In addition, it is aimed to apply advanced technologies which allow improving on the knowledge of these processes.
The aquifer associated to the Stream Argentona, located in Argentona, Catalunya (Spain), was selected as study site to investigate the denitrification process. In the first part, microcosm experiments containing groundwater and subsoil from the aquifer were performed. From these first studies it was observed the low capacity of the aquifer to eliminate nitrates under natural conditions, but, at the same time, it was noted the feasibility of applying a bioremediation process such as the addition of organic matter. In addition, the influence of different factors such as the presence of oxygen and the type of electron donor on the denitrification process was studied.
Afterwards, a mathematical model was developed to explain the microbiological processes that occur when stimulating the aquifer material with an organic carbon source. The model could successfully explain the consumption of oxygen, nitrates and organic matter by the indigenous facultative heterotrophic microbial population from aquifer. Some parameters of the model were calibrated from experimental data and the quality of these parameters was investigated. The developed model constitutes a first approach in order to have reliable models for in situ denitrification.
In order to advance in the study of the denitrification process in natural conditions, dynamic experiments were carried out simulating the groundwater flow through the aquifer. The efficiency of injecting organic matter under these conditions was demonstrated. At the same time, hydrodynamic effects of the process were observed, indicating the importance to design properly bioremediation technologies before its application in field-scale. Furthermore, an integrated model coupling the biochemical reactions and the transport processes inside the column was developed and applied to describe denitrification under dynamic conditions.
Finally, molecular microbiological techniques were applied to investigate microbial changes due to the application of enhanced denitrification. On the one hand, real-time polymerase chain reaction (real-time PCR) assays revealed the growth of microbial population, specially of denitrifying bacteria in aquifer material stimulated with an organic carbon source. On the other hand, the denaturing gradient gel electrophoresis (DGGE) method allowed to investigate changes in the indigenous microbial community due to the amendment with organic matter.
In order to advance in the knowledge of bioremediation processes in groundwater, reductive dechlorination of CAHs in groundwater was studied. In this case, experiments at laboratory scale were applied, aimed to study the possible application of a permeable reactive barrier (PRB) to eliminate a CAH-contaminated plume, containing basically cis-1,2-dichloroethene and vinyl chloride, which flows to the River Zenne near Brussels, Belgium.
The study included batch experiments in order to investigate the degradation potential in aquifer and sediments of the River Zenne, as well as column experiments which simulated the groundwater flow through the sediments of the river or the aquifer material. The results demonstrated the high degradation potential of the sediments, which in the long term could be enhanced to act as a natural biobarrier of the system in order to prevent groundwater contaminants from arriving at the surface water of the River Zenne.
15
Parker, Simon John. « Chalk regional groundwater models and their applicability to site scale processes ». Thesis, Imperial College London, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.543348.
Texte intégral
16
Hellawell, Emma Elizabeth. « Modelling transport processes in soil due to hydraulic density and electrical gradients ». Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240839.
Texte intégral
17
Said, Md Azlin b. Md. « Water resources modelling using remotely sensed data ». Thesis, Cardiff University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340765.
Texte intégral
18
Vinciguerra, Cristine M. « Recharge processes within the Cacapon Mountain Aquifer, Ridge and Valley Province, West Virginia ». Morgantown, W. Va. : [West Virginia University Libraries], 2008. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=5575.
Texte intégralRésumé :
Thesis (M.S.)--West Virginia University, 2008.Title from document title page. Document formatted into pages; contains ix, 68 p. : ill. (some col.), maps (some col.). Includes abstract. Includes bibliographical references (p. 64-67).
19
Gao, Hongze. « Modelling geochemical interactions with groundwater transport processes : an application to acid mine drainage ». Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341885.
Texte intégral
20
Berger, Karen Plaut 1972. « Surface water-- groundwater interaction : the spatial organization of hydrologic processes over complex terrain ». Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/80630.
Texte intégral
21
Watson, Ian Andrew. « Modelling of natural attenuation processes in groundwater using adaptive and parallel numerical methods ». Thesis, University of Sheffield, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408300.
Texte intégral
22
Iwasaki, Kenta. « Effects of bedrock groundwater dynamics on hydro-biogeochemical processes in granitic headwater catchments ». Kyoto University, 2018. http://hdl.handle.net/2433/232152.
Texte intégral
23
Heimann, Axel Colin. « Bioenergetics of transient and steady-state anaerobic redox processes relevant to groundwater contamination ». Kgs. Lyngby, 2007. http://www.er.dtu.dk/publications/fulltext/2007/MR2007-082.pdf.
Texte intégral
24
Harbison, John Edwin. « Groundwater chemistry and hydrological processes within a Quaternary coastal plain : Pimpama, Southeast Queensland ». Thesis, Queensland University of Technology, 2007. https://eprints.qut.edu.au/16647/1/John%20Harbison%20Thesis.pdf.
Texte intégralRésumé :
The Pimpama estuarine plain in subtropical southeast Queensland is comprised of Quaternary sediments infilling older bedrock. These multilayered unconsolidated sediments have various depositional origins, and are highly heterogeneous. The plain is low-lying and the surface drainage is controlled by flood mitigation measures including tidal gates and channelised streams. The control of surface drainage potentially affects the shallow water table. This modification of hydrology has implications for future viability of agriculture and also the environmental health of waterways. Increased landscape modification and water management is likely in the coming years. The combination of sediment heterogeneity, low hydraulic gradients, and artificial drainage modification result in the plain being hydrogeologically complex. In order to understand hydrologic processes in this setting, a multi-disciplinary research programme was conducted which included a drilling program, overland electromagnetic induction and other geophysical surveys (downhole gamma log, electromagnetic induction and magnetic susceptibility) to initially establish the geologic framework. These surveys were followed by hydrogeochemical testing which includes for major and minor ions and also stable isotopes, and mineralogical analysis of drillhole material. Underlying basement rock occurs at up to 60 m depth. Unconsolidated gravel and sand deposits occur within incised paleo-valleys and are overlain by predominantly low-permeability fluvial sandy clays and estuarine and lagoonal muds. Fine-grained delta sands occur in the top 15 m of the sub-surface. Within the unconsolidated sediments, hydrodynamic trends clearly discriminated between upper unconfined and lower semi-confined aquifer systems. A comparison of surface water and shallow groundwater levels indicate limited interaction of groundwater and surface water. Hydrogeochemical analysis effectively distinguished between groundwater bodies, and also distinguished saline groundwater from seawater. Trends in major ion chemistry in the semi-confined system (particularly Na/Cl and Ca/Cl ratios) showed ion exchange accompanying saline intrusion. However, due to factors such as mineral dissolution, major ion chemistry does not clearly identify solute flux trends in the shallow aquifer system. Water stable isotope analysis (δ18O and δ2H) indicated the provenance of fresh and saline groundwater and also the relative importance of the principal hydrologic processes, i.e. evaporation and water uptake by plants. Groundwater exhibited a wide range in salinity, from very fresh to hypersaline. The formation of hypersaline groundwater was attributed largely to uptake of water by mangrove forests. Since mangrove forests were more extensive at the time of the Holocene maximum sea level (approximately 6,000 years ago) than at present, some of this groundwater may represent relict salinity from this earlier time. The relationship of relict salinity to low permeability sediments, particularly at intermediate depths, and their depositional history was examined. Vertical salinity gradients and hydrogeochemistry within these sediments varied according to position within the plain, suggesting deposition under various hydrological and sea level regimes. A preliminary investigation using analysis of stable sulfate isotopes (δ34S and δ18OSO4) was made. This study shows substantial potential for the application of this technique for quantification of solute flux and sulfur chemical transformations within settings such as this coastal plain. To establish shallow groundwater flow processes, a MODFLOW-based numerical model was used to inversely estimate aquifer parameters under various recharge scenarios. The model was designed to examine the relative importance of evapotranspiration and discharge to surface waters. However, largely due to the complexity of the drainage network and non-uniform surface water flows, the quantification of surface water- groundwater interaction by consideration of hydrodynamics is problematic. Therefore, the chemistry of groundwater and surface water was compared. While the estimated contribution of rainfall to groundwater level fluctuations was significant (46%), high evapotranspiration rates reduced net recharge and it was concluded that baseflow to drains and creeks during dry periods was insignificant, and groundwater velocities in the shallow aquifer are low. The study illustrates the value of both hydrodynamic and hydrogeochemical analyses in estuarine settings where relict salinity and groundwater-aquifer interactions impact significantly on water quality. Saline groundwater is chemically distinct from theoretical mixtures of seawater and freshwater. The study also demonstrates the value of particular chemical parameters, e.g. Na/Cl and SO4/Cl ratios and stable water isotopes, for identifying hydrologic processes in this setting.
25
Harbison, John Edwin. « Groundwater chemistry and hydrological processes within a Quaternary coastal plain : Pimpama, Southeast Queensland ». Queensland University of Technology, 2007. http://eprints.qut.edu.au/16647/.
Texte intégralRésumé :
The Pimpama estuarine plain in subtropical southeast Queensland is comprised of Quaternary sediments infilling older bedrock. These multilayered unconsolidated sediments have various depositional origins, and are highly heterogeneous. The plain is low-lying and the surface drainage is controlled by flood mitigation measures including tidal gates and channelised streams. The control of surface drainage potentially affects the shallow water table. This modification of hydrology has implications for future viability of agriculture and also the environmental health of waterways. Increased landscape modification and water management is likely in the coming years. The combination of sediment heterogeneity, low hydraulic gradients, and artificial drainage modification result in the plain being hydrogeologically complex. In order to understand hydrologic processes in this setting, a multi-disciplinary research programme was conducted which included a drilling program, overland electromagnetic induction and other geophysical surveys (downhole gamma log, electromagnetic induction and magnetic susceptibility) to initially establish the geologic framework. These surveys were followed by hydrogeochemical testing which includes for major and minor ions and also stable isotopes, and mineralogical analysis of drillhole material. Underlying basement rock occurs at up to 60 m depth. Unconsolidated gravel and sand deposits occur within incised paleo-valleys and are overlain by predominantly low-permeability fluvial sandy clays and estuarine and lagoonal muds. Fine-grained delta sands occur in the top 15 m of the sub-surface. Within the unconsolidated sediments, hydrodynamic trends clearly discriminated between upper unconfined and lower semi-confined aquifer systems. A comparison of surface water and shallow groundwater levels indicate limited interaction of groundwater and surface water. Hydrogeochemical analysis effectively distinguished between groundwater bodies, and also distinguished saline groundwater from seawater. Trends in major ion chemistry in the semi-confined system (particularly Na/Cl and Ca/Cl ratios) showed ion exchange accompanying saline intrusion. However, due to factors such as mineral dissolution, major ion chemistry does not clearly identify solute flux trends in the shallow aquifer system. Water stable isotope analysis (δ18O and δ2H) indicated the provenance of fresh and saline groundwater and also the relative importance of the principal hydrologic processes, i.e. evaporation and water uptake by plants. Groundwater exhibited a wide range in salinity, from very fresh to hypersaline. The formation of hypersaline groundwater was attributed largely to uptake of water by mangrove forests. Since mangrove forests were more extensive at the time of the Holocene maximum sea level (approximately 6,000 years ago) than at present, some of this groundwater may represent relict salinity from this earlier time. The relationship of relict salinity to low permeability sediments, particularly at intermediate depths, and their depositional history was examined. Vertical salinity gradients and hydrogeochemistry within these sediments varied according to position within the plain, suggesting deposition under various hydrological and sea level regimes. A preliminary investigation using analysis of stable sulfate isotopes (δ34S and δ18OSO4) was made. This study shows substantial potential for the application of this technique for quantification of solute flux and sulfur chemical transformations within settings such as this coastal plain. To establish shallow groundwater flow processes, a MODFLOW-based numerical model was used to inversely estimate aquifer parameters under various recharge scenarios. The model was designed to examine the relative importance of evapotranspiration and discharge to surface waters. However, largely due to the complexity of the drainage network and non-uniform surface water flows, the quantification of surface water- groundwater interaction by consideration of hydrodynamics is problematic. Therefore, the chemistry of groundwater and surface water was compared. While the estimated contribution of rainfall to groundwater level fluctuations was significant (46%), high evapotranspiration rates reduced net recharge and it was concluded that baseflow to drains and creeks during dry periods was insignificant, and groundwater velocities in the shallow aquifer are low. The study illustrates the value of both hydrodynamic and hydrogeochemical analyses in estuarine settings where relict salinity and groundwater-aquifer interactions impact significantly on water quality. Saline groundwater is chemically distinct from theoretical mixtures of seawater and freshwater. The study also demonstrates the value of particular chemical parameters, e.g. Na/Cl and SO4/Cl ratios and stable water isotopes, for identifying hydrologic processes in this setting.
26
Martinez, Jorge L. « Revealing groundwater-surface water exchanges and recharge processes with multiple tracers and hydrochemistry ». Thesis, Queensland University of Technology, 2017. https://eprints.qut.edu.au/110526/1/Jorge_Martinez_Thesis.pdf.
Texte intégralRésumé :
For effective resource management and to establish groundwater and surface water interactions, an innovative range of hydrological tracers and hydrochemical techniques have been applied to a total catchment in southeast Queensland. Stable and radioisotopes, carbon-14, radon-222, noble gases and SF6 were analyzed to characterize and quantify recharge sources. Statistical methods were also combined with inverse geochemical and three-dimensional geological modelling techniques, to develop regional conceptual models of groundwater movement and interaction with rivers.
27
Koelsch, Roger Sebastian. « Effect of floods and recovering aquatic vegetation on surface and subsurface storage processes at Pinal Creek, Globe, Arizona ». Thesis, The University of Arizona, 2000. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_etd_hy0222_sip1_w.pdf&type=application/pdf.
Texte intégral
28
Trupiano, Vito. « EVALUATION OF OXIDIZED MEDIA FILTRATION PROCESSES FOR THE TREATMENT OF HYDROGEN SULFIDE IN GROUNDWATER ». Master's thesis, University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3026.
Texte intégralRésumé :
This study evaluated alternative sulfide treatment processes for potable water systems that rely on groundwater supplies. Research for this study was conducted at the Imperial Lakes (IL) and Turner Road (TR) water treatment plants (WTPs) in Polk County, Florida. These WTPs are in the process of refurbishment and expansion, and will require the installation of a new groundwater well. The IL and TR WTPs both rely upon groundwater sources that contain total sulfide at concentrations ranging from 1.4 to 2.6 mg/L. Sulfide is a concern because if left untreated it can impact finished water quality, corrosivity, create undesirable taste and odor, and oxidize to form visible turbidity. For this reason, the raw water will require treatment per Florida Department of Environmental Protection (FDEP) "Sulfide Rule" 62-555.315(5)(a). This rule does not allow the use of conventional tray aeration (currently in use at the IL and TR WTPs) for wells that have significant total sulfide content (0.6 to 3.0 mg/L). This research was commissioned because the potential water treatment method identified in the Sulfide Rule (i.e. forced-draft aeration) would not adequately fit within the confines of the existing sites and would pose undue burden to neighboring residents. In addition, an effective sulfide treatment process was desired that offered a low profile, did not necessitate the need for additional complex chemical feed systems, minimized the extent of electrical infrastructure upgrades, and was inexpensive to construct and operate. To meet these goals, several alternative technologies were evaluated at the desktop and bench-scale; these included anion exchange, various oxidation methods, and alternative media filtration processes. From that effort, several processes were selected for evaluation at the pilot scale: bleach (NaOCl) oxidation preceding electromedia filtration; manganese (IV) oxide (MnO2) filtration continuously regenerated with bleach; and ferrate (Fe(VI)) oxidation. Electromedia and MnO2 filtration were shown to be effective for total sulfide treatment. Both processes reduced total sulfide content to below detection levels (< 0.1 mg/L) for groundwater supplies containing as much as 2.6 mg/L of total sulfide. The use of bleach oxidation ahead of media filtration also produced finished water with low turbidity (< 1.0 NTU) as compared to conventional tray aeration and chlorination processes (6-16 NTU, as observed in this study). It was determined that the media filtration approach (electromedia and MnO2) was effective for sulfide treatment and met the County's site objectives established at the outset of the project. Ferrate was also shown to reduce total sulfide content to below detection levels (< 0.1 mg/L) for groundwater supplies containing as much as 2.6 mg/L of total sulfide. An opinion of probable capital costs for installing a sulfide oxidation/filtration process at either the Imperial Lakes or Turner Road WTP was estimated to range from roughly $830,000 to $1,100,000. That equates to a $/kgal capital cost of $0.10 to $0.32 (at 8% for 20 years). An opinion of annual probable bleach chemical costs was estimated to range from $3,500 to $9,800 for the IL WTP and $3,500 to $5,800 for the TR WTP.M.S.Env.E.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Environmental Engr MSEnvE
29
Martin, Caroline Elizabeth Anne. « Sources of solutes, groundwater fluxes and weathering processes in an active mountain belt, Taiwan ». Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648850.
Texte intégral
30
Libelo, Edward Laurence. « Studies on processes controlling the input of agricultural chemicals in groundwater to surface waters ». W&M ScholarWorks, 1995. https://scholarworks.wm.edu/etd/1539616742.
Texte intégralRésumé :
This dissertation describes several studies of groundwater quality, the fate and transport of nutrients and atrazine in groundwater systems and physical processes at the sediment-water interface which impact on groundwater discharge. Groundwater monitoring wells were installed at the Goodwins Island and Catlett Island NERRS sites in Virginia and agricultural, suburban and forest land use sites in the York and James River Basins. Groundwater was analyzed for nutrients, pH, salinity and trace organics. Shoreline land use, associated nutrient loading and an estimate of total groundwater flux suggest that groundwater contributes up to 30% of the total nitrogen input to the Chesapeake Bay. Batch isotherm K&\sb{lcub}\rm d{rcub}& values for &\sp{14}&C-labelled atrazine sorption to low organic carbon (OC) aquifer solids ranged from 0.08 to 0.61 L/kg, much lower than for soil and other, higher carbon, solids. Kd was dependent on the surface area (SA) and surface iron (SFe), and can be described by:&&\rm K\sb{lcub}d{rcub} = 0.046(SA)+ 0.61(SFe) + 0.83&&. Kinetics of atrazine sorption onto low OC sediments showed an initial rapid reaction accounting for &>&95% of sorption within a few minutes at about 2 &\mu&g kg&\sp{lcub}-1{rcub}& min&\sp{lcub}-1{rcub}& followed by a slower (0.003 &\mu&g kg&\sp{lcub}-1{rcub}& min&\sp{lcub}-1{rcub}&) reaction. Comparison of homogeneous and heterogeneous atrazine hydrolysis reaction rates at elevated temperature showed no evidence for catalysis by aquifer solids. A physical mechanism for passive ventilation of relict biological structures in the benthic boundary layer is presented, a mathematical model of circulation in surrounding sediments was solved analytically and MODFLOW used to numerically determine induced hydraulic gradients and flow. Hydraulic head in surrounding sediments can be reduced by several centimeters in a zone extending over several hundred cm&\sp2&, and pore velocities of &>&10&\sp{lcub}-3{rcub}& cm/s and flux rates of tens to hundreds of mL/hr induced. Flume and field studies showed that large variability and poor repeatability of seepage meter measurements may be due to surface water flow across the meter. Pressure gradients in the boundary layer reduce hydraulic head within the meter and induce augmented seepage flow. Covering the seepage meter collection bag to isolate it from flow can reduce or eliminate this error.
31
Schilling, Keith Edwin. « Hydrological processes inferred from water table fluctuations, Walnut Creek, Iowa ». Diss., University of Iowa, 2009. https://ir.uiowa.edu/etd/430.
Texte intégralRésumé :
In a shallow aquifer underlain by low permeable material, groundwater recharge (R), discharge to rivers or stream as baseflow (BF), and discharge to the atmosphere as evapotranspiration (ET) are related by a simple water balance equation, R - ET - BF = ΔS. Gathering information about these processes is difficult since these processes are hidden from view, yet these processes commingle with one another at the water table surface. The main objective of this dissertation project was to evaluate how main hydrological processes can be inferred from high-resolution water table measurements collected at various sites in Walnut Creek watershed located in southern Iowa. Water table monitoring data available for analysis in the project included three main sites, covering 2573 days between 1996 to 2008 and 61,714 individual water level monitoring points. Water table fluctuations were used to estimate R across an upland-floodplain chronosequence and plant ET under three riparian land covers. High resolution hydraulic head measurements were analyzed with spectral methods to evaluate potential surface and groundwater interaction. Detailed sedimentology and water table monitoring were combined to develop a conceptual model of nitrate leaching to in the near-stream riparian zone of an incised channel. Additional soil moisture and precipitation monitoring are recommended for improved application of methods to other sites. Results from this dissertation indicate that there is a considerable amount of information about key hydrological processes to be gained by measuring water table levels at a high frequency.
32
Vandemoer, Catherine 1955. « The hydrogeochemistry of recharge processes and implications for water management in the southwestern United States ». Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/191146.
Texte intégralRésumé :
A geochemical approach to the evaluation of the chemistry of natural recharge processes in the Tucson basin was used to identify the major minerals controlling the evolution of ground water chemistry and to assess the viability of recharging imported Central Arizona Project water supplies. Well cuttings analyses and water quality samples from over 65 wells in the basin were used as input to the geochemical computer model PATH4 (Helgeson, 1970) and the sequence of aqueous species and mineral production in a recharge reference volume examined. The study reveals that natural processes in the basin lead to the increase in dissolved solids content in ground water over time and the production of secondary minerals such as calcite, calcium montmorillonite, kaolinite and poorly crystallized alumino-silicate phases. Secondary minerals grow into aquifer pore spaces and may, over time, be responsible for the reduction in aquifer porosity and the specific capacity of wells. The recharge of imported Central Arizona Project water will lead to an increase in the dissolved solids content of ground water and may, in certain areas of the basin, lead to the enhanced production of secondary minerals. The use of CAP water as a recharge source must be guided by the geochemical factors which influence the nature and scope of reactions between CAP water and the Tucson aquifer matrix. The study demonstrates the need for and identifies water quality and aquifer matrix criteria for the assessment of sources of recharge water and recharge facility sites. The use of geochemistry as a tool for quantitatively assessing ground water quality is demonstrated.
33
Nash, David J. « The development and environmental significance of the dry valley systems (mekgacha) in the Kalahari, central southern Africa ». Thesis, University of Sheffield, 1992. http://etheses.whiterose.ac.uk/5976/.
Texte intégralRésumé :
The dry valley systems in the Kalahari of southern Africa are traditionally considered to have developed as a result of past fluvial activity. However, it has also been suggested that erosion by groundwater processes (sapping and deep-weathering) had an important role in development. This thesis aims to establish the relative role of each of these process areas in mekgacha evolution using a combined geological and geomorphological approach. The study area is restricted to the valley systems of Botswana, eastern Namibia and the Northern Cape Province of South Africa, which can be subdivided into exorcic and endoreic systems directed towards the Orange River and the continental interior, respectively. Field studies, analyses of remotely-sensed imagery and a consideration of network orientation identify evidence for the role of both fluvial and groundwater processes in valley development. However, whilst both groups of processes have operated, the importance of each is suggested to have varied both spatially and temporally. Fluvial processes are indicated by sequences of sediments, relict channels and terrace levels, and appear to have operated most recently. Sapping processes are implied in the formation of certain valley systems, primarily from morphological properties and the presence of relict spring lines. Deep-weathering processes are implicated from the close parallelism of many valleys with geological structures now buried beneath thicknesses of Kalahari Group sediments. Borehole records also indicate deep-weathering of bedrock beneath valleys developed above fracture zones, which is suggested to have operated over the longest timescales. Thin-section studies of duricrusts from valley flanks, together with duricrust profiles and records from lithological boreholes, indicate the role of groundwater in their formation. Results suggest an intrinsic link between duricrust formation and valley development. Geochemical and thin-section analyses of duricrusts further suggest that previous considerations of the palaeoenvironmental significance of Kalahari silcretes based upon TiO2 levels may not be wholly appropriate.
34
Issa, Sanaa. « Hydrogeologic and 3-D Shallow Groundwater Flow Integrated Study and Salinisation Processes with Some Areas at Western Sydney, New South Wales, Australia ». Thesis, The University of Sydney, 2018. http://hdl.handle.net/2123/20915.
Texte intégralRésumé :
In South Western Sydney (which encompasses the study area), New South Wales, Australia, salinity is a major emerging urban problem and is primarily related to rising groundwater level. This eight-chapter thesis focuses on the factors influencing salinity and its processes in the Mount Annan, Currans Hills and Narellan Vale areas, and investigates both the present three-dimensional (3-D) groundwater flow pattern and that expected to occur in the area as a result of future urban expansion. The chemical and physical analyses carried out on the soil samples collected from the study areas, and the groundwater level and electrical conductivity data have been interpreted in a comprehensive integrated manner to identify factors and processes influencing salinity, and to develop a reliable and detailed hydrogeological conceptual model. A new method has been developed for groundwater recharge estimation for unconfined aquifers under the assumption that groundwater recharge is solely due to rainfall. The method is capable of estimating groundwater recharge and drainage and predicting groundwater levels from time series of observed groundwater level data and rainfall events. The method can produce non-unique solution. Despite the non-uniqueness, the estimated recharges do not suffer large variations. A 3-D groundwater flow model has been developed by calibrating the measured groundwater level data using the MODFLOW code. The groundwater flow maps constructed from the 3-D calibration results have shown that the flow pattern is collectively controlled by topography and recharge, and varies in space and time, which likely suggests that the salinisation process, which is influenced by the lateral and vertical groundwater movements, varies in space and time. Analysis has revealed that future urbanisation likely results in changes in the subsurface water balance. Conclusions and suggested avenues for future research are drawn in Chapter 8.
35
Choudhury, Zubaida Akhtar. « Groundwater arsenic pollution in Bangladesh : a study of water consumption behaviour and decision-making processes within rural communities ». Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610220.
Texte intégral
36
Tharamapalan, Jayapregasham. « Application and Optimization of Membrane Processes Treating Brackish and Surficial Groundwater for Potable Water Production ». Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5530.
Texte intégralRésumé :
The research presented in this dissertation provides the results of a comprehensive assessment of the water treatment requirements for the City of Sarasota. The City's drinking water supply originates from two sources: (1) brackish groundwater from the Downtown well field, and (2) Floridan surficial groundwater from the City's Verna well field. At the time the study was initiated, the City treated the brackish water supply using a reverse osmosis process that relied on sulfuric acid for pH adjustment as a pretreatment method. The Verna supply was aerated at the well field before transfer to the City's water treatment facility, either for softening using an ion exchange process, or for final blending before supply. For the first phase of the study to evaluate whether the City can operate its brackish groundwater RO process without acid pretreatment, a three-step approach was undertaken that involved: (1) pilot testing the plan to reduce the dependence on acid, (2) implementing the plan on the full-scale system with conservative pH increments, and (3) continuous screening for scale formation potential by means of a “canary” monitoring device. Implementation of the study was successful and the annual savings in operating expenditure to the City is projected to be about $120,000. From the acid elimination study, using the relationship between electrical conductivity in water and total dissolved solids in water samples tested, a dynamic approach to evaluate the performance of the reverse osmosis plant was developed. This trending approach uses the mass transfer coefficient principles of the Homogeneous Solution Diffusion Model. Empirical models were also developed to predict mass transfer coefficients for solutes in terms of total dissolved solids and sodium. In the second phase of the study, the use of nanofiltration technology to treat aerated Verna well field water was investigated. The goal was to replace the City's existing ion exchange process for the removal of hardness and total dissolved solids. Different pretreatment options were evaluated for the nanofiltration pilot to remove colloidal sulfur formed during pre-aeration of the groundwater. Sandfilters and ultrafiltration technology were evaluated as pretreatment. The sandfilter was inadequate as a pre-screen to the nanofiltration pilot. The ultrafiltration pilot (with and without a sandfilter as a pre-screen) proved to be an adequate pretreatment to remove particulates and colloids, especially the sulfur colloids in the surficial groundwater source. The nanofiltration pilot, was shown to be an efficient softening process for the Verna well field water, but it was impacted by biofoulants like algae. The algae growth was downstream of the ultrafiltration process, and so chlorination was used in the feed stream of the ultrafiltration process with dechlorination in the nanofiltration feed stream using excess bisulfite to achieve stable operations. Non-phosphonate based scale inhibitors were also used to reduce the availability of nutrients for biofilm growth on the nanofiltration membranes. The combined ultrafiltration-nanofiltration option for treatment of the highly fouling Verna water samples is feasible with chlorination (to control biofouling) and subsequent dechlorination. Alternatively, the study has shown that the City can also more economically and more reliably use ultrafiltration technology to filter all water from its Verna well field and use its current ion exchange process for removal of excess hardness in the water that it supplies.Ph.D.
Doctorate
Civil, Environmental, and Construction Engineering
Engineering and Computer Science
Environmental Engineering
37
White, Bradley A. « Physical Investigation of Field Scale Groundwater Recharge Processes in the Virginia Blue Ridge Physiographic Province ». Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/36297.
Texte intégralRésumé :
Physical and geophysical data collected at the Fractured Rock Research Site in Floyd County, Virginia indicate that recharge rates to the subsurface are controlled by a small scale thrust fault associated with regional thrust faulting within the Blue Ridge Province. Recharge rates appear to be correlated to spatial variation in the hydraulic conductivity of the regolith, which has been influenced by weathering rates and the metamorphic and structural history of the underlying parent material. Previous studies conducted at the Fractured Rock Research Site suggest that recharge potential can be separated into two regions: one over a vertically oriented shear zone associated with the small scale thrust fault, and the other overlying a thrust fault hanging wall. The angle of dip of the thrust fault shear zone and the fracturing within the crystalline rock adjacent to the fault plane appear to serve as geologic controls that preferentially direct infiltrated meteoric water to a deeper confined aquifer. The structural competence of the granulite gneiss thrust fault hanging wall appears to act as a barrier to deeper groundwater recharge, causing the formation of a shallow semi-confined aquifer within the overlying regolith.
In-situ analysis of matric potential and moisture content shows two distinctly different recharge processes that are spatially correlated with the structure of the shallow subsurface (regolith overlying the vertically oriented shear zone and regolith overlying the thrust fault hanging wall), and have been shown to have strong temporal correlations with the dynamics of the underlying saturated conditions.
Recharge flux estimates within the regolith overlying the thrust fault hanging wall are uncharacteristically high, and appear to be offset within the monitored region by the upward hydraulic gradient associated with the potentiometric surface of the underlying semi-confined aquifer. Because of the influence exerted by the upward hydraulic gradient on matric potential within the unsaturated regolith overlying the semi-confined aquifer, accurate recharge estimates could not be obtained from the matric potential data recorded by the tensiometers along this portion of the transect. Recharge flux within the regolith overlying the vertically oriented shear zone is strongly controlled by the orientation and aerial extent of the thrust fault shear zone, and highlights the importance of accurate delineation of recharge areas in crystalline rock aquifer systems.
Master of Science
38
Desilets, Sharon. « Flood Processes in Semi-arid Streams : Sediment Transport, Flood Routing, and Groundwater - Surface Water Interactions ». Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/195652.
Texte intégralRésumé :
Flooding in semi-arid streams is highly variable but distinguished from its humid counterpart in terms of forcing conditions, landscape response, flood severity, and stream-aquifer connectivity. These floods have the potential for great benefit in a water-limited environment, but also great devastation when powerful floods encounter human infrastructure. This dissertation employs an integrative approach to address several facets of flooding in semi-arid streams. In particular, information from field sampling during flood events combined with modeling are used to evaluate the processes of post-disturbance sediment transport, flood routing, transient bank storage, and stream disconnection. The major findings show: (1) Suspended sediment composition in floods following wildfire depends on the number, timing, and intensity of preceding storms and flood events, implicating overland flow hillslope processes as a dominant mass wasting mechanism (2) Isotopic chemographs for two representative intense convective storm events demonstrate that the flash flood bore develops from predominantly high elevation event water that overcomes, incorporates, and pushes baseflow to the front of the hydrograph peak (3) Isotope information combined with a plug-flow model can simulate this flood bore mixing process simultaneously in two separate canyons in the basin in order to calculate the timing and quantity of flow; this could be a useful tool for watersheds that are not extensively instrumented, or for calibrating a more complex or distributed model, (4) For a stream connected to an underlying aquifer, a circulation pattern develops at the onset of flooding that causes an upwelling of antecedent water into the unsaturated zone, challenging the assumptions of one dimensional, lateral flow and transport into the streambank, and (5) For small stream-aquifer disconnections, large increases in infiltration, large decreases in seepage, and a dominantly vertical profile for floodwater were observed. This implies that a stream that supports a wide riparian corridor may be in danger of vegetation die-offs with even shallow depletions of the groundwater table.
39
Magnone, Daniel. « Modelling the sources of organic material, processes and timescales leading to arsenic contamination of circum-Himalayan groundwaters ». Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/modelling-the-sources-of-organic-material-processes-and-timescales-leading-to-arsenic-contamination-of-circumhimalayan-groundwaters(852ae5a1-b09a-44fd-99b3-d8ae2dcc65c6).html.
Texte intégralRésumé :
Arsenic contamination of circum-Himalayan groundwater is leading to one of the greatest humanitarian disasters of modern times, poisoning at least 70 million people who are mostly poor and rural. The groundwater is hosted in Holocene aquifers consisting of Himalayan sediments deposited by the great Asian rivers in deltaic environments. Arsenic is released when organic material (OM) reacts with the iron-oxide minerals co-deposited in the sediments onto which arsenic is adsorbed. The source of OM is one of the most important questions facing researchers and policy makers. There are generally accepted to be three potential sources of OM: 1) sedimentary bound OM (SOM) co-deposited with sediments; 2) thermally mature petroleum upwelled from reservoirs below the aquifers; 3) dissolved organic carbon (DOC) some of which might be drawn in to the aquifer through modern pumping and irrigation. In this thesis the nature of organic material in the aquifer is researched and the processes and timescales which lead to arsenic release are studied. Here evidence for a new conceptual model of arsenic release is presented. Isotopic tracing combined with a new geochemical model and organic geochemical techniques, shows that OM driving arsenic release pre-dates agriculture in the region and was from natural grasslands in the early Holocene. The geochemical model utilises strontium isotopes to correct the radiocarbon age of dissolved inorganic carbon (DIC) to find only the age and isotopic signature of DIC from oxidation of organic material. This shows that DIC from oxidation of OM was from the early Holocene and had an isotopic signature consistent with the early Holocene SOM in this region. A study of the sediments in the region built upon a geomorphological history shows that the most oxidised SOM is from early Holocene sediments. Thus both techniques separately indicate that pre-agricultural organic material drove arsenic release. This conceptual model however reveals the "arsenic sand paradox", because whilst release is from early Holocene clays, today highest concentrations of arsenic are in younger sands. Explaining this paradox is the most important next step leading on from this research.
40
Davididou, Konstantina. « Sustainable photocatalytic oxidation processes for the treatment of emerging microcontaminants ». Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31339.
Texte intégralRésumé :
This work investigates the elimination of new and emerging microcontaminants (EMs) from water by means of photochemical oxidation processes, namely heterogeneous and homogeneous photocatalysis. Representative compounds of artificial sweeteners (saccharin, SAC), endocrine disruptors (bisphenol-A, BPA), and pharmaceutica ls (antipyrine, AP) of high environmental persistence and widespread occurrence in the water cycle are used as case studies. Novel concepts that can make photochemica l oxidation a more cost-effective and environmentally benign technology are tested. In Chapter 4, the photocatalytic treatment of SAC and BPA is investigated. Novel submicronic anatase-rutile nanocomposite particles with tuned phase ratio are used as catalysts to increase the photocatalytic performance under UVA irradiation. At the best-assayed conditions (C0 = 3 mg/L, catalyst = 400 mg/L), SAC and BPA are completely degraded within 90 and 150 min of photocatalytic treatment, respectively. [variables: anatase-rutile ratio; initial substrate concentration; catalyst concentration; catalyst reuse; sonication during catalyst recovery] In Chapter 5, a UVA light-emitting diode (UVA-LED) and sunlight are used as irradiation sources to reduce energy requirements and environmental impacts of photocatalytic processes. The photocatalytic degradation of SAC and BPA is studied under UVA irradiation provided by either a UVA-LED or a conventional fluoresce nt blacklight UVA lamp (UVA-BL) and solar irradiation. At the best-assayed conditions (C0 = 2.5 mg/L, TiO2 = 250 mg/L), BPA is completely degraded within 20, 30, and 120 min under UVA-LED, solar, and UVA-BL irradiation, respectively. The treatment time required for the complete elimination of SAC is 20 min under UVA-LED and 90 min under UVA-BL irradiation. [variables: initial substrate concentration; catalyst concentration; water matrix; light source; reactor configuration] In Chapter 6, a comparative study is carried out among the photocatalytic systems of Chapters 4 and 5 in terms of EMs removal, photonic and energy efficiencies. Technica l and economic aspects of all the processes are assessed. LED-driven photocatalysis achieves the highest efficiency in terms of organic removal with the minimum energy consumption, rendering it the most sustainable technology for the treatment of EMs. In Chapter 7, olive mill wastewater (OMW) is used as an iron-chelating agent in the photo-Fenton reaction to obviate the need for water acidification at pH 2.8. Conventional, OMW- and EDDS-assisted photo-Fenton treatment is applied for SAC degradation in a solar compound parabolic collector (CPC). It was found that OMW forms iron complexes able to catalyse H2O2 decomposition and generate hydroxyl radicals. At the optimal OMW dilution (1:800), 90% of SAC is degraded within 75 min. [variables: pH; iron-chelating agent; initial SAC concentration; OMW dilution] In Chapter 8, other complexing and oxidising agents, namely oxalate and persulfate, are used for the intensification of AP degradation during UVA-LED photo-Fenton treatment. Neural networks are applied for process modelling and optimisation. At the optimal conditions (hydrogen peroxide = 100 mg/L, ferrous iron = 20 mg/L, oxalic acid = 100 mg/L), complete degradation of AP and 93% mineralisation is achieved within 2.5 and 60 min, respectively. [variables: initial concentration of hydrogen peroxide, ferrous iron, oxalic acid, persulfate] It is concluded that LED-driven photocatalysis is a sustainable technology for the elimination of EMs from water. Results from this work highlight the need for development and optimisation of engineering proper LED reactors. Furthermore, this work introduces a new concept towards the sustainable operation of photo-Fenton that is based on the use of wastewaters rich in polyphenols instead of pricey and hazardous chemicals for iron chelation. The addition of ferrioxalate complexes is proposed for the intensification of EMs mineralisation during UVA-LED photo-Fenton treatment. Finally, the findings of this work encourage the use of chemometric tools as predictive and optimisation tools.
41
Brauner, J. Steven. « Impacts of Sequential Microbial Electron Accepting Processes on Natural Attenuation of Selected Petroleum Hydrocarbons in the Subsurface Environment ». Diss., Virginia Tech, 2000. http://hdl.handle.net/10919/26339.
Texte intégralRésumé :
Regulatory acceptance of monitored natural attenuation (MNA) requires demonstration that natural processes, such as sorption and biodegradation, attenuate specific contaminants of concern on a time scale that is comparable to other remediation options while concurrently preventing contaminant migration to site-specific points of contact. Two of the tools used to demonstrate the efficacy of MNA, microcosm experiments and numerical fate and transport modeling, were examined in this study. In the first phase of this work, laboratory microcosm studies were initiated as part of an overall MNA site assessment to determine whether a native microbial consortia collected with a soil sample from a petroleum-hydrocarbon contaminated site was capable of biodegrading specific polynuclear aromatic hydrocarbon (PAH) compounds. Results indicated that selected PAH compounds were biodegraded under simulated natural conditions using oxygen and sulfate as electron acceptors. In the second phase of this study, a numerical experiment was conducted using the three-dimensional, multiple substrate, multiple electron acceptor fate and transport model SEAM3D (Waddill and Widdowson, 1997) to evaluate the impact of including iron(III)-reducing conditions during numerical simulations of natural attenuation. Results for this phase of the study indicated that the mass of hydrocarbon simulated as biodegraded by the iron(III)-reducing population was significantly larger than hydrocarbon biodegradation under aerobic conditions. The final component of research used the SEAM3D model to interpret field observations recorded during a natural attenuation experiment where the fate and transport of selected hydrocarbon contaminants (BTEX and naphthalene) was tracked through an extremely heterogeneous, but well-instrumented test aquifer. Results from the calibrated model for the NATS experiment indicated that the majority of the contaminant remained in the non-aqueous phase during the first year of the experiment, and that aerobic biodegradation was the dominant natural attenuation process. Model results were particularly sensitive to the rate of contaminant release and the starting mass of electron acceptor.Ph. D.
42
Dejwakh, Navid Rene. « Using 15N, 18O, and 17O to Determine Nitrate Sources and Removal Processes from Groundwater, Tucson, Arizona ». Thesis, The University of Arizona, 2008. http://hdl.handle.net/10150/193327.
Texte intégralRésumé :
Nitrate is a common groundwater contaminant. Due to adverse health effects, waters above the Maximum Contaminant Level (MCL) of 10 mg NO3-N/L or 0.71 mmols/L, are banned from domestic consumption by the EPA. Studies have measured elevated nitrate concentrations in arid land soils and groundwater around the world. These elevated concentrations could be detrimental to the environment and to human health. Thus, it is important to consider the different sources and processes affecting nitrate concentrations Here, a novel triple isotope system approach was employed, coupling δ17O with δ18O and δ15N of nitrate to determine the sources (atmospheric, terrestrial, fertilizer, wastewater) and removal processes influencing nitrate concentrations in the Tucson basin groundwater system. Results show low groundwater nitrate concentrations (0.2 mmols/L) where wastewater was not a predominant source of water, versus high concentrations (1 mmols/L) above the MCL in groundwaters where wastewater was the dominant water source. Furthermore, groundwater up to 1.6 Km away from the wastewater stream was contaminated with effluent recharge waters. In addition, denitrification was inferred from δ18O and δ15N data with this inference reinforced by δ17O data and δ15N enrichments up to 26. Finally, low atmospheric nitrate was measured in groundwater, representing up to 6% of total nitrate. The triple isotope approach studied here is ideal for determining the proportion of atmospheric nitrate versus other terrestrial nitrate sources and the significance of nitrate removal processes.
43
Chen, Kouping. « Impact of land reclamation on hydrogeochemical processes in coastal aquifer systems : a case study in Shenzhen, China / ». Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/HKUTO/record/B39558940.
Texte intégral
44
Sidborn, Magnus. « Modelling long-term redox processes and oxygen scavenging in fractured crystalline rocks ». Doctoral thesis, Stockholm : Kemiteknik, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4491.
Texte intégral
45
Ezzy, Timothy Robert. « Integrated Approach to Characterisation of Coastal Plain Aquifers and Groundwater Flow Processes : Bells Creek Catchment, Southeast Queensland ». Thesis, Queensland University of Technology, 2005. https://eprints.qut.edu.au/16166/1/Tim_Ezzy_Thesis.pdf.
Texte intégralRésumé :
Low-lying coastal plains comprised of unconsolidated infill are internally complex
hydrogeological settings, due to the high level of heterogeneity in the infill material.
In order to resolve the hydrogeological processes active in these complex settings, an
integrated multi-disciplinary, geoscientific approach is required. This research
determines quantitatively, the effects of sedimentary aquifer heterogeneity on
groundwater flowpaths and groundwater processes within a heavily laterised, coastal
plain setting. The study site is the Bells Creek catchment in southeast Queensland,
Australia. The methodology developed in this study provides a new approach to
enable the determination of groundwater flowpaths and groundwater processes at
macroscale resolution within other shallow alluvial and coastal plain aquifers. The
multi-disciplinary approach utilises sedimentological, geophysical, chronological and
hydrogeological techniques (including hydrochemistry and groundwater flow
modelling) to develop a high-resolution aquifer framework, and to determine
accurately, both groundwater flowpaths and relative flow rates.
Sedimentary framework is confirmed to be the principal factor controlling the
distribution of aquifer permeability pathways in any given setting, and is therefore,
the dominant control over groundwater flow and processes. For the Bells Creek
catchment, interpretation of stratigraphic and sedimentary data allowed the
compilation of a detailed sedimentary framework. This interpretation demonstrated
that weathering of the low-lying arkose sandstone bedrock has developed thick
lateritic profiles. Within the weathering profiles, cemented, iron-rich horizons have
resisted erosion and developed raised and elongated ridges in the modern landscape,
while other clay-rich weathered layers have submitted to erosion and downgraded
around those iron-rich ridges. Consequently, alluvial deposition throughout the Late
Quaternary has been restricted to narrow, and relatively deep valleys containing sandrich
channels, and thin floodplains at shallow depth.
From a hydrogeological perspective, there is significant macroscopic aquifer
heterogeneity between fine-grained lateritic mixed clay layers, floodplain clays, ironcemented
ferricrete horizons, and permeable sand-rich alluvial aquifers. This
variability of aquifer material has created a complex subsurface arrangement of
permeability pathways. Application of Ground Penetrating Radar (GPR) in this setting enabled accurate definition of alluvial channel boundaries and the high degree
of connectedness within the channels themselves. Interpretation of a comprehensive
GPR dataset (that covered the entire catchment) allowed refinement of the
sedimentary framework previously established to develop a detailed threedimensional
aquifer framework.
Finite-difference groundwater modelling and particle tracking analysis (using
MODFLOW and MODPATH) has clearly demonstrated that the macroscopic
heterogeneity within the various aquifer materials of the plain has marked impacts on
groundwater pathways, and especially groundwater travel times. The variability
between a maximum residence time of 18 months for groundwater within the
alluvium, compared to hundreds of years for groundwater within the mixed clay
layers of the laterite, clearly demonstrates the importance of accurately defining the
spatial distribution of the various aquifer materials in a groundwater flow
investigation. In this setting, the interconnection of the narrow alluvial channels
feeding into a deeper alluvial delta has provided an effective conduit for shallow
groundwater flow. The role of the alluvial delta in discharging the bulk of fresh
groundwater from the central plain into the coastal and estuarine aquifers to the east,
is certainly critical in preventing saline intrusion from encroaching further west.
Hydrochemical and isotopic indicators have identified the dominant recharge
processes and groundwater flowpaths within the plain, and indicated that the
processes are strongly related to sub-surface permeability distributions determined in
the aquifer framework (and groundwater modelling), as well as seasonal fluctuations
in rainfall. In the northwest of the plain, sandstone hills provide a delayed and
slightly mineralized component of groundwater recharge into adjacent highly
permeable, unconfined alluvial aquifers; these aquifers also recharge directly via
precipitation. Aluminosilicate weathering in the bedrock hills and eastern peripheries
of the laterised bedrock are a source of excess Na, SiO2, and HCO3 to the alluvial
groundwater. As this groundwater flows down-gradient to the east, however, its
chemical composition evolves by sulfate reduction, silica equilibrium and ion
exchange processes into a more mature Na-Cl type.
Within the shallow coastal aquifers proximal to the eastern shoreline, sulfate
enrichment is occurring (associated with increases in Ca, HCO3, Fe and Al) resulting
in major deterioration in groundwater quality. The deterioration is produced by saline
intrusion from the adjacent estuary coupled with oxidation of sulfide materials in
shallow marine and estuarine clays. Reverses in salinity in those coastal aquifers have
been correlated with surges in fresh recharge waters from unconfined coastal dunes
and semi-confined landward alluvium, following significant rainfall events.
The multi-disciplinary methodology developed, provides an effective approach for
accurately defining the three-dimensional distribution of shallow aquifer material of
varying permeability via detailed stratigraphic interpretation and GPR analysis.
Utilising this aquifer framework, finite-difference groundwater modelling aided by
hydrogeological data and hydrochemical analysis, allows accurate determination of
groundwater flowpaths and groundwater processes. This research provides a new
hydrogeological analogue for alluvial channel aquifers within a laterised coastal plain
setting.
Key Words:
groundwater flow, aquifer heterogeneity, numerical modelling, hydrochemistry,
recharge, ground penetrating radar, coastal plain aquifers, weathering, alluvial
channels.
46
Ezzy, Timothy Robert. « Integrated Approach to Characterisation of Coastal Plain Aquifers and Groundwater Flow Processes : Bells Creek Catchment, Southeast Queensland ». Queensland University of Technology, 2005. http://eprints.qut.edu.au/16166/.
Texte intégralRésumé :
Low-lying coastal plains comprised of unconsolidated infill are internally complex hydrogeological settings, due to the high level of heterogeneity in the infill material. In order to resolve the hydrogeological processes active in these complex settings, an integrated multi-disciplinary, geoscientific approach is required. This research determines quantitatively, the effects of sedimentary aquifer heterogeneity on groundwater flowpaths and groundwater processes within a heavily laterised, coastal plain setting. The study site is the Bells Creek catchment in southeast Queensland, Australia. The methodology developed in this study provides a new approach to enable the determination of groundwater flowpaths and groundwater processes at macroscale resolution within other shallow alluvial and coastal plain aquifers. The multi-disciplinary approach utilises sedimentological, geophysical, chronological and hydrogeological techniques (including hydrochemistry and groundwater flow modelling) to develop a high-resolution aquifer framework, and to determine accurately, both groundwater flowpaths and relative flow rates. Sedimentary framework is confirmed to be the principal factor controlling the distribution of aquifer permeability pathways in any given setting, and is therefore, the dominant control over groundwater flow and processes. For the Bells Creek catchment, interpretation of stratigraphic and sedimentary data allowed the compilation of a detailed sedimentary framework. This interpretation demonstrated that weathering of the low-lying arkose sandstone bedrock has developed thick lateritic profiles. Within the weathering profiles, cemented, iron-rich horizons have resisted erosion and developed raised and elongated ridges in the modern landscape, while other clay-rich weathered layers have submitted to erosion and downgraded around those iron-rich ridges. Consequently, alluvial deposition throughout the Late Quaternary has been restricted to narrow, and relatively deep valleys containing sandrich channels, and thin floodplains at shallow depth. From a hydrogeological perspective, there is significant macroscopic aquifer heterogeneity between fine-grained lateritic mixed clay layers, floodplain clays, ironcemented ferricrete horizons, and permeable sand-rich alluvial aquifers. This variability of aquifer material has created a complex subsurface arrangement of permeability pathways. Application of Ground Penetrating Radar (GPR) in this setting enabled accurate definition of alluvial channel boundaries and the high degree of connectedness within the channels themselves. Interpretation of a comprehensive GPR dataset (that covered the entire catchment) allowed refinement of the sedimentary framework previously established to develop a detailed threedimensional aquifer framework. Finite-difference groundwater modelling and particle tracking analysis (using MODFLOW and MODPATH) has clearly demonstrated that the macroscopic heterogeneity within the various aquifer materials of the plain has marked impacts on groundwater pathways, and especially groundwater travel times. The variability between a maximum residence time of 18 months for groundwater within the alluvium, compared to hundreds of years for groundwater within the mixed clay layers of the laterite, clearly demonstrates the importance of accurately defining the spatial distribution of the various aquifer materials in a groundwater flow investigation. In this setting, the interconnection of the narrow alluvial channels feeding into a deeper alluvial delta has provided an effective conduit for shallow groundwater flow. The role of the alluvial delta in discharging the bulk of fresh groundwater from the central plain into the coastal and estuarine aquifers to the east, is certainly critical in preventing saline intrusion from encroaching further west. Hydrochemical and isotopic indicators have identified the dominant recharge processes and groundwater flowpaths within the plain, and indicated that the processes are strongly related to sub-surface permeability distributions determined in the aquifer framework (and groundwater modelling), as well as seasonal fluctuations in rainfall. In the northwest of the plain, sandstone hills provide a delayed and slightly mineralized component of groundwater recharge into adjacent highly permeable, unconfined alluvial aquifers; these aquifers also recharge directly via precipitation. Aluminosilicate weathering in the bedrock hills and eastern peripheries of the laterised bedrock are a source of excess Na, SiO2, and HCO3 to the alluvial groundwater. As this groundwater flows down-gradient to the east, however, its chemical composition evolves by sulfate reduction, silica equilibrium and ion exchange processes into a more mature Na-Cl type. Within the shallow coastal aquifers proximal to the eastern shoreline, sulfate enrichment is occurring (associated with increases in Ca, HCO3, Fe and Al) resulting in major deterioration in groundwater quality. The deterioration is produced by saline intrusion from the adjacent estuary coupled with oxidation of sulfide materials in shallow marine and estuarine clays. Reverses in salinity in those coastal aquifers have been correlated with surges in fresh recharge waters from unconfined coastal dunes and semi-confined landward alluvium, following significant rainfall events. The multi-disciplinary methodology developed, provides an effective approach for accurately defining the three-dimensional distribution of shallow aquifer material of varying permeability via detailed stratigraphic interpretation and GPR analysis. Utilising this aquifer framework, finite-difference groundwater modelling aided by hydrogeological data and hydrochemical analysis, allows accurate determination of groundwater flowpaths and groundwater processes. This research provides a new hydrogeological analogue for alluvial channel aquifers within a laterised coastal plain setting. Key Words: groundwater flow, aquifer heterogeneity, numerical modelling, hydrochemistry, recharge, ground penetrating radar, coastal plain aquifers, weathering, alluvial channels.
47
Menz, Christian [Verfasser]. « Oxygen delivering processes in groundwater and their relevance for iron-related well clogging processes– a case study on the quaternary aquifers of Berlin / Christian Menz ». Berlin : Freie Universität Berlin, 2016. http://d-nb.info/1108270883/34.
Texte intégral
48
Haricombe, Erin. « Transport and fate of chemical and microbial tracers at University of Western Cape (UWC) campus site, Cape Flats aquifer of South Africa ». University of the Western Cape, 2016. http://hdl.handle.net/11394/5233.
Texte intégralRésumé :
>Magister Scientiae - MScExtreme weather events in combination with geographical changes in groundwater utilization, groundwater availability, aquifer recharge, and ultimately changes in the quality of water resources, are expected in the future. As a consequence of changing weather patterns and urbanization the demand for groundwater is likely to increase in certain areas. We know that most waterborne pathogenic health epidemics are associated with contamination of farm water and wastewater. There is however limited understanding of the nature and extent of chemical, physical and biological processes that control the fate and transport of the microorganisms in primary and secondary aquifers. In this thesis, transport results are reported, where E. coli and PDR1 were selected as the biological tracers transported through a primary aquifer at the University of the Western Cape. In conjunction with the microbes salt and Rhodamine (chemical tracers) were injected to compare their fate and transport mechanism in the primary aquifer medium. A series of controlled Darcy experiments under laboratory and field conditions were conducted. Each provided a different data and information. The results from laboratory studies were used to improve design of the field studies. In both cases, the data collected provided information on fate and transport of microbes in groundwater. The field design phase of the experiment was an up-scaling of the laboratory phase of this project. The amount of chemical tracers injected into the aquifer was increased in proportion to the size of the research site. Tracer tests using chemical and microbial tracers were conducted simultaneously. Results of laboratory tests demonstrate a 5 times slower transport of microbes, compared to tests with salts during the laboratory phase. The salts at field scale show a breakthrough occurring after 2 days whereas the microbes –did not break through during the 28 days of the observation period. A new borehole was drilled closer to the pumping borehole to eliminate distance or travel time, but this had no effect on field results for the microbes.
National Research Foundation
49
Callahan, Michael Kroh. « Groundwater Controls on Physical and Chemical Processes in Streamside Wetlands and Headwater Streams in the Kenai Peninsula, Alaska ». Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5347.
Texte intégralRésumé :
For this dissertation I studied groundwater and surface water interactions in the Kenai Lowlands, Alaska. In particular, I examine two important aspects of groundwater and surface water interactions: 1) Groundwater's influence on surface-water temperature; and 2) Groundwater's role in forming hydrologic flow paths that can connect uplands to streamside wetlands and streams. Chapter 2 investigates the controls on stream temperature in salmon-bearing headwater streams in two common hydrogeologic settings: 1) drainage-ways, which are low-gradient streams that flow through broad valleys; and 2) discharge-slopes, which are high gradient streams that flow through narrow valleys. The results from chapter 2 showed significant differences in stream temperatures between the two hydrogeologic settings. Observed stream temperatures were higher in drainage-way sites than in discharge-slope sites, and showed strong correlations as a continuous function with the calculated topographic metric flow-weighted slope. Additionally, modeling results indicated that the potential for groundwater discharge to moderate stream temperature is not equal between the two hydrogeologic settings, with groundwater having a greater moderating effect on stream temperature at the low gradient drainage-way sites. Chapter 3 examines the influence of groundwater on juvenile coho salmon winter habitat along the Anchor River. Two backwater habitats were selected from the larger set of 25 coho overwintering sites from a previous study for an in-depth hydrologic analysis. The results from chapter 3 showed that the type of groundwater discharge (i.e., focused versus diffuse groundwater discharge) can play an important role in determining habitat suitability in these backwater sites. During winter, focused discharge from a local groundwater seep maintained higher surface-water temperatures and higher concentrations of dissolved oxygen compared to the site with more diffuse groundwater discharge. Chapter 4 investigates the linkages along hydrologic flow paths among alder (Alnus spp.) stands, streamside wetlands, and headwater streams. Chapter 4 tested four related hypotheses: 1) groundwater nitrate concentrations are greater along flow paths with alder compared to flow paths without alder; 2) on hillslopes with alder, groundwater nitrate concentrations are highest when alder stands are located near the streamside wetlands at the base of the hillslope; 3) primary production of streamside wetland vegetation is N limited and wetlands are less N limited when alder stands are located nearby along flow paths; and 4) stream reaches at the base of flow paths with alder have higher nitrate concentrations than reaches at the base of flow paths without alder. The results from chapter 4 showed that groundwater nitrate concentrations were highest along flow paths with alder, however no difference was observed between flow paths with alder located near versus alder located further from streamside wetlands. Vegetation had a greater response to N fertilization in streamside wetlands that were connected to flow paths without alder and less when alder stands were near. Finally, higher nitrate concentrations were measured in streams at the base of flow paths with alder. The combined results of this dissertation showed that, in the Kenai Lowlands, groundwater and surface water interactions have a direct influence on the local ecology and that a fundamental understanding of the hydrology can aid in the successful management and protection of this unique and important ecosystem.
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Trammell, Erick Jaime. « Groundwater, land use and land cover change in the Ash Meadows National Wildlife Refuge from 1948 to 1998 ». abstract and full text PDF (free order & ; download UNR users only), 2006. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1433352.
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