Philippe Orban

Comparison of methods for the detection and extrapolation of trends in groundwater quality.

Land use changes and the intensification of agriculture since the 1950s have resulted in a deterioration of groundwater quality in many European countries. For the protection of groundwater quality, it is necessary to (1) assess the current groundwater quality status, (2) detect changes or trends in groundwater quality, (3) assess the threat of deterioration and (4) predict future changes in groundwater quality. A variety of approaches and tools can be used to detect and extrapolate trends in groundwater quality, ranging from simple linear statistics to distributed 3D groundwater contaminant transport models. In this paper we report on a comparison of four methods for the detection and extrapolation of trends in groundwater quality: (1) statistical methods, (2) groundwater dating, (3) transfer functions, and (4) deterministic modeling. Our work shows that the selection of the method should firstly be made on the basis of the specific goals of the study (only trend detection or also extrapolation), the system under study, and the available resources. For trend detection in groundwater quality in relation to diffuse agricultural contamination, a very important aspect is whether the nature of the monitoring network and groundwater body allows the collection of samples with a distinct age or produces samples with a mixture of young and old groundwater. We conclude that there is no single optimal method to detect trends in groundwater quality across widely differing catchments.

Coupling heat and chemical tracer experiments for estimating heat transfer parameters in shallow alluvial aquifers

Geothermal energy systems, closed or open, are increasingly considered for heating and/or cooling buildings. The efficiency of such systems depends on the thermal properties of the subsurface. Therefore, feasibility and impact studies performed prior to their installation should include a field characterization of thermal properties and a heat transfer model using parameter values measured in situ. However, there is a lack of in situ experiments and methodology for performing such a field characterization, especially for open systems. This study presents an in situ experiment designed for estimating heat transfer parameters in shallow alluvial aquifers with focus on the specific heat capacity. This experiment consists in simultaneously injecting hot water and a chemical tracer into the aquifer and monitoring the evolution of groundwater temperature and concentration in the recovery well (and possibly in other piezometers located down gradient). Temperature and concentrations are then used for estimating the specific heat capacity. The first method for estimating this parameter is based on a modeling in series of the chemical tracer and temperature breakthrough curves at the recovery well. The second method is based on an energy balance. The values of specific heat capacity estimated for both methods (2.30 and 2.54MJ/m(3)/K) for the experimental site in the alluvial aquifer of the Meuse River (Belgium) are almost identical and consistent with values found in the literature. Temperature breakthrough curves in other piezometers are not required for estimating the specific heat capacity. However, they highlight that heat transfer in the alluvial aquifer of the Meuse River is complex and contrasted with different dominant process depending on the depth leading to significant vertical heat exchange between upper and lower part of the aquifer. Furthermore, these temperature breakthrough curves could be included in the calibration of a complex heat transfer model for estimating the entire set of heat transfer parameters and their spatial distribution by inverse modeling.

Underground pumped storage hydroelectricity using abandoned works (deep mines or open pits) and the impact on groundwater flow

Underground pumped storage hydroelectricity (UPSH) plants using open-pit or deep mines can be used in flat regions to store the excess of electricity produced during low-demand energy periods. It is essential to consider the interaction between UPSH plants and the surrounding geological media. There has been little work on the assessment of associated groundwater flow impacts. The impacts on groundwater flow are determined numerically using a simplified numerical model which is assumed to be representative of open-pit and deep mines. The main impact consists of oscillation of the piezometric head, and its magnitude depends on the characteristics of the aquifer/geological medium, the mine and the pumping and injection intervals. If an average piezometric head is considered, it drops at early times after the start of the UPSH plant activity and then recovers progressively. The most favorable hydrogeological conditions to minimize impacts are evaluated by comparing several scenarios. The impact magnitude will be lower in geological media with low hydraulic diffusivity; however, the parameter that plays the more important role is the volume of water stored in the mine. Its variation modifies considerably the groundwater flow impacts. Finally, the problem is studied analytically and some solutions are proposed to approximate the impacts, allowing a quick screening of favorable locations for future UPSH plants.RésuméDes centrales hydroélectriques de pompage-turbinage utilisant un réservoir souterrain (UPSH Underground pumped storage hydroelectricity) constitué d’une carrière ou d’une mine profonde permettent de stocker l’excès d’électricité produite au cours des périodes de faible demande dans des régions sans relief. Il est essentiel de prendre en considération l’interaction entre les systèmes UPSH et le milieu géologique encaissant. Peu de travail existe concernant l’évaluation des impacts induits sur les écoulements d’eaux souterraines. Ceux-ci sont déterminés numériquement à l’aide d’un modèle numérique simplifié pour lequel on fait l’hypothèse qu’il est représentatif de considérer un puits ouvert de large diamètre. Le principal impact est une oscillation du niveau piézométrique dont l’amplitude dépend des caractéristiques de l’aquifère/milieu géologique, de la mine et des cycles de pompage et d’injection. Si un niveau piézométrique moyen est considéré, celui-ci diminue au début de la mise en activité du système UPSH et puis revient progressivement à son état initial. Les conditions hydrogéologiques les plus favorables pour minimiser les impacts ont été évaluées en comparant plusieurs scénarios. Comme attendu, l’amplitude de l’impact sera la plus faible dans un milieu géologique de faible diffusivité hydraulique. Cependant, le paramètre qui joue le rôle le plus important est le volume d’eau stocké dans la mine. Sa variation modifie de manière considérable les impacts sur les écoulements d’eaux souterraines. Finalement, le problème est étudié de manière analytique et des solutions sont proposées pour évaluer les impacts, permettant un premier tri rapide des sites favorables pour implanter de futures installations UPSH.ResumenLas centrales hidroeléctricas reversibles utilizando un embalse subterráneo (UPSH Underground Pumped Storage Hydroelectricity) formado por una mina a cielo abierto o subterránea permiten almacenar el exceso de electricidad producida durante períodos de baja demanda en regiones llanas. Es esencial tener en cuenta la interacción entre los sistemas UPSH y el medio geológico circundante. Existen pocos trabajos acerca de la evaluación de los impactos sobre el agua subterránea. Estos son determinados numéricamente utilizando un modelo simplificado que se supone representativo de minas subterráneas y a cielo abierto. El principal impacto consiste en la oscilación del nivel piezométrico, y su magnitud depende de las características del acuífero/medio geológico, la mina y los intervalos de bombeo e inyección. Si se considera un nivel piezométrico promedio, este decrece al inicio de la actividad del sistema UPSH y luego recupera progresivamente hasta su estado inicial. Las condiciones hidrogeológicas más favorables para minimizar los impactos son evaluadas comparando varios escenarios. La magnitud del impacto será menor en medios geológicos con baja difusividad hidráulica. Sin embargo, el volumen de agua almacenada en la mina es el parámetro que desempeña el papel más importante. Su variación modifica considerablemente los impactos sobre el flujo de agua subterránea. Por último, el problema se estudia analíticamente y se proponen algunas soluciones para evaluar los impactos. Estas soluciones permiten seleccionar rápidamente los sitios favorables para la construcción de futuras instalaciones UPSH.摘要在平坦地区可以利用露天矿坑或深矿井建造地下抽水蓄能电站,储存能源需求低的时期多余的电。充分考虑地下抽水蓄能电站和周围地质介质的相互作用必不可少。过去几乎没有对相关的地下水流影响做过评价。利用一个假定能够代表露天矿坑和深矿井的简化数值模型确定了对地下水流的影响。主要影响包括测压水头的振荡,其幅度取决于含水层/地质介质的特征、矿井和抽水注水的间隔。如果考虑平均测压水头,测压水头在地下抽水蓄能电站运行开始后初期下降,然后逐渐恢复。通过比较不同的几个方案,评价了使影响达到最小的最有利水文地质条件。水利扩散系数低的地质介质影响幅度较低。然而,发挥重要作用的参数是矿井储存水量。其变化可大大更改对地下水流的影响。最后,分析研究了出现的问题,提出了粗略估算影响的解决方法,可使人们对未来的地下抽水蓄能电站有利位置做出快速筛选.ResumoUsinas hidrelétricas reversíveis subterrâneas (UHRS) utilizando minas a céu aberto ou minas subterrâneas podem ser utilizadas em regiões planas para armazenamento do excedente da energia elétrica produzida durante períodos de baixa demanda energética. É essencial considerar a interação entre as UHRS e o meio geológico do entorno. Poucos estudos têm sido realizados na avaliação dos impactos associados ao fluxo das águas subterrâneas. Os impactos no fluxo das águas subterrâneas são determinados numericamente utilizando modelos numéricos simplificados, considerados representativos para minas a céu aberto e minas subterrâneas. Os principais impactos consistem na oscilação do nível piezométrico, e sua magnitude depende das características do aquífero/meio geológico, da mina e dos intervalos de bombeamento e injeção. Assumindo um nível piezométrico médio, há um declínio que sucede o início das atividades da UHRS, seguido de uma recuperação progressiva. As condições hidrogeológicas mais favoráveis para minimizar os impactos são avaliadas através da comparação de diversos cenários. A magnitude do impacto será inferior em meios geológicos de baixa difusividade hidráulica. Entretanto, o parâmetro que desempenha o papel mais importante é o volume da água armazenada na mina. Sua variação modifica consideravelmente os impactos no fluxo das águas subterrâneas. Por fim, o problema é estudado analiticamente e algumas soluções são propostas para aproximar os impactos, permitindo a rápida triagem de locais favoráveis para futuras UHRS.

Development trajectory of an integrated framework for the mitigation of future flood risk: results from the FloodLand project

ABSTRACT In this paper, the development trajectory of an integrated framework for the mitigation of future flood risk of the Ourthe river basin in Belgium is discussed. The paper contributes to the state-of-the-art by presenting an integrated multidisciplinary framework capable of making long-term projections (time horizon 2050 and 2100) with the objective of mitigating future flood risk by proposing alternative land-use scenarios. It bridges numerous different fields, including urban planning, transport engineering, hydrology, geology, environmental engineering, and economics. The overall design and validation results of the different sub-modules of the framework are presented, and ongoing and future enhancements are highlighted.

Hydrogeochemical mechanisms governing the mineralization and elevated fluoride (F -) contents in Precambrian crystalline aquifer groundwater in central Benin, Western Africa

In the central part of Benin (Western Africa), high fluoride F-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}

Large scale surface―subsurface hydrological model to assess climate change impacts on groundwater reserves

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Identification of groundwater quality trends in a chalk aquifer threatened by intensive agriculture in Belgium

\end{document} contents have been reported in groundwater from Precambrian crystalline bedrock aquifer which is the main source of drinking water. The hydrogeochemical mechanisms leading to such elevated fluoride concentrations are usually not fully understood. In this context, the objective is to identify the hydrogeochemical processes governing groundwater mineralization and the origin of the high fluoride concentrations. A dataset of 162 groundwater samples was collected from the aquifer consisting of a thin altered bedrock layer (shallow aquifer) and a deep fractured crystalline bedrock (deep aquifer). Geochemical approaches and multivariate statistics have been used to explore the data. Fluoride concentrations vary between 0.00 and 7.19 mg/L in groundwater. Samples collected in the southern part of the investigated area, close to Dassa-Zoumé, show the highest concentrations, with more than 75% greater than the guideline value of 1.5 mg/L. The deep fractured aquifer shows higher concentrations of fluoride than the shallow regolith reservoir. Results reveal that groundwater mineralization is derived mainly from the hydrolysis of silicate minerals, but it is also influenced by anthropogenic effects, particularly in the shallow reservoir. However, fluoride has a geogenic origin, primarily from the weathering of silicate minerals, primarily biotite. Ca2+/Na+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}