222Rn as Natural Tracer for LNAPL Recovery in a Crude Oil‐Contaminated Aquifer          下载免费PDF全文

Violaine Ponsin  Amélie Chablais  Julien Dumont  Olivier Radakovitch  Patrick Höhener 《Ground Water Monitoring & Remediation》2015,35(2):30-38

The objective of this study was to investigate whether ²²²Rn in groundwater can be used as a tracer for light non‐aqueous phase liquid (LNAPL) quantification at a field site treated by dual‐phase LNAPL removal. After the break of a pipeline, 5 ha of soil in the nature reserve Coussouls de Crau in southern France was contaminated by 5100 m³ of crude oil. Part of this oil seeped into the underlying gravel aquifer and formed a floating oil body of about 3.9 ha. The remediation consists of plume management by hydraulic groundwater barriers and LNAPL extraction in the source zone. ²²²Rn measurements were performed in 21 wells in and outside the source zone during 15 months. In uncontaminated groundwater, the radon activity was relatively constant and remained always >11 Bq/L. The variability of radon activity measurements in wells affected by the pump‐and‐skim system was consistent with the measurements in wells that were not impacted by the system. The mean activities in wells in the source zone were, in general, significantly lower than in wells upgradient of the source zone, owing to partitioning of ²²²Rn into the oil phase. The lowest activities were found in zones with high non‐aqueous phase liquid (NAPL) recovery. LNAPL saturations around each recovery well were furthermore calculated during a period of high groundwater level, using a laboratory‐determined crude oil–water partitioning coefficient of 38.5 ± 2.9. This yielded an estimated volume of residual crude oil of 309 ± 93 m³ below the capillary fringe. We find that ²²²Rn is a useful and cheap groundwater tracer for finding zones of good LNAPL recovery in an aquifer treated by dual‐phase LNAPL removal, but that quantification of NAPL saturation using Rn is highly uncertain.  相似文献   

Modeling coastal tsunami hazard from submarine mass failures: effect of slide rheology,experimental validation,and case studies off the US East Coast     

Grilli  Stéphan T.  Shelby  Mike  Kimmoun  Olivier  Dupont  Guillaume  Nicolsky  Dmitry  Ma  Gangfeng  Kirby  James T.  Shi  Fengyan 《Natural Hazards》2017,86(1):353-391

Natural Hazards - We perform numerical simulations to assess how coastal tsunami hazard from submarine mass failures (SMFs) is affected by slide kinematics and rheology. Two types of two-layer SMF...  相似文献   

Hydrothermal calderas     

Olivier Merle  Stéphanie Barde-Cabusson  Benjamin van Wyk de Vries 《Bulletin of Volcanology》2010,72(2):131-147

The standard model of caldera formation is related to the emptying of a magma chamber and ensuing roof collapse during large eruptions or subsurface withdrawal. Although this model works well for numerous volcanoes, it is inappropriate for many basaltic volcanoes (with the notable exception of Hawaii), as these have eruptions that involve volumes of magma that are small compared to the collapse. Many arc volcanoes also have similar oversized depressions, such as Poas (Costa Rica) and Aoba (Vanuatu). In this article, we propose an alternative caldera model based on deep hydrothermal alteration of volcanic rocks in the central part of the edifice. Under certain conditions, the clay-rich altered and pressurized core may flow under its own weight, spread laterally, and trigger very large caldera-like collapse. Several specific mechanisms can generate the formation of such hydrothermal calderas. Among them, we identify two principal modes: mode 1: ripening with summit loading and flank spreading and mode II: unbuttressing with flank subsidence and flank sliding. Processes such as summit loading or flank subsidence may act simultaneously in hybrid mechanisms. Natural examples are shown to illustrate the different modes of formation. For ripening, we give Aoba (Vanuatu) as an example of probable summit loading, while Casita (Nicaragua) is the type example of flank spreading. For unbuttressing, Nuku Hiva Island (Marquesas) is our example for flank subsidence and Piton de la Fournaise (La Réunion) is our example of flank sliding. The whole process is slow and probably needs (a) at least a few tens of thousands of years to deeply alter the edifice and reach conditions suitable for ductile flow and (b) a few hundred years to achieve the caldera collapse. The size and the shape of the caldera strictly mimic that of the underlying weak core. Thus, the size of the caldera is not controlled by the dimensions of the underlying magma reservoir. A collapsing hydrothermal caldera could generate significant phreatic activity and trigger major eruptions from a coexisting magmatic complex. As the buildup to collapse is slow, such caldera-forming events could be detected long before their onset.  相似文献   

Influence of shallow infiltration on time-lapse ERT: Experience of advanced interpretation   总被引：1，自引：0，他引：1  

Rémi Clément  Marc Descloitres  Thomas Günther  Olivier Ribolzi  Anatoli Legchenko 《Comptes Rendus Geoscience》2009,341(10-11):886-898

Previous time-lapse Electrical Resistivity Tomography (ERT) studies have experienced difficulties in reconstructing reliable calculated resistivity changes in the subsurface. Increases or decreases of resistivity appear in the calculated ERT image where no changes were noted in the subsurface, leading to erroneous hydrological interpretations of the geophysical results. In this article, we investigate how a variation of actual resistivity with time and at shallow depth can influence time-lapse ERT results and produce resistivity artefacts at depth. We use 1 and 2-D numerical modelling to simulate infiltration scenarios. Using a standard time-lapse inversion, we demonstrate the resistivity artefact production according to the electrode spacing parameter. We used an advanced inversion methodology with a decoupling line at shallow depth to attenuate or remove resistivity artefacts. We also applied this methodology to a field data set obtained in a semi-arid environment in Burkina Faso, West Africa. Here, time-lapse ERT shows several resistivity artefacts of calculated resistivity if a standard inversion is used. We demonstrate the importance of a dense sampling of shallow resistivity variations at shallow depth. Advanced interpretation allows us to significantly attenuate or remove the resistivity artefact production at intermediate depth and produce reliable interpretation of hydrological processes.  相似文献   

Sediment fingerprinting in fluvial systems： review of tracers,sediment sources and mixing models   总被引：3，自引：0，他引：3  

Arman HADDADCHI  Darren S. RYDER  Olivier EVRARD  Jon OLLEY 《国际泥沙研究》2013,28(4):560-578

Suspended sediments in fluvial systems originate from a myriad of diffuse and point sources, with the relative contribution from each source varying over time and space. The process of sediment fingerprinting focuses on developing methods that enable discrete sediment sources to be identified from a composite sample of suspended material. This review identifies existing methodological steps for sediment fingerprinting including fluvial and source sampling, and critically compares biogeochemical and physical tracers used in fingerprinting studies. Implications of applying different mixing models to the same source data are explored using data from 41 catchments across Europe, Africa, Australia, Asia, and North and South America. The application of seven commonly used mixing models to two case studies from the US （North Fork Broad River watershed） and France （Bldone watershed） with local and global （genetic algorithm） optimization methods identified all outputs remained in the acceptable range of error defined by the original authors. We propose future sediment fingerprinting studies use models that combine the best explanatory parameters provided by the modified Collins （using correction factors） and Hughes （relying on iterations involving all data, and not only their mean values） models with optimization using genetic algorithms to best predict the relative contribution of sediment sources to fluvial systems.  相似文献   

The catastrophe structure of thermohaline convection in a two-dimensional fluid model and a comparison with low-order box models     

Olivier Thual  James C. Mcwilliams 《地球物理与天体物理流体动力学》2013,107(1-4):67-95

Abstract

We impose a surface forcing on the 2D, Boussinesq, thermohaline equations in a rectangular domain, in the form of equatorially symmetric cosine distributions of salinity flux and temperature. This system may be seen as an idealization of the ocean thermohaline circulation on the global scale over intervals of centuries or millenia. Multiple steady states are found numerically. They reflect the competition between the opposite signs of the temperature and salinity-driven equatorially symmetric circulations. There are also pole-to-pole, equatorially asymmetric circulations. In the control space of the temperature and salinity-flux forcing amplitudes, these equilibria form two cusp catastrophes, and transitions between stable equilibria occur through several distinct bifurcations. These catastrophes can be reproduced in simple box models connecting stirred reservoirs through capillary pipes. This steady-state analysis may provide a framework for a better understanding of climatic transitions between different stable regimes of the ocean-atmosphere system.  相似文献   

Application du réseau des neurones artificiels à la prévision des débits horaires: Cas du bassin versant de l’Eure,France     

Ouissem Kharroubi  Olivier Blanpain  Eric Masson  Sami Lallahem 《水文科学杂志》2013,58(3):541-550

RÉSUMÉ

Les modèles pluie–débit sont fortement utilisés dans la gestion des risques hydrologiques et la prévision des crues. Dans cette étude, nous présentons un modèle pluie–débit pour la prévision des débits horaires basé sur la technique des réseaux de neurones artificiels (RNA). Ce modèle a été développé et appliqué sur le bassin versant de l’Eure au Nord-Ouest de la France afin de dépasser les problèmes dus à la non-linéarité de la relation pluie–débit et à l’imprécision des données collectées. La création de ce modèle a nécessité plusieurs étapes pendant lesquelles nous avons pu déterminer les paramètres du modèle permettant la compréhension de la complexité hydrologique et la production des informations nécessaires à la prévision. Elles ont abouti à un modèle de réseau de neurones artificiels capable d’effectuer, en quelques secondes, des prévisions des crues efficaces jusqu’à un horizon de prévision de 48 h. Ces résultats confirment que les modèles RNA peuvent jouer un rôle important dans le domaine de la prévision car capables de modéliser la non-linéarité des relations pluie–débit rencontrées sur certains bassins hydrologiques.