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Pessac, France

Dumont M.,CNRS Paris Institute of Global Physics | Reninger P.A.,Bureau de Recherches Geologiques et Minieres | Pryet A.,ENSEGID | Martelet G.,Bureau de Recherches Geologiques et Minieres | And 2 more authors.
1st European Airborne Electromagnetics Conference - Held at Near Surface Geoscience 2015

Airborne electromagnetic (AEM) methods proved their accuracy in environmental studies during last decades. Volcanic islands are characterized by heterogeneous geology controlled by various complex factors. La Réunion Island, localized in the south-west part of the Indian Ocean, is composed by two shield volcanoes. Their structures are controlled by large erosive processes driven by steep topography, and weathering in inter-tropical climate and the cyclonic regime. In these conditions, in order to help interpreting a large regional AEM dataset resulting in millions of 3D resistivity values, we propose a strategy to delimit areas where the resistivity structure of the first 100 m of the underground have comparable behaviors - And accordingly comparable geological and/or hydrogeological characteristics. Agglomerative Hierarchical Clustering (AHC) analyzes variation between the vertical resistivity distributions of all inverted soundings. AHC results are hierarchized in clusters, each one being associated to an average depth-resistivity signature. The AHC method was applied on the AEM dataset acquired on La Réunion Island. Clusters are consistent with the geological background and inform on different geological and hydrogeological phenomena such as weathering. These subdomains will be used with the aim of evaluating various conceptual hydrogeological models throughout the island. Source

Hohener P.,Aix - Marseille University | Atteia O.,ENSEGID
Geochimica et Cosmochimica Acta

In isotope geochemistry, the Rayleigh equation describes the evolution of isotope ratios in a parent compound as a function of reaction progress, and associated equations describe isotope ratios in an instantaneous product and an accumulated product. The Rayleigh equation is commonly used for fitting fractionation factors of processes undergoing kinetic isotope fractionation such as biochemical reactions. This work extends the equations associated with the Rayleigh equation for describing the isotope ratios in intermediate products in a chain of reacting species degrading with first-order kinetics. A general solution is presented for decay chains of any length, and explicit examples are presented for the biodegradation of a substrate or a mixture of substrates through 3 intermediate products to a final product. Applications of these analytical solutions for the fitting of enrichment factors for intermediate compounds in laboratory experiments are demonstrated with a spreadsheet. This avoids separate experiments to measure each intermediate product. The utility of the equations for the assessment of slopes in dual isotope plots is furthermore illustrated, and limitations of its use are critically discussed. © 2013 Elsevier Ltd. Source

Hohener P.,Aix - Marseille University | Elsner M.,Helmholtz Center Munich | Eisenmann H.,Isodetect GmbH Ingolstadter Landstr. 1 | Atteia O.,ENSEGID
Journal of Contaminant Hydrology

Spills of chloroethenes (CEs) at industrial and urban sites can create groundwater plumes in which tetrachloro- and trichloroethene sequentially degrade to dichloroethenes, vinyl chloride (VC) and ethene, or ethane under reducing conditions. For detoxification, degradation must go beyond VC. Assessments based on ethene and ethane, however, are difficult because these products are volatile, may stem from alternative sources, can be further transformed and are not always monitored. To alternatively quantify degradation beyond VC, stable carbon isotope mass balances have been proposed where concentration-weighted CE isotope ratios are summed up and compared to the original source isotope ratio. Reported assessments, however, have provided not satisfactorily quantified results entailing greatly differing upper and lower estimates. This work proposes an integrative approach to better constrain the extent of total chloroethene degradation in groundwater samples. It is based on fitting of measured concentration and compound-specific stable carbon isotope data to an analytical reactive transport equation simulating steady-state plumes in two dimensions using an EXCEL spreadsheet. The fitting also yields estimates of degradation rates, of source width and of dispersivities. The approach is validated using two synthetic benchmark cases where the true extent of degradation is well known, and using data from two real field cases from literature. © 2015 Elsevier B.V. All rights reserved. Source

Atteia O.,ENSEGID | Del Campo Estrada E.,French National Center for Scientific Research | Bertin H.,French National Center for Scientific Research
Reviews in Environmental Science and Biotechnology

Soil flushing using aqueous solutions is employed to solubilise contaminants. As water solubility is the controlling mechanism of dissolution, additives (surfactants, cosolvents, etc.) are used to enhance efficiencies and reduce the treatment time compared to the use of water alone. The use of surfactant alone gives efficiencies of about 80-85 % in laboratory experiments, but the amounts of product to be injected are very important, which does not seem to be economically sustainable. Studies indicate that when soil flushing is applied in the field, efficiency is very variable; it can vary from almost 0 % to almost 100 %. This illustrates the importance of knowledge of the field (soil heterogeneities, type of contamination, etc.). Using only one product (surfactant, cosolvent, cyclodextrin) often gives moderate efficiencies and needs very large amounts of products, with a product:pollutant ratio higher than 100:1. On the other hand, the use of more complex methods involving micro emulsions or several products with polymer injection lead to high efficiencies at first and a product:pollutant ratio that can be lower than 5. The importance of the initial saturation of the non-aqueous phase liquid is highlighted: the higher the initial saturation, the higher the efficiency. For initial saturations lower than 1 %, soil flushing may not be a very efficient technique. This paper provides an overview of recent studies in the area of soil and groundwater remediation, from laboratory columns scale to pilot and real sites. The research has focused on chlorinated solvents as they are extremely difficult to treat. © 2013 Springer Science+Business Media Dordrecht. Source

Del Campo Estrada E.,French National Center for Scientific Research | Bertin H.,French National Center for Scientific Research | Atteia O.,ENSEGID
Transport in Porous Media

Contamination of soil and groundwater with nonaqueous phase liquid represents a major environmental concern because of the negative effect on human health. Traditional soil flushing techniques have been proved ineffective in heterogeneous aquifers, since liquids for remediation flow preferentially through the most permeable layers and residual oil remains trapped in the low-permeability sediments. To improve the sweep efficiency, fluids with lower mobility than resident liquids can be injected, such as polymers or in situ generated foam. In addition, foam has the potential of selectively reducing mobility in higher-permeability layers compared to lower-permeability layers. The use of foams has not been popular because foam mobility is difficult to predict. In this paper, a series of 1D column experiments were conducted to investigate the variation of the resistance factor RF as a function of the permeability. Five types of sand and calibrated glass beads were used to obtain porous media of permeabilities ranging from 250 millidarcy to 100 Darcy. Two commercial nonionic surfactants, (Formula presented.) X-100 (commonly used but toxic) and sucrose laurate (environmentally friendly surfactant, biodegradable), were used at a concentration equal to 10 critical micelle concentration. Columns were first saturated with water and then flushed with 1.5 PV (pore volumes) of surfactant solution in order to achieve the adsorption of molecules into the soil matrix. Then, co-injection of air and surfactant solution was performed at a constant total rate to generate in situ foam. The quality of the foam was varied from 85 to 99 % to investigate the effect of this parameter on the resistance factor. A graphic showing the dependence of RF and the permeability is presented. Results suggest that for the same total flow rate, the RF decreases as permeability increases, but for permeabilities smaller than 1 Darcy, the RF is weak, probably due to the difficulty to generate stable foam under high capillary pressures. Variations in foam quality and surfactant type do not seem to have an important effect on the results regarding RF. The presented results are assistance for predicting foam behavior in porous media of different permeabilities. © 2015, Springer Science+Business Media Dordrecht. Source

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