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Tracking reactive processes in low permeability sediments and their effect on contaminant longevity in aquifers using compound-specific isotope analysis

Applicant Hunkeler Daniel
Number 166233
Funding scheme Project funding (Div. I-III)
Research institution Centre d'hydrogéologie et de géothermie Université de Neuchâtel
Institution of higher education University of Neuchatel - NE
Main discipline Other disciplines of Environmental Sciences
Start/End 01.03.2017 - 28.02.2021
Approved amount 471'451.00
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Keywords (3)

isotopes; degradation; aquitards

Lay Summary (German)

Lead
Chlorierte Lösungsmittel sind die am häufigsten in Altlasten (alte Deponien und Betriebstandorte) auftretende Schadstoffe. Durch ihre grosse Dichte erreichen sie oft auch Grundwasserleiter und treten in Spuren auch in Wasserfassungen auf. Während Laborstudien aufgezeigt haben dass diese Stoffe unter idealen Bedingungen abgebaut werden können ist noch wenig bekannt wie die Eigenschaften des Untergrundes die Ausbreitung und insbesondere die Stärke der Abbauprozesse beeinflussen. und insbesondere welche geologischen Faktoren einen möglichen natürlichen Abbau der Stoffe begünstigen.
Lay summary

Inhalt und Ziel des Forschungsprojekts

Die Zielsetzung des Projekt ist es besser zu verstehen wie der Aufbau des Untergrundes das Verhalten dieser Stoffe beeinflussen. Dabei steht der Einfluss der weit verbreiteten Heterogenität des Untergrundes im Vordergrund d.h. das Auftreten von Wechsellagen mit Schichten in denen sich das Grundwasser unterschiedlich rasch bewegt. Es kann erwartet werden das der Abbau in diesen Schichten unterschiedlich rasch abläuft und sich durch Diffusionsprozesse zwischen den Schichten gegenseitig beeinflusst. Im Projekt wird eine Kombination von detaillierten Feldstudien und mathematischen Modellen verwendet, um den Effekt dieser Prozesse auf die maximale Ausbreitung und die Konzentration der Stoffe zu untersuchen. Gleichzeitig werden auch neue Methoden entwickelt, um den mikrobiellen Abbau unter komplexen geologischen Bedingungen nachweisen zu können.

Wissenschaftlicher und gesellschaftlicher Kontext des Forschungsprojektes

Das Projekt erlaubt es bessere Voraussagen zu machen, wann mit einer weitreichenden und lange anhaltenden Ausbreitung der Stoffe gerechnet werden muss und wann natürliche Prozesse zu deren Rückhalt führen. Entsprechend können die Prioritäten bei der Sanierung von solchen Standorten richtig gesetzt werden und die finanziellen Mittel zielführend dafür eingesetzt werden.

 

Direct link to Lay Summary Last update: 08.09.2016

Responsible applicant and co-applicants

Employees

Publications

Publication
Tracking chlorinated contaminants in the subsurface using compound-specific chlorine isotope analysis: A review of principles, current challenges and applications
Zimmermann Jeremy, Halloran Landon J.S., Hunkeler Daniel (2020), Tracking chlorinated contaminants in the subsurface using compound-specific chlorine isotope analysis: A review of principles, current challenges and applications, in Chemosphere, 244, 125476-125476.
Chlorinated ethene plume evolution after source thermal remediation: Determination of degradation rates and mechanisms
Murray Alexandra Marie, Ottosen Cecilie B., Maillard Julien, Holliger Christof, Johansen Anders, Brabæk Lærke, Kristensen Inge Lise, Zimmermann Jeremy, Hunkeler Daniel, Broholm Mette M. (2019), Chlorinated ethene plume evolution after source thermal remediation: Determination of degradation rates and mechanisms, in Journal of Contaminant Hydrology, 227, 103551-103551.
COMPEST, a PEST-COMSOL interface for inverse multiphysics modelling: Development and application to isotopic fractionation of groundwater contaminants
Halloran Landon J.S., Brunner Philip, Hunkeler Daniel (2019), COMPEST, a PEST-COMSOL interface for inverse multiphysics modelling: Development and application to isotopic fractionation of groundwater contaminants, in Computers & Geosciences, 126, 107-119.
Modelling of C/Cl isotopic behaviour during chloroethene biotic reductive dechlorination: Capabilities and limitations of simplified and comprehensive models
Badin Alice, Braun Fabian, Halloran Landon J. S., Maillard Julien, Hunkeler Daniel (2018), Modelling of C/Cl isotopic behaviour during chloroethene biotic reductive dechlorination: Capabilities and limitations of simplified and comprehensive models, in PLOS ONE, 13(8), e0202416-e0202416.

Collaboration

Group / person Country
Types of collaboration
Stephanie Wirth, University of Neuchatel Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Pilar Junier, University of Neuchâtel Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Prof. Beth Parker, University of Guelph Canada (North America)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel
Danish Technical University Denmark (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Dr. O Shouakar-Stash, University of Waterloo, Canada Canada (North America)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Exchange of personnel

Abstract

Chlorinated hydrocarbons (CHCs) are among the most common groundwater contaminants. CHC are generally released as dense non-aqueous phase liquids (DNAPLs) that accumulate in complex patterns in the subsurface. The persistence of CHC in the subsurface has been explained by the slow dissolution of DNAPLs. More recent research has shown that diffusion into low permeability units and back-diffusion can substantially contribute to contaminant longevity and explain plume persistence even after DNAPL sources have been removed. In low permeability units, geochemical conditions are often more reducing than in the surrounding aquifer hence potentially favouring CHC degradation by abiotic or biotic processes and thus limiting back-diffusion. However, it is also possible that only partial degradation occurs with the formation of more toxic daughter products that back-diffuse into aquifers. The main aim of the project is to improve the current understanding of CHC degradation in low permeability units and its effect on the long term fate of CHCs in aquifer systems. More specifically, the project aims at gaining new insight into the occurrence of transformation processes in low permeability units, the relative importance of abiotic versus biotic transformation, and its effect on contaminant plumes. The project strongly relies on compound-specific isotope analysis (CSIA). The method has the potential to differentiate between transformation mechanisms based on process-specific dual isotope trends and is particularly suited to track slow but yet relevant degradation, which is integrated in the isotope signature over time. The project consists of three parts. In the first part, the additional knowledge required for application of the CSIA approach to low permeability settings is acquired. More information is needed on the effect of sorption on isotope ratios of CHC, as sorption-retarded diffusion is expected to be particularly important in reactive units with a high organic carbon content (WP1). In addition, dual isotope slopes of specific degradation mechanism, especially abiotic transformation by Fe(II)-bearing minerals, need to be better constrained to be able to apply the method for process discrimination (WP2). In part two, detailed multi-isotope profiles (C, Cl, H) are determined for contaminated cores from sites with various geochemical conditions. The possibility to identify transformation processes based on dual isotope trends is explored (WP3). Using core scale numerical models, transformation rates are quantified especially for sites with controlled contaminant releases where the duration of exposure is well constrained. In part three, numerical modeling is employed to evaluate more generally how reactive processes in low permeability units affect the contaminant fate in aquifer systems, how well they can be tracked with CSIA and what type of samples provide most insight (water vs solids). It will also be explored whether time-discrete isotope profiles can be exploited as an archive to reconstruct the history and temporal evolution of reactive processes and whether isotope analysis can distinguish between degradation in the aquifer versus the low permeability units. The project will be carried out by a PhD student (100%) that focuses on WP1, 2 and 3, as well as a postdoc position dedicated to WP4 (50% SNF). The project will be supported by a high-level team with complementary fields of experience. Prof. D. Hunkeler (PI, University of Neuchâtel), a leading expert on isotope methods in contaminant hydrogeology; Prof. B. Parker (Guelph University Canada) a leading expert on contaminant behavior in aquitards; Dr. O. Shouakar-Stash (University of Waterloo, Canada) who has pioneered C und H isotope analysis in CHC; Prof. P. Junier (University of Neuchâtel) a microbial ecologist, and Dr. S. Wirth (University of Neuchâtel), a specialist of geology of lacustrine deposits and techniques to characterize cores from fine-grain, low permeability units.
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