Final Report Summary - REACTIVEFLOWS (Reactive transport in subsurface flows. Imaging the flow organisation and predicting solute motion, mixing and reactivity)
Motivation
It has become increasingly apparent over the last 20 to 30 years that European groundwater resources are at risk from a wide variety of stresses including point and diffuse sources of contamination, over-abstraction and saline intrusion. In fact, the problem of a ready supply of clean water for all is global and regarded as one of the biggest challenges of the 21st century (Intergovernmental panel on climate change (IPCC) report 2007). In Europe, these issues are addressed through the Water Framework Directive (WFD) established in 2000 and the Groundwater Directive (GWD) established in 2007, the overall the aim of which is to promote sustainable water use based on long term protection of water bodies in a single management system. These directives fundamentally change the way in which the water industry has operated up to now, presenting both the research and industrial communities with challenging work.
The REACTIVEFLOWS project aims at tackling more specifically the issue of the transport of contaminants in groundwater. The latter is determined by the multi-scale organisation of natural flows (Gelhar, 1993). This complex organisation, due to the existence of heterogeneous geological structures, generally leads to anomalous transport features, such as early or late arrival times and non-Gaussian spatial distributions (Berkowitz et al., 2006). Accounting for these properties is particularly critical for the prediction of contaminant transport in the subsurface. A number of approaches have been developed recently, such as Continuous time random walk (CTRW) theory and fractional Fokker-Planck equations to describe anomalous transport. However, the role of the local flow organisation on effective transport is not yet understood quantitatively (see review of Neuman and Tartakovsky, 2008). When chemical reactions take place, such as dissolution, precipitation, sorption or reactions between aqueous species with possible biological activity, the effect of the flow heterogeneity is even more critical and is not accounted for in most existing theories, which represent a severe limitation of our predictive capabilities (Dentz et al., 2011).
Project objectives
The main objective of the REACTIVEFLOWS project is to establish the link between the characterisation of the flow heterogeneity and the prediction of reactive transport in aquifers. The research methodology is organised into three main goals:
1. develop inverse methods for flow imaging in natural media from geophysical, flow and tracer measurements;
2.quantify the role of the flow organisation on the mixing properties and on the reaction rates, and thus develop reactive transport theories that are applicable to aquifers;
3. apply the theories and methods to field cases in collaboration with societal and industrial partners.
Work performed since the beginning of the project
Flow imaging: While the main focus of research over the last 20 years has been placed on the inversion of piezometric level variations (e.g. Franssen et al., 2009), I have investigated the information that can be obtained from new types of data, with a special emphasis on temperature profiles and radar imaging methods.
Mixing and reactive transport effective modelling: The main effort in the first part of the project has been to quantify the mixing of chemical elements in heterogeneous flows. This is motivated by the lack of fully validated theoretical framework for predicting mixing in porous media, which controls the effective kinetics of chemical reactions (Dentz et al., 2011).
Experiments and observations:
In order to test the applicability of theoretical frameworks, I have designed new experiments based on reactive and non-reactive tracer tests and applied at the Ploemeur experimental site, which belongs to the national network of hydrogeological sites H+ (hplus.ore.fr).
Main results achieved so far
Flow imaging
Novel methodologies have been developed for obtaining detailed characterisation of the flow organisation in heterogeneous media. We have shown that temperature profiles can be interpreted to derive precise flow profiles, which inform on the flow heterogeneity and connectivity properties (Klepikova et al., 2011). Based on collaboration with the University of Lausanne, we have developed a method based on radar imaging of saline tracer to obtain images on the flow paths in between wells (Dorn et al., 2011). This is one of the few methods that allow imaging the flow properties in situ in between boreholes, thus providing critical information on the flow organisation.
Effective modelling of mixing and reactive transport
In collaboration with UPC Barcelona, I have shown the occurrence of anomalous 'non-Fickian' mixing properties in heterogeneous porous media (Le Borgne et al., 2010, Le Borgne et al., 2011). Furthermore, we have investigated the consequences of anomalous mixing properties on effective reaction kinetics (Bolster et al., 2010, de Anna et al., 2011).
Experiments and observations
In order to test the practical applicability of effective transport models, we have conducted a series of novel tracer experiments, using both non-reactive and reactive tracers. About 15 tracer tests were conducted on the fractured rock experimental site of Ploemeur, where we have obtained a characterisation of the flow heterogeneity (part 1). The tracer tests data, obtained under different flow configurations (symmetric and asymmetric dipole, push-pull), constitute a unique database to test dispersion and mixing models. A manuscript presenting the data and analysis is currently under preparation in collaboration with MIT (Kang et al., in preparation). In parallel, reactive transport experiments have been performed to assess the in situ kinetics of denitrification (Boisson et al., in preparation).
Expected final results and their potential impact and use
The expected final result is the development of realistic predictive models for transport and effective reaction kinetics, based on theoretical investigations and validated from experimental data. The effective modelling of dispersion, reaction and speciation of anthropogenic contaminants released by both point and diffuse sources to the soil-aquifer environment is key for assessing and quantifying anthropogenic impacts on groundwater systems and soil/aquifer quality, in the framework of sustainable exploitation.
It has become increasingly apparent over the last 20 to 30 years that European groundwater resources are at risk from a wide variety of stresses including point and diffuse sources of contamination, over-abstraction and saline intrusion. In fact, the problem of a ready supply of clean water for all is global and regarded as one of the biggest challenges of the 21st century (Intergovernmental panel on climate change (IPCC) report 2007). In Europe, these issues are addressed through the Water Framework Directive (WFD) established in 2000 and the Groundwater Directive (GWD) established in 2007, the overall the aim of which is to promote sustainable water use based on long term protection of water bodies in a single management system. These directives fundamentally change the way in which the water industry has operated up to now, presenting both the research and industrial communities with challenging work.
The REACTIVEFLOWS project aims at tackling more specifically the issue of the transport of contaminants in groundwater. The latter is determined by the multi-scale organisation of natural flows (Gelhar, 1993). This complex organisation, due to the existence of heterogeneous geological structures, generally leads to anomalous transport features, such as early or late arrival times and non-Gaussian spatial distributions (Berkowitz et al., 2006). Accounting for these properties is particularly critical for the prediction of contaminant transport in the subsurface. A number of approaches have been developed recently, such as Continuous time random walk (CTRW) theory and fractional Fokker-Planck equations to describe anomalous transport. However, the role of the local flow organisation on effective transport is not yet understood quantitatively (see review of Neuman and Tartakovsky, 2008). When chemical reactions take place, such as dissolution, precipitation, sorption or reactions between aqueous species with possible biological activity, the effect of the flow heterogeneity is even more critical and is not accounted for in most existing theories, which represent a severe limitation of our predictive capabilities (Dentz et al., 2011).
Project objectives
The main objective of the REACTIVEFLOWS project is to establish the link between the characterisation of the flow heterogeneity and the prediction of reactive transport in aquifers. The research methodology is organised into three main goals:
1. develop inverse methods for flow imaging in natural media from geophysical, flow and tracer measurements;
2.quantify the role of the flow organisation on the mixing properties and on the reaction rates, and thus develop reactive transport theories that are applicable to aquifers;
3. apply the theories and methods to field cases in collaboration with societal and industrial partners.
Work performed since the beginning of the project
Flow imaging: While the main focus of research over the last 20 years has been placed on the inversion of piezometric level variations (e.g. Franssen et al., 2009), I have investigated the information that can be obtained from new types of data, with a special emphasis on temperature profiles and radar imaging methods.
Mixing and reactive transport effective modelling: The main effort in the first part of the project has been to quantify the mixing of chemical elements in heterogeneous flows. This is motivated by the lack of fully validated theoretical framework for predicting mixing in porous media, which controls the effective kinetics of chemical reactions (Dentz et al., 2011).
Experiments and observations:
In order to test the applicability of theoretical frameworks, I have designed new experiments based on reactive and non-reactive tracer tests and applied at the Ploemeur experimental site, which belongs to the national network of hydrogeological sites H+ (hplus.ore.fr).
Main results achieved so far
Flow imaging
Novel methodologies have been developed for obtaining detailed characterisation of the flow organisation in heterogeneous media. We have shown that temperature profiles can be interpreted to derive precise flow profiles, which inform on the flow heterogeneity and connectivity properties (Klepikova et al., 2011). Based on collaboration with the University of Lausanne, we have developed a method based on radar imaging of saline tracer to obtain images on the flow paths in between wells (Dorn et al., 2011). This is one of the few methods that allow imaging the flow properties in situ in between boreholes, thus providing critical information on the flow organisation.
Effective modelling of mixing and reactive transport
In collaboration with UPC Barcelona, I have shown the occurrence of anomalous 'non-Fickian' mixing properties in heterogeneous porous media (Le Borgne et al., 2010, Le Borgne et al., 2011). Furthermore, we have investigated the consequences of anomalous mixing properties on effective reaction kinetics (Bolster et al., 2010, de Anna et al., 2011).
Experiments and observations
In order to test the practical applicability of effective transport models, we have conducted a series of novel tracer experiments, using both non-reactive and reactive tracers. About 15 tracer tests were conducted on the fractured rock experimental site of Ploemeur, where we have obtained a characterisation of the flow heterogeneity (part 1). The tracer tests data, obtained under different flow configurations (symmetric and asymmetric dipole, push-pull), constitute a unique database to test dispersion and mixing models. A manuscript presenting the data and analysis is currently under preparation in collaboration with MIT (Kang et al., in preparation). In parallel, reactive transport experiments have been performed to assess the in situ kinetics of denitrification (Boisson et al., in preparation).
Expected final results and their potential impact and use
The expected final result is the development of realistic predictive models for transport and effective reaction kinetics, based on theoretical investigations and validated from experimental data. The effective modelling of dispersion, reaction and speciation of anthropogenic contaminants released by both point and diffuse sources to the soil-aquifer environment is key for assessing and quantifying anthropogenic impacts on groundwater systems and soil/aquifer quality, in the framework of sustainable exploitation.
