Final Report Summary - ADVOCATE (Advancing Sustainable In Situ Remediation for Contaminated Land and Groundwater)
The ADVOCATE project (www.theadvocateproject.eu) delivered innovative in situ remediation concepts and technologies for the sustainable management of contaminated land and groundwater in Europe. This supports EU policy ambitions for sustainable development in Member States and specific legislation, such as the Water Framework Directive, Groundwater Directive and others, developed to protect and improve the quality of soil and groundwater resources in Europe. The objectives of the project were to (i) research innovative processes and techniques for the sustainable remediation of contaminants in situ, (ii) develop process-level understanding and appraise technology concepts at laboratory-scale through to field-scale application, (iii) develop relevant performance assessment methods and tools for engineering design of sustainable in situ remediation processes and technology, and (iv) develop a decision-making framework for the use of in situ remediation in the sustainable development of groundwater resources. The key results, conclusions and achievements arising from the project are integrated in four over-arching categories below.
(1) Process understanding and appraisal
The groundwater-surface water interface (GSI) is an important but poorly understood critical zone of enhanced biodegradation and attenuation for many contaminants in rivers and groundwater. To address this, high intensity spatial-temporal resolution analysis of solute source and water/solute fluxes across the GSI at a catchment-scale has been completed. New models were developed to analyse the kinetics of contaminant degradation in the GSI. Novel methods were used to investigate the time and spatially variable fluxes between river and groundwater, and new algorithms were developed to estimate water fluxes from temperature measurements. The results and techniques developed permit an improved assessment to be made of contaminant transport and attenuation at the GSI for more cost-effective remediation strategies at sites.
New insight has been gained on the role of mixing processes that enhance in situ biodegradation of organic contaminants in plumes. Most biodegradation occurs at the interface ("fringe") between plumes and uncontaminated groundwater, but is limited by the supply of oxidants due to dispersion in the aquifer. Field studies show that a conventional pump and treatment system can be used to enhance the biodegradation of organic contaminants in plumes. This occurs by increasing the flux of dissolved oxidants (via dispersive mixing) into the plume to support biodegradation processes and reducing limitations on microbial activity. It offers regulators and consultants new ways to link engineered and passive remediation measures for sites.
(2) Technology evaluation and development
New in situ monitoring technology (Vadose zone Monitoring System, VMS) has been developed to interpret the transport of vadose zone contaminants to groundwater. The VMS uses sensors installed in vertical and inclined boreholes to capture real-time data on contaminant distribution, soil chemistry and water percolation, as well as surface imaging. It improves understanding of the dynamics between vadose zone recharge and changes in soil water chemistry with depth, time and infiltration. This groundbreaking system was tested at a site in Belgium, offering unrivalled resolution of vadose zone hydraulic and physicochemical properties for contaminant transport analysis. It provides improved conceptual models of vadose zone contaminant fate and transport, better characterisation of processes controlling contaminant migration and more accurate estimates of contaminant flux to groundwater. This technology and the interpretation methodology (see below) enables regulatory bodies to develop improved risk assessment protocols that integrate vadose zone contaminant fate processes and practitioners to design more cost-effective and sustainable monitoring and remediation measures for vadose zone impacts on groundwater.
Novel permeable reactive barrier (PRB) technology using low-cost waste materials (brown coal and compost) has been developed for the in situ treatment of groundwater containing organic chemicals (petroleum hydrocarbons, chlorinated solvents) and heavy metals. The concept has been evaluated with laboratory batch and column treatability studies, supported by numerical modelling, to develop engineering design guidelines for implementation. Pilot-scale PRB installations show excellent performance at the field-scale for the treatment of chlorinated solvent-contaminated groundwater. Other research has developed and optimised constructed wetlands as an ex situ treatment concept to manage ammonium contamination in groundwater. Design guidelines have been developed to implement this treatment technology at the field-scale, using naturally-occurring aerobic and anaerobic biological processes for nitrogen removal. These innovations provide low-cost, environmentally sustainable treatment alternatives to manage a variety of groundwater contaminants in mixtures, for use by engineers, contractors and decision makers in the field.
Microbial fuel cell biotechnology was explored as an approach for the in situ bioremediation of contaminated groundwater. Bench-scale proof-of-concept studies, using a new reactor design, show enhanced removal of organic compounds in groundwater contaminated with phenols. This occurs by overcoming electron acceptor mass transfer limitations, which usually affects in situ bioremediation. These studies demonstrated electricity production coupled to biodegradation of the organic compounds, offering the potential for application at field-scale. However, the complex interactions in the systems need further research before this is possible.
(3) Performance assessment methods
A methodology to integrate surface and cross-borehole geophysical methods for hydrogeological characterisation and imaging of solute transport and contaminant fate in the vadose zone has been devised for use with the VMS (above), and tested at field-scale (WP2 and WP7). The subsurface images provide the spatial coverage needed to characterise subsurface heterogeneities and moisture content distributions with the increased resolution needed to improve numerical analysis of contaminant transport predictions.
Multi-isotope approaches, combined with molecular analysis of microbial community composition, have been developed to advance our understanding of microbial controls on nitrogen removal from ammonium-rich groundwater systems. These dual approaches are able to better interpret in situ biological transformation of nitrogen in groundwater contaminated with ammonium. They have been used to support the design of ex-situ remediation strategies (constructed wetlands) and show variability of in-situ nitrogen removal processes. The findings improve the accuracy of predictive modelling of pollutant fate and transport in systems affected by mixed contaminants and enable stakeholders to make better decisions about sustainable site management.
New dual stable isotope methods, using carbon and chlorine (C-Cl) isotopes, have been developed to evaluate the origin and fate of chlorinated ethenes in groundwater. The extent of C and Cl isotope fractionation due to biodegradation was successfully determined in laboratory studies. Field studies in Switzerland (12 sites) and Denmark showed this versatile methodology can be used to delineate contaminant sources, identify in situ contaminant transformation processes, improve the prediction of contaminant fate based on numerical models, and assess remediation performance. The research also developed a new modelling approach that incorporates C and Cl isotopes as a site assessment tool for field projects. The results are important to many stakeholders, in providing guidance to regulators and consultants on which questions and phase of site management isotope methods are best applied. In addition, the research provides tools for consultants to implement the approach, including analytical and modelling methods.
A simple method-Integrated Spatial Snap-shot Method (ISSM)-has been devised to assess the natural attenuation capacity of rivers, using nitrate as example. It involves the identification of few (<25) monitoring stations at critical points in a catchment and the analysis of fluxes at two contrasting discharge patterns in two extreme seasons. Using water flow, nitrate isotopes and solute fluxes, hotspots of surface water quality and seasonal changes can be deduced. This method is transferrable to catchments in different geographical conditions, as a preliminary catchment-scale study to identify suitable restoration sites in large catchments.
(4) Management and decision-making tools
Existing decision-support tools and sustainability indicators used to evaluate the sustainability of in situ remediation measures were critically examined, using case studies, to identify limitations and weaknesses. The research explored the effect of different sets of sustainability indicators and tool structures on predictions. From this, an improved methodology was developed to integrate land-use efficiency and land-use benefits in a life cycle analysis of brownfield redevelopment alternatives. This novel approach integrates the availability of land for redevelopment in the evaluation of different brownfield remediation strategies.
New integrated groundwater sampling, stable isotope and modelling approaches have been developed to interpret the impact of industrial mega-sites on groundwater quality at a regional-scale. Using a site contaminated with organic and inorganic chemicals, the research established the key controls on contaminant release to groundwater and transport processes in the aquifer, leading to improved conceptual models for more reliable decision making that ensures prioritisation of resources for cost-effective design of monitoring. The research identified key limitations in current monitoring protocols for such sites and how this can be improved for use by stakeholders (site owners and regulators) responsible for site and regional-scale studies.
New analytical stochastic modelling tools were developed to assess the key role of changing flow regimes and climatic patterns in determining the distribution of riparian vegetation along river transects. Probabilistic descriptions of streamflows, based on catchment-scale climate and geomorphological data, are used in the absence of discharge data. This method can predict river flow duration using limited climate and landscape information, for decisions on water resource management, ecological studies and flood risk assessment. When combined with water chemistry data, it can interpret the contaminant attenuation capacity of a river.
(1) Process understanding and appraisal
The groundwater-surface water interface (GSI) is an important but poorly understood critical zone of enhanced biodegradation and attenuation for many contaminants in rivers and groundwater. To address this, high intensity spatial-temporal resolution analysis of solute source and water/solute fluxes across the GSI at a catchment-scale has been completed. New models were developed to analyse the kinetics of contaminant degradation in the GSI. Novel methods were used to investigate the time and spatially variable fluxes between river and groundwater, and new algorithms were developed to estimate water fluxes from temperature measurements. The results and techniques developed permit an improved assessment to be made of contaminant transport and attenuation at the GSI for more cost-effective remediation strategies at sites.
New insight has been gained on the role of mixing processes that enhance in situ biodegradation of organic contaminants in plumes. Most biodegradation occurs at the interface ("fringe") between plumes and uncontaminated groundwater, but is limited by the supply of oxidants due to dispersion in the aquifer. Field studies show that a conventional pump and treatment system can be used to enhance the biodegradation of organic contaminants in plumes. This occurs by increasing the flux of dissolved oxidants (via dispersive mixing) into the plume to support biodegradation processes and reducing limitations on microbial activity. It offers regulators and consultants new ways to link engineered and passive remediation measures for sites.
(2) Technology evaluation and development
New in situ monitoring technology (Vadose zone Monitoring System, VMS) has been developed to interpret the transport of vadose zone contaminants to groundwater. The VMS uses sensors installed in vertical and inclined boreholes to capture real-time data on contaminant distribution, soil chemistry and water percolation, as well as surface imaging. It improves understanding of the dynamics between vadose zone recharge and changes in soil water chemistry with depth, time and infiltration. This groundbreaking system was tested at a site in Belgium, offering unrivalled resolution of vadose zone hydraulic and physicochemical properties for contaminant transport analysis. It provides improved conceptual models of vadose zone contaminant fate and transport, better characterisation of processes controlling contaminant migration and more accurate estimates of contaminant flux to groundwater. This technology and the interpretation methodology (see below) enables regulatory bodies to develop improved risk assessment protocols that integrate vadose zone contaminant fate processes and practitioners to design more cost-effective and sustainable monitoring and remediation measures for vadose zone impacts on groundwater.
Novel permeable reactive barrier (PRB) technology using low-cost waste materials (brown coal and compost) has been developed for the in situ treatment of groundwater containing organic chemicals (petroleum hydrocarbons, chlorinated solvents) and heavy metals. The concept has been evaluated with laboratory batch and column treatability studies, supported by numerical modelling, to develop engineering design guidelines for implementation. Pilot-scale PRB installations show excellent performance at the field-scale for the treatment of chlorinated solvent-contaminated groundwater. Other research has developed and optimised constructed wetlands as an ex situ treatment concept to manage ammonium contamination in groundwater. Design guidelines have been developed to implement this treatment technology at the field-scale, using naturally-occurring aerobic and anaerobic biological processes for nitrogen removal. These innovations provide low-cost, environmentally sustainable treatment alternatives to manage a variety of groundwater contaminants in mixtures, for use by engineers, contractors and decision makers in the field.
Microbial fuel cell biotechnology was explored as an approach for the in situ bioremediation of contaminated groundwater. Bench-scale proof-of-concept studies, using a new reactor design, show enhanced removal of organic compounds in groundwater contaminated with phenols. This occurs by overcoming electron acceptor mass transfer limitations, which usually affects in situ bioremediation. These studies demonstrated electricity production coupled to biodegradation of the organic compounds, offering the potential for application at field-scale. However, the complex interactions in the systems need further research before this is possible.
(3) Performance assessment methods
A methodology to integrate surface and cross-borehole geophysical methods for hydrogeological characterisation and imaging of solute transport and contaminant fate in the vadose zone has been devised for use with the VMS (above), and tested at field-scale (WP2 and WP7). The subsurface images provide the spatial coverage needed to characterise subsurface heterogeneities and moisture content distributions with the increased resolution needed to improve numerical analysis of contaminant transport predictions.
Multi-isotope approaches, combined with molecular analysis of microbial community composition, have been developed to advance our understanding of microbial controls on nitrogen removal from ammonium-rich groundwater systems. These dual approaches are able to better interpret in situ biological transformation of nitrogen in groundwater contaminated with ammonium. They have been used to support the design of ex-situ remediation strategies (constructed wetlands) and show variability of in-situ nitrogen removal processes. The findings improve the accuracy of predictive modelling of pollutant fate and transport in systems affected by mixed contaminants and enable stakeholders to make better decisions about sustainable site management.
New dual stable isotope methods, using carbon and chlorine (C-Cl) isotopes, have been developed to evaluate the origin and fate of chlorinated ethenes in groundwater. The extent of C and Cl isotope fractionation due to biodegradation was successfully determined in laboratory studies. Field studies in Switzerland (12 sites) and Denmark showed this versatile methodology can be used to delineate contaminant sources, identify in situ contaminant transformation processes, improve the prediction of contaminant fate based on numerical models, and assess remediation performance. The research also developed a new modelling approach that incorporates C and Cl isotopes as a site assessment tool for field projects. The results are important to many stakeholders, in providing guidance to regulators and consultants on which questions and phase of site management isotope methods are best applied. In addition, the research provides tools for consultants to implement the approach, including analytical and modelling methods.
A simple method-Integrated Spatial Snap-shot Method (ISSM)-has been devised to assess the natural attenuation capacity of rivers, using nitrate as example. It involves the identification of few (<25) monitoring stations at critical points in a catchment and the analysis of fluxes at two contrasting discharge patterns in two extreme seasons. Using water flow, nitrate isotopes and solute fluxes, hotspots of surface water quality and seasonal changes can be deduced. This method is transferrable to catchments in different geographical conditions, as a preliminary catchment-scale study to identify suitable restoration sites in large catchments.
(4) Management and decision-making tools
Existing decision-support tools and sustainability indicators used to evaluate the sustainability of in situ remediation measures were critically examined, using case studies, to identify limitations and weaknesses. The research explored the effect of different sets of sustainability indicators and tool structures on predictions. From this, an improved methodology was developed to integrate land-use efficiency and land-use benefits in a life cycle analysis of brownfield redevelopment alternatives. This novel approach integrates the availability of land for redevelopment in the evaluation of different brownfield remediation strategies.
New integrated groundwater sampling, stable isotope and modelling approaches have been developed to interpret the impact of industrial mega-sites on groundwater quality at a regional-scale. Using a site contaminated with organic and inorganic chemicals, the research established the key controls on contaminant release to groundwater and transport processes in the aquifer, leading to improved conceptual models for more reliable decision making that ensures prioritisation of resources for cost-effective design of monitoring. The research identified key limitations in current monitoring protocols for such sites and how this can be improved for use by stakeholders (site owners and regulators) responsible for site and regional-scale studies.
New analytical stochastic modelling tools were developed to assess the key role of changing flow regimes and climatic patterns in determining the distribution of riparian vegetation along river transects. Probabilistic descriptions of streamflows, based on catchment-scale climate and geomorphological data, are used in the absence of discharge data. This method can predict river flow duration using limited climate and landscape information, for decisions on water resource management, ecological studies and flood risk assessment. When combined with water chemistry data, it can interpret the contaminant attenuation capacity of a river.