Engineered soils (human-made soils) can provide solutions for the recovery of excavated materials; however, these innovative approaches remain limited and require careful development.The international Future Circular Collider (FCC) study hosted by CERN develops processes with the goal to use excavated materials from the construction of a particle-collider based research infrastructure in the frame of an R&D project called "OpenSkyLab". Part of the project is a platform located on 1 ha of terrain made available by CERN in France to develop standard operating procedures for excavated materials re-use.The project addresses several research questions, including how to recycle low-clay molassic materials while managing the complexity of mixing processes and enhancing microbial activity in cost effective manner; how to promote plant growth while improving pedogenesis; and identify plant species can enhance soil pedogenesis processes and ecosystem functioning.The project includes demonstrative, replicated plots and elevated hedgerows plots. Engineered soils were constructed from molassic materials, heterogenous sedimentary rocks typical of Geneva basin, and amended with 0%, 15%, or 30% compost by volume. These substrates were tested under different vegetation types, including Miscanthus giganteus, Kernza (perennial wheat), pasture mixtures, and annual cover crop mixtures. Innovative mixing techniques incorporating inert clay were evaluated to improve substrate aggregation and homogeneity.After one year of installation, primary results showed that all plant species established successfully except Kernza, which failed to grow. A mixture containing 30% compost and 70% molasse provided good soil cover and good adaptability. Notably, pasture mixtures with 15% compost (~1.5 % organic matter) exhibited strong development, better macrofauna integration, and improved soil structure compared with other plots. These findings contribute to the development of processes for the engineered soil-based recovery of molasse excavated from the FCC and other large-scale construction projects.

Constructing soils from waste materials offers a transformative strategy for advancing circular economy objectives by reducing dependency on natural topsoil and minimizing landfill disposal. This study introduces an innovative approach to Technosol construction by incorporating reactive clay-rich materials designed to enhance aggregate structural stability during early soil genesis. Soil production was obtained at pilot-scale thanks to a pelletization device, using varying proportions of excavated earth (60 to 90%), thermal mud containing reactive clays (0 to 10%) and mature compost (10 to 30%). 9 plots of 9 m² each were established with the mixtures and planted with grass. Aggregate stability was assessed after 7 months through particle size distribution, mean weight diameter (MWD), and resistance to wetting and simulated rainfall. Results revealed that compost and plant growth significantly stimulated aggregate development. Stability was optimized in mixtures containing 30% compost with 10% thermal mud and 20% compost with 5% thermal mud, particularly under slow wetting and mechanical stress conditions that commonly occur during rainfall events. In contrast, high clay content without adequate compost led to the production of fine particles smaller than 50 µm, surface sealing, and reduced aggregate stability. These findings provide new insights into the role of reactive clays within engineered soil systems, demonstrating that appropriately balanced mineral–organic mixtures can promote the formation of structurally resilient Technosols suitable for sustainable field-scale application.

Clay minerals play a crucial role in regulating the structure and functions of soils because of their chemical nature and their interactions with other soil constituents. In this context, a key objective of the research described in this article was to assess the extent to which the addition of various types of recycled clay-rich materials to soils prone to crusting and erosion increase their clay content and improve their physical properties. Excavated soil (ExS), considered waste under European Union law, and quarry sludge (QS), an industrial by-product of the washing process in mining operations, were used as soil amendments. ExS is dominated by swelling clay mineralogy such as interstratified illite-smectite, whereas QS contains high level of non-swelling clay minerals such as kaolinite and illite, and a low level of interstratified illite-smectite. Lysimeters were filled with topsoil (0-30 cm) from an agricultural field. Treatments where the soil was amended with these materials were compared with a control without amendment. Lettuce was cultivated for three growing seasons. After 250-days, the aggregate stability and water retention of the topsoil were measured. The equivalent pore-size distribution (PSD), derived from the soil water retention curve, was analysed to predict soil water and aeration status. The application of QS to the topsoil enhanced soil structure without compromising lettuce productivity compared with the control and other treatments. However, amending topsoil with ExS decreased the stability because of the abundance of swelling clay minerals. Soil water retention at saturation increased from 27% in the control to 42% and 36% with ExS and QS amendments, respectively. At a pressure head >15,000 cm (residual pores <0.2 mu m), water retention rose from 6% in the control to 19% with ExS and 14% with QS. The application of the clay-rich material increased small pores compared with larger ones. This led to a minor increase in porosity responsible for water movement, aeration and root growth. This observation highlights the limitations of clay application benefits, which depend on the quantity and mineralogy of the clay and the presence of other binding agents. Further research is needed to investigate the combined effects of organic matter and clay-rich materials on improving the soil structure and optimizing the pore size distribution for multiple functions.

Purpose The EU Water Framework Directive (European Union Off J Eur Comm 2000) and EU Waste Framework Directive (European Union Off J Euro Union 2008) impacted the Beneficial Use (BU) of sediments in Europe. INTERREG has supported initiatives to change the perception that sediments are a waste. In this paper we provide an overview of tools, pilot sites and measuring techniques developed and used for the BU of sediments within seven European Union INTERREG projects. We illustrate the lessons learned regarding barriers and enablers for BU of sediments.Materials and methods BU of sediments is a combination of factors. The following aspects are considered. The sediment must be suitable for use and be in engineering compliance. The sediment must also need to meet the end of waste criteria, as well as to be in environmental compliance. To check in the field if engineering and environmental compliance is feasible, on-site analyses and decision support tools are needed. When BU use is possible, there must be a benefit, either in an added socio-economic value or in ecosystem services. To define benefits the impact of Business as Usual (BAU) should also be expressed. Stakeholder perception and spatial restraints determine areas for BU of sediments with spatial consensus.Results and discussion The pilots and case studies described in this paper are examples of different applications of BU of sediments in northwest Europe. The tools, equipment, pilot tests and on-site monitoring techniques developed by the identified INTERREG projects are useful as BU enablers, for both citizens (an enabler is what is in it for me versus a barrier like residents opposing to proposed developments in their local area or the Not In My Back Yard (NIMBY) principle), and for regulators (what are the risks versus benefits as compared to BAU).Conclusions The main barriers for beneficial use of sediments are the social acceptance when sediments are used on land (often seen as waste disposal) and the extra direct cost versus the cost for disposal, while indirect benefits such as the potential for nature development, the impact on Gross Domestic Product (GDP) or more locally on the extra jobs created, are generally not considered. Also, the impact of BAU is often not explicitly considered.

While risk-based contaminated land management is an essential component of sustainable remediation, uncertainty is an unavoidable aspect of risk assessment, since most of the parameters that influence risk are typically affected by uncertainty. Uncertainty may be of different origins; i.e., stochastic or epistemic. Stochastic (or aleatoric) uncertainty arises from random variability related to natural processes, while epistemic uncertainty arises from the incomplete/imprecise nature of available information. But the latter is rarely considered in risk assessments, with the result that risk-based soil quality objectives are almost invariably presented as precise (unique) threshold values. In this paper it is shown: (i) how the joint treatment of stochastic and epistemic uncertainty in risk assessment can lead to soil quality objectives presented as intervals rather than precise values and (ii) how this provides an upper risk-based safeguard for post-remediation monitoring values. The proposed method is illustrated by a real case of soils contaminated by arsenic located in the North-East of France. At this site steel manufacturers have gradually filled up a small valley with slag and dust, over more than a century. These materials are enriched in various metal(loid)s, including arsenic and lead. As the environmental authority has asked for a conversion of the site to other uses that may involve access by the general public, an investigation of human health risk was performed based on a sampling campaign and chemical characterizations including various types of extractions and an analysis of bioaccessibility. While further investigations are required to improve the bioaccessibility model, the human health risk presented herein shows how partial or imprecise information can be incorporated in the analysis while taking into account underlying uncertainties.

Permanganate is an oxidant usually applied for in situ soil remediation due to its persistence underground. It has already shown great efficiency for dense nonaqueous phase liquid (DNAPL) degradation under batch experiment conditions. In the present study, experimental permanganate oxidation of a DNAPL - coal tar - sampled in the groundwater of a former coking plant was carried out in a glass bead column. Several glass bead columns were spiked with coal tar using the drainage-imbibition method to mimic on-site pollution spread at residual saturation as best as possible. The leaching of organic pollutants was monitored as the columns were flushed by successive sequences: successive injections of hot water, permanganate solution for oxidation, and ambient temperature water, completed by two injections of a tracer before and after oxidation. Sixteen conventional US-EPA PAHs and selected polar PACs were analyzed in the DNAPL remaining in the columns at the end of the experiment and in the particles collected at several steps of the flushing sequences. Permanganate oxidation of the pollutants was rapidly limited by interfacial aging of the DNAPL drops. Moreover, at the applied flow rate chosen to be representative of in situ injections and groundwater velocities, the reaction time was not sufficient to reach high degradation yields but induced the formation and the leaching of oxygenated PACs.

Reclamation measurements are commonly applied to mitigate the leaching of metal pollutants in order to reduce the risk for humans and the environment. The stabilization of mine tailings can be performed by amending with organic or inorganic materials. In a recent laboratory microcosm experiment (Thouin et al., 2019), the addition of a mining slurry called ochre and manure, either alone or in combination, drastically reduced the leaching of several metal pollutants, notably Pb. Nevertheless, the biogeochemical processes involved in the immobilization of metal pollutants remain unknown, preventing the management of this remediation technique from being optimized and its extension to other sites. To fill this gap, a multicomponent mixing model was developed to simulate and forecast the impact of amendments on the leaching of metal pollutants. This model accounts for the following biogeochemical processes: kinetically-controlled dissolution/precipitation reactions, sorption reactions (i.e. surface complexation reactions), water-gas interactions and microbial respiration with an explicit microbial growth. For all treatments, simulations revealed that Pb reactivity followed dynamic patterns driven by watering steps. The decrease in Pb concentration in the leachates of amended tailings compared to untreated tailings was also accurately reproduced. In untreated tailings, Pb reactivity is mainly controlled by the dissolution of Pb-bearing mineral phases. These reactions were maintained in thermodynamic disequilibrium due to the renewal of pore solution at each watering step. In amended tailings, this pattern was strengthened as the iron oxides contributed by ochre maintained a low Pb concentration in pore solution by sorbing released Pb. Sorption reactions were enhanced by the increase in pH induced by the dissolution of calcium carbonate initially present in ochre. The latter reaction was partially counterbalanced in tailings amended with manure as organic matter provided sufficient energy to fuel microbial aerobic respiration, leading to the release of protons. Pb desorption was promoted by this pH drop. The magnitude of these reactions was not strictly proportional to the amount of manure added. For 0.15% by weight, aerobic respiration did not occur whereas its yield was similar for 1% and 2%. By providing a better understanding of the effect of amendment, this multicomponent mixing model is a powerful tool to optimize the reclamation of tailings, in order to limit contaminant transfer to the environment.

Reclamation measurements are commonly applied to mitigate the leaching of metal pollutants in order to reduce the risk for humans and the environment. Organic and/or inorganic amendments are often recommended to stabilize tailings and to reduce leaching of contaminants. In a recent microcosm percolation experiment (Thouin et al., 2019), the addition of a mining slurry called ochre and manure, either alone or in combination, drastically reduced the leaching of several metal pollutants, notably Pb. Nevertheless, the biogeochemical processes involved in the immobilization of metal pollutants remain unknown, preventing the management of this remediation technique from being optimized and its extension to other sites. To fill this gap, a multicomponent reactive model was developed to simulate and forecast the impact of amendments on the leaching of metal pollutants. This model accounts for the following biogeochemical processes: kinetically-controlled dissolution and precipitation reactions, sorption reactions (i.e. surface complexation reactions), water-gas interactions and microbially-driven redox reactions with an explicit microbial growth. For all treatments, simulations revealed that Pb reactivity followed dynamic patterns driven by watering steps. The decrease in Pb concentration in the leachates of amended tailings compared to untreated tailings was also accurately reproduced. In untreated tailings, Pb reactivity is mainly controlled by the dissolution of Pb-bearing mineral phases. These reactions were maintained in thermodynamic disequilibrium due to the renewal of pore solution at each watering step. In amended tailings, this pattern was strengthened as the iron oxides contributed by ochre maintained a low Pb concentration in pore solution by sorbing released Pb. Sorption reactions were enhanced by the increase in pH induced by the dissolution of calcium carbonate initially present in ochre. The latter reaction was partially counterbalanced in tailings amended with manure as organic matter provided sufficient energy to fuel microbial aerobic respiration, leading to the release of protons. Pb desorption was promoted by this pH drop. By providing a better understanding of the effect of amendment, this multicomponent reactive model is a powerful tool to optimize the reclamation of tailings, in order to limit contaminant transfer to the environment. Thouin H. et al. (2019), Appl. Geochem. 111, 104438

Manganese (Mn) oxides are ubiquitous in the environment, being found for example under the form of coatings and nodules in soils, freshwater and marine sediments, and as rock varnishes in temperate, arid, and polar areas. In all these settings, they frequently control or influence the geochemical cycle of many trace elements, including metals and organics, through sorption and oxidative degradation mechanisms. In addition, Mn oxides can be used for soil remediation processes, by taking advantage of their exceptional reactivity. This chapter is divided in two main sections. The first section is devoted to reviewing the nature of Mn oxides found in pristine natural settings. A specific effort made to distinguish between layered and tunnel structures, and their genetic relationship is discussed. Their reactivity toward metals and organics and the evolution of this reactivity as a function of time and chemical conditions are also discussed. In particular, the short- and long-term metal immobilization processes are reviewed. Considering that the associations observed in natural settings can be considered as representative of those occurring during long-term interaction between Mn oxides and the element of interest, the first section provides insights about the long-term retention capacities of Mn oxides as well as the nature of the products formed during the reaction of Mn oxides and metals or organics. The second section of this chapter focuses on the potential uses of Mn oxides for soil remediation. Mn oxides can be used as (1) oxidative reagents for organic and inorganic substances, (2) sorption mediums of trace metals and metalloids, and (3) reactive sorbent agents for chemical warfare agent and organophosphate pesticides. Efficiencies of each technique are variables and specific care is needed regarding the degradation products in the case of organic substances remediation. The use of both natural and engineered Mn oxides is referenced for soil remediation. Birnessite-like structures seem to be the most efficient Mn oxides for cleanup purposes.

In situ chemical oxidations are known to remediate PAH contaminations in groundwater and soils. In this study, batch-scale oxidations aim to compare the PAC (polycyclic aromatic compound) degradation of three oxidation processes traditionally applied for soil treatment: permanganate, heat-activated persulfate (60 °C) and Fenton-like activated by magnetite, to results obtained with ferrates (FeVI). Widely studied for water treatments, ferrates are efficient on a wide range of pollutants with the advantage of producing nontoxic ferric sludge after reaction. However, fewer works focus on their action on soil, especially on semi-industrial grade ferrates (compatible with field application). Oxidations were carried out on sand spiked with dense non-aqueous phase liquid (DNAPL) sampled in the groundwater of a former coking plant. Conventional 16 US-EPA PAHs and polar PACs were monitored, especially potential oxygenated by-products that can be more harmful than parent-PAHs. After seven reaction days, only the Fenton-like showed limited degradation. Highest efficiencies were obtained for heat-activated persulfate with no O-PAC ketones formed. Permanganate gave important degradation, but ketones were generated in large amount. The tested ferrates not only gave slightly lower yields due to their auto-decomposition but also induced O-PAC ketone production, suggesting a reactional pathway dominated by oxidoreductive electron transfer, rather than a radical one.

This chapter highlights the complexity of water and chemical phenomena that control the behaviour of contaminants in the unsaturated zone (UZ). Numerous mechanisms are involved in fixing these elements in soils, and many are not fully understood. This area of study is characterised by their hierarchy, or the predominance of one mechanism over another, depending on the bio-physico-chemical conditions of the environment. Understanding this hierarchy requires site analysis and measurements which currently are not always carried out. Nevertheless, estimating the potential risk of a moderately contaminated site in the medium and long term, determining its future use, predicting groundwater quality and optimally managing contaminated excavated material (waste and polluted soil) all require a good understanding of pollutant behaviour in time and space.

It is now certain that soil evolution will be strongly influenced by climate change. In particular, young soils, such as anthropogenic soils, show evolution patterns that change faster than natural soils. They can contain large quantities of organic pollutants (in the context of industrial activities) which mobility in the environment might differ under the impact of several environmental factors, particularly climate. To better quantify the link between climatic fluctuations and their impact on soil properties, it is important to understand how meteorological records can be derived into pedoclimates. Using HYDRUS-1D, we converted fluctuations of water content and temperature into pedoclimatic events over time as a function of climatic conditions, soil properties and depth. First, using data collected from lysimeters and a local weather station, we calibrated the fluctuations in soil water content and soil temperature. The model efficiently predicts the evolution of soil temperature (index of agreement >0.97 and RMSE <1.8°C) with a simple convection-dispersion equation. Regarding water content, empirically-estimated hydraulic properties were slightly satisfactory compared to inverse-solution obtained parameters. In a second step, we used the pedoclimate simulated from 10-year datasets collected from 6 global weather stations (Nancy - Nantes - Marseille – France, Darwin – Australia, Denver – USA and Helsinki – Finland) to estimate the occurrences of freeze-thaw cycles (FTC), wetting-drying cycles (WDC), the temperature regimes and the number of days when the soil temperature rose above 28°C. The frequency of occurrence of pedoclimatic events decreased with depth and was strongly controlled by climate type. The developed transcription calculus could potentially be used to predict the evolution over time of Technosol properties, such as the fate of the organic matter or organic pollutants under different climatic conditions.