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Environmental assessment of urban soils and recycled materials

Environmental assessment of urban soils and recycled materials

Challenges

Often considered as an inert material when they support buildings or considered as waste when they are polluted, urban soils are ecosystems in their own right that perform many functions: support for planting in green spaces, support for the development of urban agriculture and gardening, storage of rainwater and carbon, pollution filtering when implementing sustainable drainage systems, support for leisure or mobility infrastructures, etc.

When the existing soil does not have the properties required to perform these functions, the traditional solution is to use natural aggregates and reported agricultural land. Obviously, this approach is not sustainable and proposals are being made to build soils from recycled materials. The new uses of existing and constructed soils raise some questions: can they ensure sufficient and healthy food production? What alternative materials to topsoil can be used to create green spaces? Will urban water infiltration techniques, or the use of treated wastewater for watering or washing public spaces, lead to a deterioration in soil and groundwater quality?

The answer these questions, the quality of soils and materials has to be assessed in relation with their physical and chemical properties and their current and expected functions. It is also of paramount importance to study how to preserve the quality of soils in order to ensure the sustainability of the services they provide.

Scientific goals

The scientific objectives of this research theme are:

Assessment of soil quality and recycled materials

►Characterization of chemical heterogeneity in situ and in the laboratory: semi-quantification of chemical elements by portable X-ray fluorescence spectroscopy, major, trace and ultra-trace elements analysis (ICP-OES, ICP-MS), granulochemistry, contamination mapping

Current focus:

- platinoids (platinum, palladium, rhodium) at emission and in the water-ground-plant system

- fast detection and analysis of mercury in the urban environment

►Physical and hydrodynamic characterization of soils: in-situ and laboratory measurements of infiltration capacity, determination of hydrodynamic parameters by modelling

 

Reactivity of solid phases and their interactions with pollutants

►Characterization of the solid phases of soils and materials and of the phases carrying pollutants by microscopic observation and micro-analysis (X-ray microfluorescence, SEM-EDX probe, DRX, MET) (collaboration agreement with Institut des Matériaux de Nantes)

►Evaluation of pollutant mobility: selective and sequential extraction, batch and column leaching experiments, microanalysis of pollutants in particulate form (colloids)

Focus: platform for observation and microanalysis of soils and materials

Water and pollutant transfers

►Water flow in heterogeneous porous media: non-reactive tracing on model systems (macroporous laboratory column, pilot facility, real sustainable drainage facility), monitoring of non-reactive transport in columns by nuclear magnetic resonance (in collaboration with laboratoire Navier)

►Pollution transfer in urban soils: experimentation under dynamic conditions: laboratory columns (model media and real soils), monitoring of transfers within infiltration facilities, mobilization of pollutants in particulate form (ultrafiltration, granulometry)

►Numerical modelling of water transfer and reactive transfer (solutes) using existing (Hydrus, Phreeqc) or custom written codes (pore-size scale)



 

Infiltration retention Basin Cheviré - Monitoring of pollutants transfer in the soil

Application areas & partnerships

Currently, our fields of applications are:

- long-term monitoring of the quality of urban soils and groundwater within the framework of the ONEVU (Observatoire Nantais des EnVironnements Urbains) (atmospheric deposition, Prairie de Mauves landfill)

- urban runoff water management, in particular the characterisation of emerging pollution (platinum group elements) and the performance of infiltration facilities

- the construction of soils from recycled materials and waste for urban development (green spaces, transport infrastructure, etc.)

- the differentiated management of the soils of community gardens (in case of pollution)

Within IFSTTAR, researchers working on this topic are involved in projects in geotechnics (GMG/GERS), pavement structure (MIT/MAST), infrastructure environmental impacts (EASE and LTE/AME). They collaborate with the porous media team of Laboratoire Navier (ENPC-Ifsttar, Marne-la-Vallée). They also belong to the French research network in urban hydrology, along with LEESU (ENPC), LEHNA (CNRS-ENTPE, Lyon) and CEREMA.

The LEE is a founding member of a consortium in Région Pays-de-la-Loire on soil pollution which aims to create a scientific centre in western France dedicated to the management of diffuse soil pollution (University of Nantes (LPGN), BRGM, EMN (GEPEA, SUBATECH, LEMNA), Agrocampus Ouest (EPHor, Angers), IFREMER, CSTB). The LEE is also part of the IRSTV and is heavily involved in the "Urban Environment" component of the OSU Nantes, in particular by taking part in the management of the research project POLLUSOLS. Finally, the joint research team between the LEE and EPHor Agrocampus Ouest is strengthening the positioning of the two laboratories in the construction of the "Polluted Soils" cluster in Région Pays-de-la-Loire.

Researchers in the theme are involved in French scientific associations (AllEnvi: Agroecology & Soil group) and European actions (COST 1201 on urban gardens, COST 1206 on urban subsoil). They provide expertise to the Ministry of Ecology (PNUR group (Non-Reusable Used Tyres), expertise on soil artificialisation) and the City of Nantes.