Development of a probability approach to determine water and colloidal pollutant flow behavior in urban heterogeneous soils

Nature-based systems are being employed to allow stormwater to infiltrate directly in the soil, which is supposed to capture pollutants. To better track the evolution of such systems performances, in particular the infiltration and filtration performances, and to be able to optimize their management, these systems need to be better known. Currently, there is a lack of knowledge and methods regarding the characterization of the macropores and matrix contributions in infiltration and filtration of urban soils, whereas the quality of groundwater and the capacities of these systems are at stake. To tackle these limits, a large infiltrometer of 50 cm in diameter with two water-supply reservoirs of approximately 40 L each, was developed to characterize both hydrodynamic and nanotracers transfer parameters. Cumulative water infiltration was carried out at a constant hydraulic pressure head of 10 cm. Superparamagnetic iron oxide nanoparticles (SPIONs), which mimic both colloidal pollutants and bacteria flow behaviors in soils, were designed to be detectable by ground-penetrating radar (GPR). Fifty volumes of SPIONs solution (i.e., 50 x 5 mL at 3.35g/L) were injected into the ring and the GPR was passed along different survey lines around the ring several times during the infiltration experiment. GPR data was treated with ReflexW (Sandmeier Scientific Software, Karlsruhe, Germany) and Rockware (RockWare, Inc, 2015) to define a 3D block diagram of the infiltration bulb. The probability of presence of the nanoparticles was obtained from comparing the radargrams, before and after nanoparticle injection, by using two methods (Allroggen and Tronicke, 2015; Di Prima et al., 2020) on a R software (https://www.R-project.org/).The large infiltrometer device, compared with a smaller one (Di Prima et al., 2015), is proved effective for estimating water and transfer parameters. The dispersion of SPIONs gave an idea of the relative importance of the transfer through the soil macropores as compared to the soil matrix. The probability of SPIONs presence gave information on the filtration function of soils. The whole device application will be illustrated and discussed with regard to its use for the assessment of the infiltration and filtration functions of bio-infiltration systems. Allroggen, N., Tronicke, J., 2015. Attribute-based analysis of time-lapse ground-penetrating radar data. Geophysics 81, H1–H8. https://doi.org/10.1190/geo2015-0171.1Di Prima, S., Lassabatere, L., Bagarello, V., Iovino, M., Angulo-Jaramillo, R., 2015. Testing a new automated single ring infiltrometer for Beerkan infiltration experiments. Geoderma 262, 20–34. https://doi.org/10.1016/j.geoderma.2015.08.006Di Prima, S., Winiarski, T., Angulo-Jaramillo, R., Stewart, R.D., Castellini, M., Abou Najm, M.R., Ventrella, D., Pirastru, M., Giadrossich, F., Capello, G., Biddoccu, M., Lassabatere, L., 2020. Detecting infiltrated water and preferential flow pathways through time-lapse ground-penetrating radar surveys. Sci. Total Environ. 726, 138511. https://doi.org/10.1016/j.scitotenv.2020.1385