Impact of spatial variability in hydraulic parameters on plume migration within unsaturated surficial formations

Abstract

Heterogeneities in textural properties of surficial formations at field scale resuit in spatial variations in hydraulic parameters governing unsaturated zone flow. This study aims at quantifying the influence of such variations on soluté transport resulting from a localized source of radioactive contaminant at ground level. The study focuses on three hydraulic parameters related to the Mualemvan Genuchten formalism, namely the saturated hydraulic conductivity K4, the parameter a inversely proportional to the air-entry value, and the parameter n related to the pore-size distribution. Sets of random fields accounting for spatial variability of these parameters are generated using lognormal dis tributions with different variances and corrélation lengths. These random fields are used as inputs to an unsaturated flow and transport model to simulate radionuclide plume migration.

Combining geostatistics and simulations of flow and transport to characterize contamination within the unsaturated zone

“…Spatial variability of MvG parameters is generally poorly characterised at field scale even if it can signifieantly affect the évolution of contaminant plumes within the unsaturated zone (Pannecoucke et al, 2019). For exam ple, in this study, the tritium plumes simulated using a similar groundwater flow and transport model but various MvG parameter fields (generated from observations of texture sampled in 8 boreholes) are significantly different: their surfaces range from 60 to 150 m2 and their mass centers are spread…”

“…Experimental variograms are computed from i i these values of MvG parameters, which are then interpolated by means of a conditional simulation tool considering variogram models with randomised parameters (Appendix 2). Normal distributions of Br and and lognormal distributions of Ks, a and n are considered(e,p,, Botros et al, 2009;Pannecoucke et al, 2019), with means and variances given by the values of hydraulic parameters at sampled locations. It results in 1,000 sets of 5 random fields.…”

Combining geostatistics and physically-based simulations to characterize contaminated soils

“…Such simulations take into account complex processes governing contamination spread but they require a relevant definition of initial and boundary conditions, as well as internal hydraulic properties. Within the unsaturated zone, the inference of these hydraulic properties is difficult, timeconsuming and the induced uncertainties result in a lack of accuracy in the characterization of the contaminated areas ( [7]).…”

Estimations of hydrodynamical parameters of Fontainebleau sands using GPR monitoring of water infiltrations

“…Hydrodynamic properties of soils is a key knowledge for developing hydrogeological models to many applications such as following the evolution of pollution plumes (Pannecoucke et al, 2019). These properties can be defined using the water retention curve Ө(h) as well as the hydraulic conductivity curve K(h), representing respectively the relationship between the volume water content of the soil, Ө, or the hydraulic conductivity of the soil, K, as a function of suction h. These two curves are usually modeled using the Mualem (1976) -van Genuchten (1980 formalism, valid on a wide variety of soils, using 5 parameters.…”