Estimation de la concentration en hydrocarbures totaux du sol d’un ancien site pétrochimique

The exploratory variographic analysis of the total hydrocarbon concentration measurements in the soil of a former petrochemical implant highlighted the heterogeneity of the pollution. The bimodality on the histogram indicated the presence of two classes of concentration, which represented different spatial structures. We showed how a detailed examination of the data could reveal, for example, a local backfill. Cross-validation, which allowed comparison of measured and estimated concentration values at sampling points, was used to demonstrate that taking into account this spatial heterogeneity was necessary to improve estimation accuracy. It also enabled evaluation of uncertainties, particularly in the estimation of high concentrations. Considering the case of a punctual selection, we compared estimated and effective recoverable pollutant quantities and average concentrations across the three models. The analysis quantified the effect of information resulting from inevitable selection errors. A simple and rigorous method for calculating the probability of exceeding threshold levels or local quantiles of the concentration histogram was presented.