Factorial Kriging for Mapping the Geochemical Background from Gamma Dose Rate Data Downstream of a Former Uranium Mine - 23194

Downstream of former uranium mining sites, the dissemination of radioactively-enriched material from past mining and milling activities may result in increased uranium concentrations, especially along watercourses and in lakes and wetlands. Identifying the potential sources of uranium, i.e., geochemical background versus mining activities, is a key element for the decision-making process, especially for defining the strategies of effective management and remediation of contaminated soils and sediments. In this study, a geostatistical approach is applied for extracting the geochemical background from gamma dose rate data acquired downstream of a former French uranium mining area. The exploratory data analysis shows that the spatial structure of the gamma dose rate consists of two components: a short isotropic component (10 m-range) that corresponds to the geochemical background; and a long anisotropic component (30-60 m-range) that corresponds to the drainage network features previously fed by the mine discharge water. The gamma dose rate on the whole area of interest was simulated by kriging of the measured values and the spatial component related to the geochemical background was then extracted by using factorial kriging. The proportion of the gamma dose rate explained by the geochemical background according to factorial kriging is consistent within uncertainties with geochemical analyses performed on soil and sediment samples. This study thus highlights the potential of such geostatistical approaches for better exploiting radiometric data. (authors)