Integrated 3D geostatistical and multivariate analysis of geochemical data for characterization and volume estimation...

The municipality of Solofra (Avellino, Italy) is a major center for the tanning industry, where long-term leather processing has generated significant environmental pressure. An abandoned industrial site used to treat organic tannery waste was found to contain illegally dumped materials. A characterization campaign conducted in 2016 involved drilling 68 boreholes to depths of about 10 m and collecting 235 samples. Concentrations of 16 potentially toxic elements were determined, georeferenced, and visualized in a three-dimensional model. A novel methodological framework combining multivariate statistics and three-dimensional geostatistical modelling was applied. Empirical Bayesian Kriging generated spatial models for individual elements. At the same time, Principal Component Analysis identified the main geochemical associations, distinguishing natural volcanic soil signatures (V, As, and Be) from anthropogenic inputs associated with tanning activities, particularly Cr, Sb, Sn, and Tl. Fuzzy Cluster Analysis applied to PCA scores further delineated two main compositional domains: a widespread cluster of tannery waste mixed with volcanic soils and a second cluster of relatively pure tannery waste enriched in chromium and associated elements. Chromium valence partitioning was inferred under assumed reducing conditions, with the data indicating Cr(VI) below detection limits. The observed correlation with organic matter is consistent with possible retention of Cr(III) via adsorption and organic complexation. However, this pattern should be interpreted as indirect evidence of inferred speciation rather than direct confirmation. The integration of multivariate statistics with three-dimensional modelling enabled reconstruction of the landfill's internal geochemical architecture, providing a powerful tool for identifying contaminant hotspots and supporting targeted investigation and remediation in complex industrial waste sites.