Geography of soil contamination for characterization and precision remediation of potentially contaminated sites

One of the fundamental problems experienced when evaluations are required (e.g. for reclamation, phytoremediation, containment, etc.) on agricultural or industrial contaminated sites is the geospatial variability of pollutants. The general lack of ex-ante information on type, quantity, and location of potentially hazardous substances requires the use of proper investigation tools to identify their spatial distribution. In this work we focused on developing and applying an integrated approach based on the following steps: i) preliminary investigations (analysis of aerial photos from different periods of time); ii) indirect investigations (by geophysical and spectrometric methods such as ARP, DUAL-EM, Profiler, Gamma-ray and X-ray fluorescence); iii) direct investigations (pedological and micromorphological); iv) stochastic modelling and critical risk of chemical concentrations being exceeded. The investigated area is located in the region of Campania (south-ern Italy), close to the main regional volcanic districts (Phlegraean Fields and Somma-Vesuvius). Maps of the apparent electrical resistivity and conductivity, as well as that of the gamma-ray dose, were obtained for the site in question. On analysing the maps, a good correspondence was found among the outputs obtained from measurements at depths between 0 and 2 m, with a spatial resolution that is slightly better for ARP. The procedure of Normalized Sum of Relative Differences on Geophysical Covariates (NSRDGC) was applied to the 15 maps in order to obtain an integrated variability map of all the surveyed anomalies using the proximal sensors. The resulting map identified the most homogeneous areas where five soil profiles and eight trenches were dug. Field morphological observations enabled three different types of anthropogenic materials enriched in Cr and Zn to be identified. According to their morphology in depth, these materials were not emplaced in a single event. Earth movement and landfilling were carried out at several times in the same area, where a mix of contaminated materials and natural soil is found in the first metre, whereas organic materials are visible separately, probably as a consequence of separate excavations and landfill. Soil micromorphology observations evidenced the presence of Cr-enriched organic materials and secondary crystalline gypsum minerals as well as organic matter coatings inside pores. Such observations suggest the possible fate of some contaminants, highlighting soil mineral and organic associations, as well as the presence of pedofeatures indicating downward movement of colloidal materials.