Application of multivariate geostatistical methods and risk indexes to identify dump sites and assess risks in historical mining areas.

Abstract

Historical mining areas can lead to long-term soil and water contamination, necessitating their delineation, characterization, and environmental risk assessment. This study utilized a combination of environmental forensic tools (geospatial and statistical analysis techniques) along with a fairly set of standardized risk indices to find the exact location of the old mining waste dumps existing in a historical Pb/Ag mining area and to assess the current environmental risk derived from it. The results indicated that Pb is the most prevalent potentially toxic element, with concentrations significantly exceeding regional background levels. Zn and Cu also exhibited high concentrations, while Ag levels were relatively low. Principal component analysis (PCA) identified six factors associating different metals with geochemical background and mining activities. Several pollution risk indices were employed to evaluate environmental hazards. Pb posed the highest risk, with approximately 75% of samples falling into high-risk categories based on total concentrations (Geoaccumulation Index and Enrichment Factor). Other metals such as Cd, Zn and Cu displayed varying risk levels, whereas Ag posed minimal risk. The Pollution Loading Index (PLI) indicated that around half of samples were highly polluted. However, indices considering bioavailable metals (Risk Assessment Code, RAC) suggested a much lower risk, with only Cd showing moderate risk in 11.1% of samples; the relatively abundant vegetation in the area seems to provide additional evidence for this last consideration. The spatial distribution of sample types, combined with risk indices maps and photogrammetry, facilitated the creation of a 3D map of potential old mining waste dumps using reasonable time work and costs. That integration of techniques and data, together with the great antiquity of some mining activities conducted in the studied area, constitute the main novelty of this work.