Hydrogeochemical modeling of geogenic and anthropogenic processes using VISHMOD and integration of geophysical-geological analysis in a Tectonostratigraphic Terrain

The evolution of groundwater flow in hard-rock crystalline aquifers, composed of metamorphic rocks overlain by a thin alluvial fill, is influenced by mixing processes, rock-water interactions, and anthropogenic contamination. This study proposes a comprehensive methodology that combines hydrogeochemical modelling, resistivity geophysical techniques, and detailed geological verification, with the objective of identifying the main processes occurring in these complex geological environments. The results show mixing of different origins associated with three types of groundwater flow and rock-water interactions. These processes include redox reactions, nitrification, and denitrification, the latter of which is linked to anthropogenic sources. These processes are identified in isoresistive hydrogeological units, with resistivity values ranging from 15 to 300 Ohm.m, associated with weathered fractured metamorphic rocks and saturated fractured andesitic rocks. Structural patterns of faults and fractures favour water flow, promoting the occurrence of the various processes identified. This research contributes to the understanding of hydrogeological behaviour in aquifers with metamorphic basements and complex tectonic conditions. It provides a replicable methodology for evaluating water quality at sites with similar geological characteristics.