Hydrogeochemical processes in aquifers of volcano-sedimentary origin using inverse modeling

Abstract

The study area is located in the Trans-Mexican Neovolcanic Belt. A complex hydrogeological system was approached, composed of metamorphic rocks, covered by sedimentary rocks of marine origin and folded, covered by tertiary clastic rocks and a volcanic sequence of Quaternary age. The main objective of this research was to carry out a hydrogeochemical characterization to identify hydrogeochemical processes. The interaction with different geological units and anthropogenic activities produces different water types (facie Ca–Mg–Na–HCO3–SO4 in the urban area, Ca–Na–Mg–HCO3 agricultural area). It was determined that the local flow contributes 55%, the intermediate 26%, and the regional 19% with ternary mixtures model. With speciation diagrams, the conditions of chemical equilibrium in the aquifer are determined. Given this scenario, inverse modeling was applied in a cross-section to identify water interaction with the different types of geological materials through which it circulates and anthropogenic activities. The inverse modeling in cross-section 71-61, from the Pico de Orizaba recharge zone, indicates that the main processes present are altering silicates and clays (albite, illite, Ca-montmorillonite, gibbsite; dolomite, halite and gypsum dissolution; calcite and kaolinite formation). In cross-section 61-51, the model shows albite, gibbsite, Ca-montmorillonite alteration; dolomite and halite dissolution; also, calcite, gypsum, kaolinite, and illite formation. In cross-section 51-53, the modeling indicates albite, gibbsite, illite, Ca-montmorillonite alteration; halite and dolomite dissolution; also, gypsum, calcite, kaolinite, formation; NH3 (g), NH4, N (2) (g), ion exchange of NaX. The organic matter plays an essential role in REDOX conditions due to anthropogenic activities of the study area.