| dc.description.abstract | Aquifers possess distinct mineralogy, diagenetic history, and geochemical constraints, which control the pore water's hydrochemistry. Whenever aquifers exchange groundwater, the incoming groundwater establishes a new chemical driving force, imposing new reactions related to rock-water interactions. This study developed a simple approach to assess the mass balance of the rock-water interaction of the groundwater exchanged between interconnected aquifers. To illustrate the suitability of this approach, it was applied to the Bauru Aquifer System located in Sao Paulo State in southeastern Brazil. The hydrochemical characterization identified three major stratified hydrochemical facies with typical chemical compositions as well as the authigenic mineralogy assemblages. The first and shallowest facies was composed of a variable groundwater composition along with highly diluted water from a recent recharge. The second facies was composed of unconfined bicarbonate calcium rich water with a mineralogy mainly composed of K-feldspar, Mg-montmorillonite, and calcite. The third facies, which was confined and the deepest, was composed of bicarbonate sodium-rich water and mineralogically dominated by Na-, Mg-, and Ca-montmorillonite, calcite, and analcime. Although the replacement of Na by Ca suggests an extensive cation exchange in the deep-confined portion, sodium-rich silicate dissolution and calcium rich clay precipitation were identified as the operating mechanisms promoting Na enrichment and Ca consumption in the water of the closed system. This finding is supported by the authigenic mineral characterization, delta C-13 of the dissolved inorganic compounds, and numerical analysis. The approach developed for this study, which used numerical simulations to calculate the mass balance, was capable of consistently reproducing the water composition and mineralogy changes. | |
