Hydrogeochemistry and water-rock interactions in the urban area of Puebla Valley aquifer (Mexico)

The urban area of Puebla Valley aquifer is seated in Puebla City and neighbor municipalities. Puebla is the fourth largest city in Mexico, where there are significant industrial zones and a large population. Water needs are almost exclusively met by groundwater, which has brought intense exploitation of groundwater resources and water quality degradation. The present study investigates the hydrogeochemical changes in groundwater, particularly focuses on the chemical changes produced by upwelling mineralized water. These concentrations may represent potential risks to the health of the population. The groundwater presented five types of families Ca-HCO3, Mg-HCO3, Mix-HCO3, HCO3-Ca-SO4 and Ca-SO4. The high concentrations of sulphates, calcium and magnesium are reflected in high TDS and Total Hardness. The samples collected showed detectable concentrations of F, Fe, Mn, Ba, Sr, Cu, Zn, B and Li. The limitations for its use as drinking water are given by the high values of TDS, sulphates, total hardness and Mn. Geochemical modeling using Geochemist's Workbench (GWB) and PHREEQC software enabled the computation of the saturation index of mineral phases with ions in solution and speciation ions. Groundwater was initially in equilibrium with calcite; however, due to the changes in hydrogeological conditions, gypsum and dolomite are being dissolved until new equilibrium conditions are met. The additional calcium and carbonate in the water causes calcite to become oversaturated and to precipitate. Evidence of dedolomitization reactions and common ion effect is illustrated by concurrent increases in calcium and magnesium concentrations in the groundwater.