Hydrogeochemical Characterization of the Jerez Aquifer, Zacatecas, Mexico

Twenty-nine groundwater samples were collected to define the hydrogeochemistry and quality of groundwater in the Jerez aquifer. These were used to determine major anions and cations as well as trace elements, in the laboratories at the Autonomous University of San Luis Potosi. Along with the use of Piper and Stiff diagrams, three groups of water were identified: sodium bicarbonate, mixed bicarbonate and calcium bicarbonate. The sodium bicarbonate has the longest relative residence time in the aquifer. It circulates through fractured media composed of clastic volcanic rock. It also has the highest F and temperature averages in the system. The presence of a regional flow system is inferred. The temperatures of the mixed bicarbonate water are moderate, it circulates through granular media and likely corresponds to intermediate flow systems. Lastly, the calcium bicarbonate family has lower concentrations of Cl, indicating a local flow system. It circulates through a granular medium and has the shortest relative residence time in the aquifer. In general terms, the water quality is good, given that STD, SO4, N-NO3 and Cl concentrations are within the allowable limits established by NOM-127- SSA1-1994, 2000. Nevertheless, concentrations of As and F ions in some of the wells located in the center and northeast parts of the aquifer exceed official norms, indicating it is not suitable to use as potable water.