Hydrogeochemical processes, and health risk assessment of groundwater, in Santa María del rio aquifer: A case study of San Luis Potosí valley, Mexico

The main objectives of this research were to the hydrogeochemical processes that control the groundwater chemistry, groundwater quality, and assessment of health risks of water. The drinking water that supplies the community of Santa María del Rio, S.L.P., comes from groundwater, in some municipality localities, groundwater Fluorine and arsenic are reported. Twenty-one representative groundwater samples were taken. Physicochemical parameters in situ: pH, OD, ORP, Alkalinity, STD, EC, Salinity, Total Coliforms, and E-coli, were analyzed, and in the laboratory, the heavy metals, metalloids and major constituents, cations: calcium, sodium, magnesium, and potassium, were determined by the ICP, and anions: chlorides, and sulfates, by colorimetry techniques. The results of the analyses were compared with the Mexican and EPA drinking water standards to verify their suitability and ensure that they do not exceed the permitted limit values. The results of the chemistry of the principal groundwater ions in the study area suggest that the main hydrogeochemical process that controls the variation of groundwater quality is the rock–water interaction. Groundwater has been classified into two hydrochemical facies, CaMgHCO₃ and NaHCO₃, consistent with the type of rock. The samples with the CaMg–HCO₃ facie are associated with less evolved waters located in areas with local recharge. The dominant reactions in the aquifer are calcite, dolomite, and gypsum solutions. The presence of the N–NO₃^- ion is associated with agricultural and urban zone influence, which indicates that this activity has impacted the water quality. The risk index (HI) results show that values > 0.1 < 1 of HI, for Pb present low chronic risks for adults and children. In contrast, HI values > 4 for both population groups represent high chronic risk. Excessive use of fertilizers should be controlled in the study area to prevent groundwater contamination by heavy metals and metalloids and be measured regularly to check drinking water quality.