The chemical composition of groundwater is a product of the evolution and transformation of major ions, which come from natural hydrogeochemical processes or from anthropogenic interference. The objective of this study was to identify the hydrogeochemical processes and the influence of anthropogenic activity on the variation of chemical composition in Toluca Valley groundwater. The type of water in the zone is fundamentally Mg-Ca-HCO3. Three groups with different evolutionary tendencies were identified: one within a local recharge zone and two others in an intermediate region with anthropic activity. The latter, which show contamination by inorganic matter (fertilizers) and organic matter (urban or industrial wastewater). The content of N-NO3- (0.024-0.219 mEq L-1), N-NH4+ (0-0.022 mEq L-1), Porg (0.03-1.02 mEq L-1) and PO43- (0.0-0.28 mEq L-1) indicated contamination coming from inorganic and organic matter. These chemical compounds were identified by way of a 3D fluorescence technique. The results of this study demonstrate that the main processes that affect and control the chemical composition of the water in the Toluca Valley aquifer are weathering of silicates, the ion exchange and a mixture process generated by a source of anthropic contamination.
Keywords: Anthropogenic pollution; Dissolved organic matter; Ion exchange processes; Mixing water.