Groundwater hydrochemistry of an overexploited aquifer: the case of the Toluca Valley, Mexico

Abstract

The demographic, industrial and agricultural growth of recent decades in the State of Mexico has caused a considerable increase in groundwater extraction and the overexploitation is mainly due to drinking water, because it is the supply source for the two densely populated zones in the country: the metropolitan areas of Toluca City and Mexico City and its conurbation. In this work, 49 groundwater sources of drinking water were analyzed in two sampling periods (dry and rainy seasons). According to the Electric Conductivity data, 67% of the samples in the dry and 63% in the rainy season presented weak mineralization and the rest of the samples showed medium mineralization. In addition, the values of hardness showed that the water had good quality, with the exception of 3% of the wells in the rainy season, which had medium quality. The corrosion coefficient showed that two samples in the dry season and four in the rainy season had aggressive characteristics that might damage the extraction and distribution networks. The concentrations of major ions (measured by ionic chromatography) in both sampling periods showed this relative abundance: Na + >Mg 2+ >Ca 2+ >K + =HCO 3 ->>Cl ->SO 4 2-. It was found that the HCO 3 -concentration increased with the groundwater flow in the area. Moreover, it was also possible to establish the principal species in solution and to corroborate the hydrochemical change in the area of study. Although there continues to be clear predominance of the Mg-Na-HCO 3 type, the Na-HCO 3 facies showed a progressive increase.

Presence and Distribution of Fluoride Ions in Groundwater for Human in a Semiconfined Volcanic Aquifer

“…According to this behavior and the data obtained from samplings ( Tables 3 and 4) that the water in the aquifers of the Lerma-Chapala basin is of the Ca-HCO3 type (Figures 4 and 5) [24,28,36]; however, for water from wells in the Valley of México basin, 75% could be of the Na-HCO3 type and 25% of the Ca-HCO3 type. Thus, it is possible to say that the hardness in the water of the Lerma-Chapala basin is a mostly due to calcium and in the Valley of México basin only 25% of the wells have calcium hardness.…”