Anthropic effects on hydrochemical characteristics of the Valle de Toluca aquifer (central Mexico)

The Valle de Toluca aquifer, located in the Highlands of Mexico, is subject to intensive exploitation to meet the water demand in the valley, as well as for part of Mexico City. This intensive exploitation has produced a decline in groundwater level, land subsidence problems and a decrease in river and spring flows. This study is aimed at determining the extent to which the intensive groundwater abstraction is able to affect and modify the chemical characteristics of the water, using statistical techniques and historical data on the main physico-chemical parameters. Some changes in the chemical characteristics have been verified; initial water abstractions were mainly derived from a local flow zone (rainwater recharge and lateral flows from other aquifers), but currently the chemical characteristics are those of a regional flow zone, revealed by waters of sodium bicarbonate type. An increase in nitrate content has also occurred, although only occasionally is the limit for potable water (50 mg NO3- L-1) exceeded.