Balance hídrico y calidad del agua subterránea en el acuífero del Valle del Mezquital, México central
Keywords: Mezquital, aquifer, balance, groundwater, contamination, geochemistry
AbstractA significant aspect of the Mezquital valley is that it receives approximately 50 m3/s of untreated wastewater from Mexico City. The sewage flows through drains such as the Gran Canal del Desagüe, Interceptor Poniente and the Emisor Central. This untreated wastewater is used for irrigation of approximately 45214 ha, and a portion infiltrates to the aquifer. 81% of the main channels and 52% of the lateral channels are unlined and therefore wastewater recharges directly the aquifer. Two previously undifferentiated aquifers were now detected by means of a hydrogeologic study in the Mezquital valley. Both, a shallow and a deep aquifers, may be interconnected in some points, and in others they may be isolated. As a result from the groundwater balance, it was determined that the main recharge to the Mezquital valley aquifer is the infiltration of untreated wastewater from Mexico City through channels and irrigation returns. Aquifer discharge occurs through springs that discharge into the Tula river. Another portion of the discharge is withdrawn by wells, and the remainder discharges to the north and northeast as surface water drained by the río Salado, and as groundwater flow. During 2007 the static water level reached depths between 10 and 40 m with groundwater flow from south to north. A groundwater balance was performed obtaining 10.6 Mm3/yr as groundwater recharge, 165 Mm3/yr as vertical infiltration to the aquifer, 97.7 Mm3/yr withdrawn by pumping, 71.7 Mm3/yr as groundwater discharge, zero for change in storage and 6.1 Mm3/yr as evapotranspiration. In terms of water quality, most of the 65 chemically analyzed wells were found with sodium and total dissolved solids concentrations above the maximum permissible limit in water for human consumption. In some wells, arsenic, fluoride, and lead have concentrations that exceed the permissible limit. In thirty out of 75 bacteriologically analyzed drinking water wells, total coliforms were detected and several had fecal coliforms.