Groundwater recharge and pollutant transport beneath wastewater irrigation : the case of Leon, Mexico

Agricultural irrigation with wastewater is widely established in Mexico. The city of Leon is the centre of the Mexican tanning industry, and produces wastewater with a significant component of industrial effluent. The city is one of the fastest growing in Mexico and is highly dependent on groundwater for public supply. Much of this is drawn from aquifers around the city, including those beneath the wastewater area. The sources of recharge to these aquifers and the types of pollution are reviewed. Regionally, groundwater levels are falling as a result of excessive groundwater abstraction, but within the area of wastewater irrigation groundwater levels are maintained close to the surface. Groundwater sampling from existing boreholes, surface geophysics, soil sampling and the drilling of cored investigation boreholes have been able to identify a body of shallow polluted groundwater within the wastewater area and contrast this with the regional groundwater quality. The most immediate threat to public water supply from pollutants originating in the wastewater is posed by salinity. The predicted consequences of various management options for reducing the impact of wastewater on the quality of deeper groundwater are briefly discussed