The effects of wastewater irrigation on groundwater quality in Mexico

The main aim of this research was to determine the environmental effects of wastewater irrigation on the subsurface at two locations in Mexico; Leon a nd the Mezquital Valley. Freshly-drilled subsurface sediment samples (both sites) and groundwater samples (Mezquital Valley) were taken at various dep ths. These were analysed for a range of physico-chemical and microbiologica l parameters using standard methods. Elevated concentrations of faecal and total coliforms were recorded at both sites indicating that faecal bacteria had been transported through the subsurface. The level of subsurface conta mination was affected by both spatial and temporal factors with higher coli form concentrations occurring at shallower depths (<10 m below the surface) and at the top of the water table, and during the wet season. Elevated nit rate concentrations were found in all of the Mezquital Valley groundwaters. Thus, wastewater irrigation appears to have had a negative impact on groun dwater quality. In order to mitigate this, treatment of wastewater prior to irrigation and careful irrigation management is recommended. The potential effects of groundwater degradation on public health and the need for guide lines to protect groundwater quality, are discussed. (C) 1999 IAWQ Publishe d by Elsevier Science Ltd. All rights reserved.