Water quality indices for groundwater impacted by geogenic background and anthropogenic pollution: case study in Hidalgo, Mexico

The studies about the quality of groundwater resources are scarce in Mexico, and often they do not consider indicators of geogenic background and anthropogenic pollution. So, we examined the quality of groundwater from five wells of the Apan aquifer (Hidalgo, Mexico). Four of these wells were taken as reference samples, while the Santa Cruz well was considered as the study site because it is locally recognized as a problem due to the geogenic presence of manganese. In all the sites, variables related to mineralization processes were analyzed, and a quality index (MWQI, from mineralization-based water quality index) was calculated. In the study site samples, we also determined several indicators of geogenic background (arsenic, manganese, and other heavy metals) and anthropogenic pollution (as organic matter, nutrients, and several microbial indicators), from which another quality index (GAWQI, from geogenic background and anthropogenic pollution-based water quality index) was calculated. The MWQI values classified the groundwater from all the sites, even that from the Santa Cruz well, as ?excellent for drinking. When the GAWQI was computed for the Santa Cruz site, this groundwater was found ?unsuitable for drinking? due to its extremely high manganese content. We conclude that the GAWQI could represent a valuable communication tool to inform the population and the authorities about the quality of the groundwater resources.