Quality of urban runoff in wet and dry seasons: a case study in a semi-arid zone.

Urban runoff (UR) is a promising new resource that may alleviate growing tensions in numerous arid and semi-arid regions of the world. However, it is precisely in these zones that the available UR quality characteristics are scarcer. This work aims to evaluate a wide set of parameters to establish a detailed approach to both the quality of UR in a midsized city in Central Mexico and the feasibility of using UR to recharge aquifers. UR from an institutional land use site was sampled during wet and dry seasons and assessed for suspended solids, organic matter, nutrients, microorganisms, metals, and persistent organic chemicals (i.e., polycyclic aromatic hydrocarbons, PAH). The results were analyzed using multivariate statistical methods to identify relationships among the variables, the sampling sites and the seasons. The soil erosion and the leaching of materials due to the water flow through vegetated areas were identified as the most influencing factor on the quality of the site runoff in both dry and wet seasons. Additionally, data were more heterogeneous during the dry season, and higher pollutant concentrations were found both during the dry season and in more pervious zones. We consider UR a promising water source for recharging aquifers in arid and semi-arid zones if a program is implemented that can integrate an adequate runoff treatment system, soil protection, and other non-structural measures.