Spatial distribution of δ18Oin rainwater and groundwater to identify areas of recharge in the Colombian Northwest

The understanding of the spatiotemporal variability of the water moleculestable isotopes(delta 18Oand delta 2H)in rain and groundwater has been used in hydrogeologyto validate recharge zones. In this study, we analyzed the recharge of four aquifersystems located in northwestern Colombia. This region is characterized by highlycomplex topography, as the Andes Mountain range splits into three branches, two ofthem included in the study area. The relation in the variation of values of the delta 18Obetween Precipitation (P) and groundwater (GW) was analyzed through the arithmeticexpression P/GW; when P/GW is equal or larger than 1, the recharge is direct, andvalues less than 1 indicate recharge from regional flows. For the purposes of thisresearch, according to statistics criteria, values between 0.98 and 1.02 are consideredas 1. It was found that on Bajo Cauca, Occidente and Urab & aacute;, the phreatic aquifersare recharged directly with rainwater or after slight evaporation processes, while therecharge of deep aquifers occurs through regional flows. The Valle de Aburr & aacute; s phreaticaquifer is also recharged from distant areas; this occurs because the surface has beenimpermeabilized by urban processes. The P/GW ratio seems to be useful in identifyingrecharge processes in regions with higher elevation gradients. In low-lying areas, theapplicability of this method should be restricted.