The EU Cooperation in Science and Technology (COST) Action 620 Group approach is applied to evaluate the risk of groundwater contamination of a karstic aquifer located southeast of Mexico, to get information of potentially threatened areas. Subsurface contaminant loads, the aquifer vulnerability, as well as, the interaction between them are considered to define the aquifer risk to contamination. The hazard and risk indexes are calculated from an inventory of contaminant sources, creating their maps using geographic information system. Under the COST 620 approach, any method can be used to analyze aquifer vulnerability to contamination and new ones can be developed. This allows to model the karst groundwater vulnerability to contamination in the study area, applying a modified version of the DRASTIC method, where considerations are given to hydraulic conductivity and land use, as parameters in the model. The results indicate a more conservative differentiation when compared to similar studies carried out in the study area with the moderate vulnerability class occupying the greatest extent. Areas of high hazard and risk are in the main urban areas.