Theoretical analysis and considerations of the main parameters used to evaluate intrinsic karst groundwater vulnerability to surface pollution

Karst aquifers are highly susceptible to surface pollution scenarios due to exokarst features allowing a fast infiltration regime, bypassing the unsaturated zone. Intrinsic vulnerability maps are a visual interpretation of different levels of vulnerability estimated from multiple arrays of natural characteristics of the aquifer. However, for karst aquifers, this type of analysis is affected by the high subjectivity and personal interpretations of some karst features from hydrological or geological points of view. Current methodologies to assess groundwater vulnerability in karst differ in the number and type of evaluated parameters; they have unsimilar rates, weights, and sometimes a contradictory evaluation of some karst features' hydrogeological behaviour. This paper reviews the main parameters utilized to obtain intrinsic vulnerability maps, including their rating and weighting process, in order to provide additional insights and assist on the process of groundwater vulnerability analysis. After the review of twelve methodologies' guidelines and their application on 45 study areas around the world, new considerations to evaluate parameters and the assignation of rates and weights, according to infiltration scenarios, are here proposed.