Groundwater Pollution Risk Mapping Using Index Methods (North-East Tunisia)

The aim of this study is to assess, within a GIS, the pollution risk of the Mornag groundwater using the DRASTI-LU and SI index methods, and to validate the resulting maps with geochemical data. To achieve this objective, four risk maps were created by combining hydrogeological and geochemical data. 41 samples were analyzed to validate the risk maps developed. Each risk map was calcified using four reclassification methods so that a total of 16 risk maps were produced. The spatial distribution of groundwater contamination risk allowed results to be compared by classifying them into five risk classes: very low, low, medium, high, and very high. All the resulting risk maps show that the downstream part of the aquifer is the riskiest to pollution compared to the other areas. In fact, the results of validation of the risk maps show that relatively the best map with the lowest correlation index is the one made by the DRASTI-LU method obtained by the additive combination with a weight of 5 for the land use parameter. The coincidence between the nitrate concentration distribution and the spatial distribution of risk degree confirms that the study area is affected by anthropogenic pollution more precisely agricultural pollution by nitrates.