Evaluation of groundwater vulnerability to pollution using a GIS-based multi-criteria decision analysis

Abstract

The groundwater contamination is due to different factors such as rapid urbanization, intensive fertilizer application, and wastewater disposal systems associated with human settlements and industries activities. Vulnerability mapping is considered as a fundamental aspect of sustainable groundwater management especially in overexploited and threatens aquifers by various sources of pollution. In the present study vulnerability and risk pollution maps were produced using a GIS based-multi-criteria decision analysis in an appropriate case study in Agareb area (southern Tunisia),and the results were validated using nitrate concentration. Eight appreciation criteria such as: aquifer type, hydraulic conductivity and depth to water table, slope, and proximity to concentrated land use, proximity to rivers, proximity to residential areas and proximity to main roads were selected. These factors were rated in one common interval from 0 to 10 using the fuzzy membership functions. Analytic Hierarchy Process (AHP) is adopted to weight factor assessment. The final groundwater vulnerability maps were created by weighted linear combination (WLC). The results reveal that about 1% area is covered under very high vulnerable zone, 6% area under moderately high vulnerable zone, 18% area under moderately vulnerable zone, 25% area under moderately low vulnerable zone, and 50% area under low vulnerable zone. The results were validated using nitrate concentration in groundwater. Observed nitrate concentrations in boreholes are in accordance with the vulnerability map. The GIS-based multi-criteria decision analysis was observed to be more conclusive in groundwater vulnerability assessment in overexploited areas.