Abstract
The phreatic aquifer of Oued Guéniche (prefecture of Bizerta, northeast of Tunisia) which occupies an area of 83 km2 has a great economical importance because it is used for irrigation and domestic consumption. The area of the aquifer is essentially occupied by agricultural zones, characterised by an increasing use of chemical fertilizers. Those chemical fertilizers threaten the quality of the ground waters. The study of the vulnerability to pollution of this aquifer was made by applying two vulnerability methods: the generic DRASTIC which is an intrinsic vulnerability method, and the Susceptibility Index (SI) which is a specific vulnerability to agricultural pollution method. This study employed the Geographical Information System (GIS) technology as a system for the acquisition, storage, analysis and display of geographic data. The validity of the two methods to agricultural pollution by nitrates was verified by comparing the distribution of nitrates in the groundwater with the distribution of the different vulnerability classes. That comparison demonstrated that the SI method is the more valid method in the studied system.