Validity of Drastic and SI Vulnerability Methods

Abstract

The phreatic aquifer of Oued Gueniche (prefecture of Bizerta, northeastof Tunisia) Which Occupies all area of 83 km(2) has a great economicalimportance because it is used for irrigation and domestic consumption.The area of the aquifer is essentially occupied by agricultural zones,characterised by all increasing use of chemical fertilizers. Thosechemical fertilizers threaten the quality of the ground waters. Thestudy of the Vulnerability to pollution of this aquifer was made byapplying two vulnerability methods: the generic DRASTIC which is anintrinsic Vulnerability method, and the Susceptibility Index (SI) whichis a specific Vulnerability to agricultural pollution method. This studyemployed the Geographical Information System (GIS) technology as asystem for the acquisition, storage, analysis and display of geographicdata. The validity of the two methods to agricultural pollution bynitrates was verified by comparing the distribution of nitrates in thegroundwater with the distribution of the different vulnerabilityclasses. That comparison demonstrated that the SI method is the morevalid method in the Studied system.