Vulnerability assessment of an aquifer in an arid environment and comparison of the applied methods: case of the mio-plio-quaternary aquifer

Protecting the quality of water resources has become a priority in Algeria and in several countries around the world, due to droughts and proliferation of pollution sources, such as domestic and industrial wastewater discharges, raw discharges, chemical fertilizers, etc. The valley of Oued Righ, which is one of the oldest cultivated areas and one of the best known of the Algerian northern Sahara, has experienced significant population growth and appreciable agricultural development. The water needs in this region are provided from groundwater resources, contained in the aquifers of the Terminal Complex and Intercalary Continental, and topped by the Quaternary aquifer. The present study focuses on the aquifer in the Mio-Plio-Quaternary of Oued Righ Valley, in order to assess and map its vulnerability to pollution, by applying the DRASTIC and GOD methods. The comparative study, based on Kendall test, showed that the two methods present moderate agreement (W = 0.703). The statistical analysis of different vulnerability classes revealed that vulnerability assessment, using the DRASTIC method, may be represented by four classes: "Very low", "Low", "Medium" and "High", with a dominance of class "Medium" (74.30%). The GOD method resulted in vulnerability that sits between two classes, 'Low' and 'Medium', with a noted domination of class "Low" (70%).Comparison of the two vulnerability maps obtained from the DRASTIC and GOD methods shows that the DRASTIC method better represents the distribution of degrees of vulnerability to pollution in the aquifer of the Mio-Plio- Quaternary.