The combination of the modified DRASTIC and GOD methods for assessing the vulnerability to pollution of the Middle Cheliff aquifer, Algeria

The Middle Cheliff basin (Algeria) is located in an area where groundwater is limited and undergoes excessive withdrawal for water supply, irrigation and industrial purposes. These uses, combined with the scarcity of rainfall, lead to the contamination of the water resources. This study aims to assess the vulnerability to pollution of the Middle Cheliff aquifer by the application of GOD and the modified DRASTIC methods. The use of these methods resulted in the development of two vulnerability maps, which were tested and validated using the distribution of nitrate in the aquifer during May 2012. A comparative study of the two methods based on Kendall’s test and the statistical analysis of the different classes of vulnerability revealed that the vulnerability by the modified DRASTIC method is represented by four classes: low, medium, high and very high, with the predominance of the medium class (58.3%). The GOD method also resulted in four classes of vulnerability (low, medium, high and very high), and the medium class is again predominating (74.1%). The analysis of surfaces by classes of both methods revealed that 78.76% of the mapped area has identical indices. The vulnerability maps constitute a tool for water resources management in the Middle Cheliff basin.