Application of the parametric methods (DRASTIC and SI) for the study of the vulnerability in the potential pollution by nitrates of the superficial groundwater of Timahdite-Almis Guigou (Middle Atlas, Morocco)
The fluvio-lacustrine and volcanic Plio-Quaternary hydrogeological aquifer system is located in a recently collapsed subsidence zone between Timahdite and Almis Guigou in the Moroccan Middle Atlas. The study area is essentially occupied by agricultural areas, characterized by a high use of chemical fertilizers and pesticides which represents, in addition to domestic sewage, a permanent risk to groundwater quality. We have studied the vulnerability to pollution of the regional superficial groundwater using two methods, DRASTIC and SI, with the software ArcGIS 9.3 and Erdas Imagine 8.4. The validity of these two methods was tested by comparing the distribution of nitrates in groundwater and the different classes of vulnerability. Three classes of pollution vulnerability degrees were identified by the two methods (low, average and high). The middle degree of vulnerability class is most dominant with 60% for the DRASTIC method and 49.81% for SI method. The coincidence rate of the groundwater nitrate concentrations with the different vulnerability classes established is 76.92% and 61.54%, respectively for the SI and DRASTIC methods. From this coincidence rate, the SI method seems better for assessing the vulnerability to nitrate pollution.