HYDROGEOCHEMICAL BEHAVIOR OF A COASTAL AQUIFER FROM SEMI-ARID AREAS: CASE OF BARREMIAN-APTIAN AQUIFER OF ESSAOUIRA BASIN (WESTERN MOROCCO)

This study enters in the identification of factors influencing the waters mineralization of the Barremian-Aptian aquifer of the Essaouira Basin (southwest Morocco). To perform this investigation, 26 water samples were collected and analyzed in June 2015. The results of chemical analysis were treated with hydrochemical and statistical methods (Principal Component Analysis (PCA) and Agglomerative hierarchical clustering (AHC)). A geographic information system (GIS) was established to study the spatial variation of salinity and trace the piezometric map of the studied aquifer. The hydrochemical approach showed that the water is slightly mineralized and have three types of chemical facies: (1) Ca-Mg-Cl (54%), (2) Ca-Mg-HCO 3 (31%) and (3) Na -K-Cl (11%). This technique has demonstrated that mineralization of the waters of the Barremian-Aptian aquifer of Essaouira Basin is the result of two phenomena: (i) the dissolution of the rock by water-rock contact, (ii)  ion exchange  processes  and (iii) contributions waters by superficial infiltration. These two phenomena are confirmed by the ACP statistical techniques. The AHC has shown the existence of three groups of water with different chemical compositions.