Open Journal of Modern Hydrology, 2013, 3, 130-137 doi:10.4236/ojmh.2013.33017 Published Online July 2013 (http://www.scirp.org/journal/ojmh) Copyright © 2013 SciRes. OJMH Groundwater Chemical Evolution in the Essaouira Aquifer Basin—NW Morocco Mohammed Bahir 1 , Rachid El Moukhayar 1 , Najiba Chkir 2 , Hamid Chamchati 1 , Paula Galego Fernandes 3 , Paula Carreira 3 1 Geodynamics Laboratory Magmatic Géoressources and Georisks, Université Cadi Ayyad, Marrakech, Morocco; 2 Geography De- partement, Faculty of Letters and Humanities, Sfax University, Sfax, Tunisia; 3 Nuclear Technology Institute, Sacavém, Portugal. Email: bahir@ucam.ac.ma Received September 19 th , 2012; revised October 20 th , 2012; accepted October 28 th , 2012 Copyright © 2013 Mohammed Bahir et al. This is an open access article distributed under the Creative Commons Attribution Li- cense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT The sustainability of groundwater resources for drinking water supplies, agriculture, and industry a prime concern in countries dominated by arid and semi-arid climates such as Morocco. The growing demand for groundwater coupled with impacts from land use and climate change make sustainability an even more important water management goal. In order to make sound decisions about water use and protection of water quality, managers and policy makers must have a sound understanding of such factors as the location and amount of groundwater recharge and groundwater ages. Due to the population growth and climate change (causing long periods of drought) in the world, many countries have inten- sively increased their use of water sources for supplying potable water to population and for their agricultural (irrigation) and industrial developments. Due to the lack of surface waters, people exploit mainly underground water reservoirs. So, it is necessary to study and characterize these water reservoirs to avoid any excess of exploitation. The water resources of the Essaouira basin are characteristic of a semi-arid climate, and are severely impacted by the climate (quantity and quality). Considering the importance of the Essaouira aquifer in the groundwater supply of the region, a study was con- ducted in order to comprehend this aquifer groundwater evolution. It is an aquifer located on the Atlantic coastline, southern (Morocco), corresponding to a sedimentary basin with an area of near 200 km 2 . Covering the Palaeozoic bed- rock, the sedimentary series range from the Triassic to the Quaternary. The geological structures delineate a syncline bordered by the Tidzi diapir of Triassic age which outcrops to the East and South. In the Essaouira basin a multi-aquifer was identified constituted by detrital deposits of the Plioquaternary and dolomitic limestones of the Turonian. The Plioquaternary is unconfined below the Senonian marls. However, in some places it can be in direct contact with the other Cretaceous and Triassic units. The Plioquaternary is generally up to 60 m thick. The Turonian is confined by the Senonian marls and in direct contact with the Plioquaternary on the edges of the syncline structure. The main flow di- rection is from SE to NW towards the Atlantic Ocean, being the recharge area located near the Tidzi diapir. In the Es- souaira basin, in spite of the occurrence of calcareous and dolomitic levels, all waters are of Na-Cl-type. The chemical signature of these waters should be the result of the preferential recharge area that is located in the Tidzi diapir. Using a simple mass balance model through the PHREEQC program this scenario was tested. The reaction path was assumed to be such that waters observed at shallow depths evolved to more mineralized waters. It was possible to notice that these waters have an important contribution of water-rock interaction in groundwater mineralization, corroborating the influ- ence of the preferential recharge area located in the Tidzi diaper in the waters signature. Keywords: Essaouira Basin Aquifer; Hydrogeochemistry; Mass Balance Model 1. Introduction Morocco is characterized by a semi-arid to arid climate, excluding a humid zone in the north. This climat con- straint requires the application of new technologie to supplement conventional hydrological method, in order to improve water resources assessment and management in Morocco. In coastal regions, the problems related with the in- crease of salinization and pollution in groundwater sys- tems is generally associated to the effects of seawater (seawater intrusion by overexploitation of the system and by sea-salt-spray) and on the other hand by the anthro- pogenic activities such as domestic wastes, agriculture