Hydrochemical features and mineralization processes in coastal groundwater of Oualidia, Morocco

• Samples were taken from 19 wells during June, December 2010, and May 2011 periods.
• This study aims to investigate origin and process of groundwater mineralization.
• Distance from coast and morphological aspect emphasized mineralization.
• Groundwater salinity was due to seawater intrusion in areas at 1 km from ocean.
• Cation exchange, evaporation and evaporate dissolution induce groundwater salinity.

The objective of this study is to identify the influence of different hydrochemical processes, potential salinity sources, and seawater intrusion on groundwater quality in the coastal region of Oualidia. For this purpose, chemical analyses were performed on 19 wells sampled during three campaigns: June and December, 2010 and May, 2011. Investigations were conducted to identify the significant chemical variations between different campaigns. In addition, chemical variations were controlled by two main factors, which are the distance from the coast and the morphological aspect. Furthermore, statistical analysis allows the identification of two clusters of samples. The first groups, near the ocean, are highly mineralized with dominance of Na+ and Cl− ions, while the second group, much farther from the coast, are slightly mineralized with dominance of Ca2+ and HCO3− ions. Besides, ionic ratio, ionic delta, saturation index, and Gibbs diagram were applied to evaluate geochemical processes responsible for groundwater mineralization. Results showed that salinity was due mainly to seawater intrusion, especially in the first kilometers from the ocean covering the first group of wells. Moreover, cation exchange between Na+, Ca2+, Mg2+, and K+, evaporation, and evaporate dissolution are principal processes, which also contribute to groundwater salinization. In overall, this investigation provided a basis of geochemical data to effectively manage groundwater resource and efficiently mitigate impacts on aquifers.