Assessment of groundwater quality from semi-arid area for drinking purpose using statistical, water quality index (WQI) and GIS technique

This study aims to assess the groundwater status of a basin in a semi-arid climate, based on the hydrogeochemical, piezometric, statistical and geographic information system (GIS) approach. The region held as an example is the upstream part of the Essaouira basin (Morocco). Analysis of the evolution of the rainfall series by applying the Pettitt and Mann–Kendall tests shows a rainfall deficit of around 14% for the study period (1940–2015). For temperatures and with the application of both tests, an upward trend was observed with a warming of about 2.3 °C for the period 1987–2014. The same trend was observed for ETP, with an increase of around 5 mm for the period 1987–2014. The piezometric study shows a general decrease in the piezometric level over the last 24 years, as a result of the rainfall deficit. The hydrogeochemical approach shows (1) the dominance of the mixed Ca–Mg–Cl and Ca–Cl facies and that by passing from one campaign to another, groundwater generally keeps the same facies; (2) groundwater mineralization is controlled by the phenomenon of dissolution of evaporite and carbonate minerals and by the phenomenon of reverse ion exchange; (3) water quality index (WQI) values show that groundwater quality is becoming increasingly poor from each year to the next. However, the results obtained could be a reference to decision makers to protect this vital resource.