Evaluation of the groundwater quality in the Ghallil quaternary basin (Todgha downstream, South - Eastern Morocco)

Résumé

The Ghallil basin is located in the Todgha lower valley (South-Eastern Morocco). The quaternary unconfined aquifer is dominated by wady alluvium, water samples (5 water points in total) were taken; the analyzed chemical elements are Chlorides, Nitrates, Sulfates, Sodium, Potassium, Calcium and Magnesium. The aim of this study is to assess the groundwater quality of the Ghallil, and to provide information on the origin of their provenance, and their behavior through geological formations.

The results also made it possible to determine the physico-chemical characteristics of groundwater in the Ghallil basin. The groundwater temperature varies between 15.1 and 49°C. The pH is close to neutral; and varies from 6 to 8. The electrical conductivity (EC) of the water points vary between 500 and 1600µm/cm, these EC values result from the leaching out of the reservoir rock in which the water was staying.

The analysis of the groundwater quality revealed that 40% of the points checked are of good quality, 20% are of average quality, and 40% are of poor quality. The chemical analysis showed that the groundwater of the basin belong to two chemical facies a chlorinated and sulphated calcium and magnesium facies and a sodium and potassium chloride facies.

The deterioration of the groundwater quality in the Ghallil basin could have geological and anthropic origins. The relationship between conductivity and sodium absorption indicates that there is no risk of alkalization while the risk of salinization remains.