Hydrogeochemical Assessment of Groundwater in Central Region of Somalia

Groundwater is an important water resource in Central Somalia. The purpose of this paper is to evaluate the groundwater quality in the area based on geological, hydrogeological, and hydrochemical investigations. The study area covered by varying thickness of red Sand, Gypsum, caliche and limestone overlay limestone, marl, gypsiferous interbedded with clays, and sand of Tertiary age, unconformably overlying the Cretaceous limestone, gypsiferous limestone, gypsum, sand and sandstone deposited under continental, lagunal, and shallow marine environments proceeding from the border with Ethiopia toward the coast. The general groundwater flow direction in the study area is from west south west to east north east toward the coastal plain, but there are some exceptions with local water storage. The aquifer system of the study area consists of two aquifers and the two of them seems to have inherited its physic-chemical properties from the hosting sedimentary formations. Natural minerals dissolution, ion exchanges and evaporation play a prominent role in the ion enrichment of groundwater. The total dissolved solids, electrical conductivity, total hardness, and sodium-adsorption ratio values tend to increase towards the central zone. The groundwater type is Ca2+- Mg2+-Cl--SO42- and Na+-Mg2+-CL- water types and close to coastline groundwater is chloride- sodium type, reflecting the effect of marine intrusion. The results also showed that groundwater quality in the study area in relation to WHO water quality standards is unsuitable for drinking purposes. Extraction from only the lower aquifer with sealing of the upper one is recommended within the saline zone.