HYDROCHEMISTRYOF GROUNDWATER IN KHARTOUM STATE CENTRAL SUDAN

Abstract

Abstract The groundwater chemistry of Khartoum State between longitudes 32° 00'-33° 0O’E and latitudes 15° O0’-16° 00'N was evaluated and assessed using different hydrogeological methods. Groxmdwater in the region occurs in two hydraulically interconnected aquifers. The siliciclastic sediments of the Cretaceous Omdurman Formation form the lower one, and the mostly unconsolidated sediments of the Cretaceous-Tertiary- Quaternary Umm Ruwaba Formation comprise the upper one. The evaluated hydrodynamic properties revealed unconfined conditions in most parts of the aquifers system and partial confinement in some parts, where clayey zones occur. The analysis of flow system indicated a regional flow direction towards the northwest, with a local flow regime towards the east. Preliminary assessment of grormdwater chemistry was investigated by using different statistical technique such as X-Y plots, correlation, cluster, principle components, and factor analyses. The results of analyzing data by these techniques showed negative correlation between the exchangeable ions, Na-Ca and Na-Mg, which means ion exchange process is active. The strong correlations among Na’ and Cl‘ ions, TDS and EC indicate that salinization is related to the increase of concentration of these ions. Dissolution process of evaporitic mineral is suggested by the strong positive correlations between Ca”, Mg” and SO42" Groundwaters were classified by

-grouping them‘ into faeies~ For ~the—purpose of -classification, the pattern diagram of Lee, trilinear plots of Hill-Piper, Durov and by Chadha diagram. Three main types of hydrochemical facies were recognized, Ca-Mg-HCO,, Ca-SO,-HCO, and Na-Ca-S04-Cl. The spatial distribution of these facies and hydrochemical sections, indicate that the anionic facies changes in the flow direction from HCO,’ to SO42’ and finely to Cll. The cationic facies is mostly affected by ion-exchange process of calcium and magnesium by sodium. Mixing is an important and active process that has affected the water facies in the region. The saturation state of groundwater showed that, it is saturated with respect to carbonate minerals and undersaturated with respect to CO2 and sulphate. Assessment of groundwater quality at different locations indicated its suitability for all purposes except at few specified localities.