Abstract

This paper presents a hydrogeochemical characterization of the Paleocene aquifer in the coastal basin of Togo. During the dry season (March, 2005), piezometric measurements were made on inventoried water wells. Fifty nine (59) water samples were taken for chemical analysis and the results subjected to statistical study. The quantitative variables considered for this purpose were temperature, pH, electrical conductivity, the major and some minor elements. The results showed that the water samples were weakly mineralized. The electrical conductivity did not exceed 1000 µS/cm, but it increased considerably in the sulphate rich samples. Hydrochemistry was dominated by calcium and bicarbonate except where important values of sulphate (967 mg/L) were obtained. The results of chemical analysis allowed the definition of four different hydrochemical facies. The calcic and magnesian bicarbonated facies was the most important. A sodic and potassic bicarbonated facies identified was mainly due to the residence time of water in the reservoir. Principal component analysis showed one pole of mineralization with strong correlations between sulphate, carbonate, magnesium and calcium.

Key words: Hydrochemistry, aquifer, chemical facies, residence time, Paleocene, Togo.