Hydrochemical Approach to Groundwater in the Environment of the Public Discharge of Lake Mbeubeuss (Dakar, Senegal)

Abstract

To determine the origin and the processes of groundwater mineralization in the Mbeubeuss lake area, the major ion concentrations of the groundwater were compared to those of the rainwaters which constitute the input function of the aquifer of the Quaternary sands in the area of lake Mbeubeuss. The physico-chemistry of groundwater near the public discharge and its surroundings, has shown that the true value of the electrical conductivity of waters are around 2000 µS/cm. Values of electrical conductivity greater than 2000 µS/cm would represent the particular mineralization of ground waters by the public discharge of lake Mbeubeuss. The chemical facies of ground waters are dominated by the sodium and potassium chloride and calcium chloride facies. The study of the relationship between the major chemical elements and the chloride ion and the representation in the modified Chadha diagram of the chemical analyzes of ground waters from the campaigns of July 1998, July 2002 and March 2003, made it possible to highlight the different sources and processes controlling the mineralization of ground waters in the Mbeubeuss Lake area. Despite the proximity to the sea which suggests a considerable contribution of salts by aerosols and sea spray, the mineralization of ground waters in the area of lake Mbeubeuss is largely due to leachate from household waste and the influence of old sediments of the dry lake Mbeubeuss. The main processes controlling the mineralization of ground waters are marine contributions (aerosols and sea spray), dissolution-precipitation of minerals from the aquifer matrix, atmospheric CO2 diffusion, base exchanges, dilution-concentration and anthropogenic pollution.