Geophysical and Hydrochemical Study for the Implantation of Ten Boreholes in the Schisto-Limestone Group: Nkayi-Loudima Zone (Bouenza Department)

Abstract

In the aim of supporting the implementation of basic community infrastructure (drinking water, schools, hospitals), ten hydraulic boreholes with human-powered pumps (HPP) were built in the districts of Kayes and Loudima in the Bouenza department in the southwest of the Republic of Congo. However, there is no study that has assessed the quality of groundwater in this area. The electrical train profiles carried out in the study area revealed several anomalies which are mainly of type (V). The interpretation of the anomalies along the electrical drilling profiles yield to characterize the variation of the thicknesses of the potential aquiferous horizons in units of the Schisto-calcaire Group. Therefore, eight positive drillings having been implemented in the carbonates layers of the Schisto Calcaire Group. The physico-chemical analyses of the groundwater showed that the waters are weakly to moderately mineralize with electrical conductivity values lower than 1000 µS/cm. These waters are divided into two chemical families of waters: chloride sulfate calcic and magnesian and bicarbonate calcic and magnesian. Also, pH and saturation values obtained indicate that the groundwater of the area is aggressive. The major elements of the groundwater in the Madingou-Nkayi-Loudima area have levels below the maximum allowable concentrations defined for drinking water by the WHO. Furthermore, all the sampled water hadvery high levels of heavy metals such as cadmium, and their levels of minor elements (iron, fluorine, copper, aluminum and manganese) at some water points exceed the maximum allowable concentrations defined for drinking water by the World Health Organization. In addition, the study of water suitability for irrigation using the USSL Richards diagram, showed that the groundwater has good quality (class C1-S1) and can be used for irrigation for all types of plants and soils.